/src/openssh/channels.c

Source
/* $OpenBSD: channels.c,v 1.472 2026/10/15 05:50:32 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains functions for generic socket connection forwarding.
 * There is also code for initiating connection forwarding for X11 connections,
 * arbitrary tcp/ip connections, and the authentication agent connection.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 * SSH2 support added by Markus Friedl.
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 * Copyright (c) 1999 Dug Song.  All rights reserved.
 * Copyright (c) 1999 Theo de Raadt.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <sys/socket.h>
#include <sys/queue.h>

#include <netinet/in.h>
#include <arpa/inet.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <netdb.h>
#include <poll.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "packet.h"
#include "log.h"
#include "misc.h"
#include "channels.h"
#include "compat.h"
#include "canohost.h"
#include "pathnames.h"
#include "match.h"

/* XXX remove once we're satisfied there's no lurking bugs */
/* #define DEBUG_CHANNEL_POLL 1 */

/* -- agent forwarding */
#define NUM_SOCKS 10

/* -- X11 forwarding */
/* X11 port for display :0 */
#define X11_BASE_PORT 6000
/* Maximum number of fake X11 displays to try. */
#define MAX_DISPLAYS  1000

/* Per-channel callback for pre/post IO actions */
typedef void chan_fn(struct ssh *, Channel *c);

/*
 * Data structure for storing which hosts are permitted for forward requests.
 * The local sides of any remote forwards are stored in this array to prevent
 * a corrupt remote server from accessing arbitrary TCP/IP ports on our local
 * network (which might be behind a firewall).
 */
/* XXX: streamlocal wants a path instead of host:port */
/*      Overload host_to_connect; we could just make this match Forward */
/*  XXX - can we use listen_host instead of listen_path? */
struct permission {
  char *host_to_connect;    /* Connect to 'host'. */
  int port_to_connect;    /* Connect to 'port'. */
  char *listen_host;    /* Remote side should listen address. */
  char *listen_path;    /* Remote side should listen path. */
  int listen_port;    /* Remote side should listen port. */
  Channel *downstream;    /* Downstream mux*/
};

/* Context for non-blocking connects */
struct channel_connect {
  char *host;
  int port;
  struct addrinfo *ai, *aitop;
};

/*
 * Stores the forwarding permission state for a single direction (local or
 * remote).
 */
struct permission_set {
  /*
   * List of all local permitted host/port pairs to allow for the
   * user.
   */
  u_int num_permitted_user;
  struct permission *permitted_user;

  /*
   * List of all permitted host/port pairs to allow for the admin.
   */
  u_int num_permitted_admin;
  struct permission *permitted_admin;

  /*
   * If this is true, all opens/listens are permitted.  This is the
   * case on the server on which we have to trust the client anyway,
   * and the user could do anything after logging in.
   */
  int all_permitted;
};

/* Used to record timeouts per channel type */
struct ssh_channel_timeout {
  char *type_pattern;
  double timeout_secs;
};

/* Master structure for channels state */
struct ssh_channels {
  /*
   * Pointer to an array containing all allocated channels.  The array
   * is dynamically extended as needed.
   */
  Channel **channels;

  /*
   * Size of the channel array.  All slots of the array must always be
   * initialized (at least the type field); unused slots set to NULL
   */
  u_int channels_alloc;

  /*
   * 'channel_pre*' are called just before IO to add any bits
   * relevant to channels in the c->io_want bitmasks.
   *
   * 'channel_post*': perform any appropriate operations for
   * channels which have c->io_ready events pending.
   */
  chan_fn **channel_pre;
  chan_fn **channel_post;

  /* -- tcp forwarding */
  struct permission_set local_perms;
  struct permission_set remote_perms;

  /* -- X11 forwarding */

  /* Saved X11 local (client) display. */
  char *x11_saved_display;

  /* Saved X11 authentication protocol name. */
  char *x11_saved_proto;

  /* Saved X11 authentication data.  This is the real data. */
  char *x11_saved_data;
  u_int x11_saved_data_len;

  /* Deadline after which all X11 connections are refused */
  double x11_refuse_time;

  /*
   * Fake X11 authentication data.  This is what the server will be
   * sending us; we should replace any occurrences of this by the
   * real data.
   */
  u_char *x11_fake_data;
  u_int x11_fake_data_len;

  /* AF_UNSPEC or AF_INET or AF_INET6 */
  int IPv4or6;

  /* Set SO_KEEPALIVE on TCP connections */
  int want_tcp_keepalive;

  /* Channel timeouts by type */
  struct ssh_channel_timeout *timeouts;
  size_t ntimeouts;
  /* Global timeout for all OPEN channels */
  double global_deadline;
  double lastused;
  /* pattern-lists used to classify channels as bulk */
  char *bulk_classifier_tty, *bulk_classifier_notty;
  /* Number of active bulk channels (set by channel_handler) */
  u_int nbulk;
};

/* helper */
static void port_open_helper(struct ssh *ssh, Channel *c, char *rtype);
static const char *channel_rfwd_bind_host(const char *listen_host);

/* non-blocking connect helpers */
static int connect_next(struct ssh *, struct channel_connect *);
static Channel *rdynamic_connect_prepare(struct ssh *, char *, char *);
static int rdynamic_connect_finish(struct ssh *, Channel *);

/* Setup helper */
static void channel_handler_init(struct ssh_channels *sc);

/* -- channel core */

void
channel_init_channels(struct ssh *ssh)
{
  struct ssh_channels *sc;

  if ((sc = calloc(1, sizeof(*sc))) == NULL)
    fatal_f("allocation failed");
  sc->channels_alloc = 10;
  sc->channels = xcalloc(sc->channels_alloc, sizeof(*sc->channels));
  sc->IPv4or6 = AF_UNSPEC;
  sc->bulk_classifier_tty = xstrdup(CHANNEL_BULK_TTY);
  sc->bulk_classifier_notty = xstrdup(CHANNEL_BULK_NOTTY);
  channel_handler_init(sc);

  ssh->chanctxt = sc;
}

Channel *
channel_by_id(struct ssh *ssh, int id)
{
  Channel *c;

  if (id < 0 || (u_int)id >= ssh->chanctxt->channels_alloc) {
    logit_f("%d: bad id", id);
    return NULL;
  }
  c = ssh->chanctxt->channels[id];
  if (c == NULL) {
    logit_f("%d: bad id: channel free", id);
    return NULL;
  }
  return c;
}

Channel *
channel_by_remote_id(struct ssh *ssh, u_int remote_id)
{
  Channel *c;
  u_int i;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c != NULL && c->have_remote_id && c->remote_id == remote_id)
      return c;
  }
  return NULL;
}

/*
 * Returns the channel if it is allowed to receive protocol messages.
 * Private channels, like listening sockets, may not receive messages.
 */
Channel *
channel_lookup(struct ssh *ssh, int id)
{
  Channel *c;

  if ((c = channel_by_id(ssh, id)) == NULL)
    return NULL;

  switch (c->type) {
  case SSH_CHANNEL_X11_OPEN:
  case SSH_CHANNEL_LARVAL:
  case SSH_CHANNEL_CONNECTING:
  case SSH_CHANNEL_DYNAMIC:
  case SSH_CHANNEL_RDYNAMIC_OPEN:
  case SSH_CHANNEL_RDYNAMIC_FINISH:
  case SSH_CHANNEL_OPENING:
  case SSH_CHANNEL_OPEN:
  case SSH_CHANNEL_ABANDONED:
  case SSH_CHANNEL_MUX_PROXY:
    return c;
  }
  logit("Non-public channel %d, type %d.", id, c->type);
  return NULL;
}

static void
free_connect_ctx(struct channel_connect *cctx)
{
  free(cctx->host);
  if (cctx->aitop) {
    if (cctx->aitop->ai_family == AF_UNIX)
      free(cctx->aitop);
    else
      freeaddrinfo(cctx->aitop);
  }
  memset(cctx, 0, sizeof(*cctx));
}

static void
channel_free_connect_ctx(Channel *c)
{
  if (c == NULL || c->connect_ctx == NULL)
    return;
  free_connect_ctx(c->connect_ctx);
  free(c->connect_ctx);
  c->connect_ctx = NULL;
}

/* Enable/disable TCP keepalives for X11 and port-forwarding sockets */
void
channel_set_tcp_keepalives(struct ssh *ssh, int on)
{
  ssh->chanctxt->want_tcp_keepalive = on;
}

/*
 * Add a timeout for open channels whose c->ctype (or c->xctype if it is set)
 * match type_pattern.
 */
void
channel_add_timeout(struct ssh *ssh, const char *type_pattern,
    double timeout_secs)
{
  struct ssh_channels *sc = ssh->chanctxt;

  if (strcmp(type_pattern, "global") == 0) {
    debug2_f("global channel timeout %f seconds", timeout_secs);
    sc->global_deadline = timeout_secs;
    return;
  }
  debug2_f("channel type \"%s\" timeout %f seconds",
      type_pattern, timeout_secs);
  sc->timeouts = xrecallocarray(sc->timeouts, sc->ntimeouts,
      sc->ntimeouts + 1, sizeof(*sc->timeouts));
  sc->timeouts[sc->ntimeouts].type_pattern = xstrdup(type_pattern);
  sc->timeouts[sc->ntimeouts].timeout_secs = timeout_secs;
  sc->ntimeouts++;
}

/* Clears all previously-added channel timeouts */
void
channel_clear_timeouts(struct ssh *ssh)
{
  struct ssh_channels *sc = ssh->chanctxt;
  size_t i;

  debug3_f("clearing");
  for (i = 0; i < sc->ntimeouts; i++)
    free(sc->timeouts[i].type_pattern);
  free(sc->timeouts);
  sc->timeouts = NULL;
  sc->ntimeouts = 0;
}

static double
lookup_timeout(struct ssh *ssh, const char *type)
{
  struct ssh_channels *sc = ssh->chanctxt;
  size_t i;

  for (i = 0; i < sc->ntimeouts; i++) {
    if (match_pattern(type, sc->timeouts[i].type_pattern))
      return sc->timeouts[i].timeout_secs;
  }

  return 0;
}

static void
channel_classify(struct ssh *ssh, Channel *c)
{
  struct ssh_channels *sc = ssh->chanctxt;
  const char *type = c->xctype == NULL ? c->ctype : c->xctype;
  const int has_tty = c->isatty || c->remote_has_tty;
  const char *classifier = has_tty ?
      sc->bulk_classifier_tty : sc->bulk_classifier_notty;

  c->bulk = type != NULL && match_pattern_list(type, classifier, 0) == 1;
  debug3("channel %d: classify type \"%s\" (%s) as %s", c->self,
      type ? type : "(null)", has_tty ? "with TTY" : "no TTY",
      c->bulk ? "bulk" : "interactive");
}

/*
 * Sets "extended type" of a channel; used by session layer to add additional
 * information about channel types (e.g. shell, login, subsystem) that can then
 * be used to select timeouts and DSCP values.
 * Will reset c->inactive_deadline as a side-effect.
 */
void
channel_set_xtype(struct ssh *ssh, int id, const char *xctype)
{
  struct ssh_channels *sc = ssh->chanctxt;
  Channel *c;

  if ((c = channel_by_id(ssh, id)) == NULL)
    fatal_f("missing channel %d", id);
  if (c->xctype != NULL)
    free(c->xctype);
  c->xctype = xstrdup(xctype);
  /* Only override deadline if xctype has a more specific match. */
  double xtype_deadline = lookup_timeout(ssh, c->xctype);
  if (xtype_deadline != 0)
    c->inactive_deadline = xtype_deadline;
  channel_classify(ssh, c);
  /* report effective timeout: per-channel if set, else global */
  debug2_f("labeled channel %d as %s (inactive timeout %f)", id, xctype,
      c->inactive_deadline != 0.0 ?
      c->inactive_deadline : sc->global_deadline);
}

/*
 * update "last used" time on a channel.
 * NB. nothing else should update lastused except to clear it.
 */
static void
channel_set_used_time(struct ssh *ssh, Channel *c)
{
  ssh->chanctxt->lastused = monotime_double();
  if (c != NULL)
    c->lastused = ssh->chanctxt->lastused;
}

/*
 * Get the time at which a channel is due to time out for inactivity.
 * Returns 0 if the channel is not due to time out ever.
 */
static double
channel_get_expiry(struct ssh *ssh, Channel *c)
{
  struct ssh_channels *sc = ssh->chanctxt;
  double expiry = 0, channel_expiry;

  if (sc->lastused != 0 && sc->global_deadline != 0)
    expiry = sc->lastused + sc->global_deadline;
  if (c->lastused != 0 && c->inactive_deadline != 0) {
    channel_expiry = c->lastused + c->inactive_deadline;
    if (expiry == 0 || channel_expiry < expiry)
      expiry = channel_expiry;
  }
  return expiry;
}

/* Returns non-zero if there is an open, non-interactive channel */
int
channel_has_bulk(struct ssh *ssh)
{
  return ssh->chanctxt != NULL && ssh->chanctxt->nbulk != 0;
}

/*
 * Register filedescriptors for a channel, used when allocating a channel or
 * when the channel consumer/producer is ready, e.g. shell exec'd
 */
static void
channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty)
{
  int val;

  if (rfd != -1)
    (void)fcntl(rfd, F_SETFD, FD_CLOEXEC);
  if (wfd != -1 && wfd != rfd)
    (void)fcntl(wfd, F_SETFD, FD_CLOEXEC);
  if (efd != -1 && efd != rfd && efd != wfd)
    (void)fcntl(efd, F_SETFD, FD_CLOEXEC);

  c->rfd = rfd;
  c->wfd = wfd;
  c->sock = (rfd == wfd) ? rfd : -1;
  c->efd = efd;
  c->extended_usage = extusage;

  if ((c->isatty = is_tty) != 0)
    debug2("channel %d: rfd %d isatty", c->self, c->rfd);
#ifdef _AIX
  /* XXX: Later AIX versions can't push as much data to tty */
  c->wfd_isatty = is_tty || isatty(c->wfd);
#endif

  /* enable nonblocking mode */
  c->restore_block = 0;
  if (nonblock == CHANNEL_NONBLOCK_STDIO) {
    /*
     * Special handling for stdio file descriptors: do not set
     * non-blocking mode if they are TTYs. Otherwise prepare to
     * restore their blocking state on exit to avoid interfering
     * with other programs that follow.
     */
    if (rfd != -1 && !isatty(rfd) &&
        (val = fcntl(rfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
      c->restore_flags[0] = val;
      c->restore_block |= CHANNEL_RESTORE_RFD;
      set_nonblock(rfd);
    }
    if (wfd != -1 && !isatty(wfd) &&
        (val = fcntl(wfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
      c->restore_flags[1] = val;
      c->restore_block |= CHANNEL_RESTORE_WFD;
      set_nonblock(wfd);
    }
    if (efd != -1 && !isatty(efd) &&
        (val = fcntl(efd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
      c->restore_flags[2] = val;
      c->restore_block |= CHANNEL_RESTORE_EFD;
      set_nonblock(efd);
    }
  } else if (nonblock) {
    if (rfd != -1)
      set_nonblock(rfd);
    if (wfd != -1)
      set_nonblock(wfd);
    if (efd != -1)
      set_nonblock(efd);
  }
  /* channel might be entering a larval state, so reset global timeout */
  channel_set_used_time(ssh, NULL);
  channel_classify(ssh, c);
}

/*
 * Allocate a new channel object and set its type and socket.
 */
Channel *
channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
    u_int window, u_int maxpack, int extusage, const char *remote_name,
    int nonblock)
{
  struct ssh_channels *sc = ssh->chanctxt;
  u_int i, found = 0;
  Channel *c;
  int r;

  /* Try to find a free slot where to put the new channel. */
  for (i = 0; i < sc->channels_alloc; i++) {
    if (sc->channels[i] == NULL) {
      /* Found a free slot. */
      found = i;
      break;
    }
  }
  if (i >= sc->channels_alloc) {
    /*
     * There are no free slots. Take last+1 slot and expand
     * the array.
     */
    found = sc->channels_alloc;
    if (sc->channels_alloc > CHANNELS_MAX_CHANNELS)
      fatal_f("internal error: channels_alloc %d too big",
          sc->channels_alloc);
    sc->channels = xrecallocarray(sc->channels, sc->channels_alloc,
        sc->channels_alloc + 10, sizeof(*sc->channels));
    sc->channels_alloc += 10;
    debug2("channel: expanding %d", sc->channels_alloc);
  }
  /* Initialize and return new channel. */
  c = sc->channels[found] = xcalloc(1, sizeof(Channel));
  if ((c->input = sshbuf_new()) == NULL ||
      (c->output = sshbuf_new()) == NULL ||
      (c->extended = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  if ((r = sshbuf_set_max_size(c->input, CHAN_INPUT_MAX)) != 0)
    fatal_fr(r, "sshbuf_set_max_size");
  c->ostate = CHAN_OUTPUT_OPEN;
  c->istate = CHAN_INPUT_OPEN;
  channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, 0);
  c->self = found;
  c->type = type;
  c->ctype = ctype;
  c->local_window = window;
  c->local_window_max = window;
  c->local_maxpacket = maxpack;
  c->remote_name = xstrdup(remote_name);
  c->ctl_chan = -1;
  c->delayed = 1;   /* prevent call to channel_post handler */
  c->inactive_deadline = lookup_timeout(ssh, c->ctype);
  TAILQ_INIT(&c->status_confirms);
  channel_classify(ssh, c);
  debug("channel %d: new %s [%s] (inactive timeout: %f)",
      found, c->ctype, remote_name, c->inactive_deadline != 0.0 ?
      c->inactive_deadline : sc->global_deadline);
  return c;
}

void
channel_set_tty(struct ssh *ssh, Channel *c)
{
  c->remote_has_tty = 1;
  channel_classify(ssh, c);
}

int
channel_close_fd(struct ssh *ssh, Channel *c, int *fdp)
{
  int ret, fd = *fdp;

  if (fd == -1)
    return 0;

  /* restore blocking */
  if (*fdp == c->rfd &&
      (c->restore_block & CHANNEL_RESTORE_RFD) != 0)
    (void)fcntl(*fdp, F_SETFL, c->restore_flags[0]);
  else if (*fdp == c->wfd &&
      (c->restore_block & CHANNEL_RESTORE_WFD) != 0)
    (void)fcntl(*fdp, F_SETFL, c->restore_flags[1]);
  else if (*fdp == c->efd &&
      (c->restore_block & CHANNEL_RESTORE_EFD) != 0)
    (void)fcntl(*fdp, F_SETFL, c->restore_flags[2]);

  if (*fdp == c->rfd) {
    c->io_want &= ~SSH_CHAN_IO_RFD;
    c->io_ready &= ~SSH_CHAN_IO_RFD;
    c->rfd = -1;
    c->pfds[0] = -1;
  }
  if (*fdp == c->wfd) {
    c->io_want &= ~SSH_CHAN_IO_WFD;
    c->io_ready &= ~SSH_CHAN_IO_WFD;
    c->wfd = -1;
    c->pfds[1] = -1;
  }
  if (*fdp == c->efd) {
    c->io_want &= ~SSH_CHAN_IO_EFD;
    c->io_ready &= ~SSH_CHAN_IO_EFD;
    c->efd = -1;
    c->pfds[2] = -1;
  }
  if (*fdp == c->sock) {
    c->io_want &= ~SSH_CHAN_IO_SOCK;
    c->io_ready &= ~SSH_CHAN_IO_SOCK;
    c->sock = -1;
    c->pfds[3] = -1;
  }

  ret = close(fd);
  *fdp = -1; /* probably redundant */
  return ret;
}

/* Close all channel fd/socket. */
static void
channel_close_fds(struct ssh *ssh, Channel *c)
{
  int sock = c->sock, rfd = c->rfd, wfd = c->wfd, efd = c->efd;

  channel_close_fd(ssh, c, &c->sock);
  if (rfd != sock)
    channel_close_fd(ssh, c, &c->rfd);
  if (wfd != sock && wfd != rfd)
    channel_close_fd(ssh, c, &c->wfd);
  if (efd != sock && efd != rfd && efd != wfd)
    channel_close_fd(ssh, c, &c->efd);
}

static void
fwd_perm_clear(struct permission *perm)
{
  free(perm->host_to_connect);
  free(perm->listen_host);
  free(perm->listen_path);
  memset(perm, 0, sizeof(*perm));
}

/* Returns an printable name for the specified forwarding permission list */
static const char *
fwd_ident(int who, int where)
{
  if (who == FORWARD_ADM) {
    if (where == FORWARD_LOCAL)
      return "admin local";
    else if (where == FORWARD_REMOTE)
      return "admin remote";
  } else if (who == FORWARD_USER) {
    if (where == FORWARD_LOCAL)
      return "user local";
    else if (where == FORWARD_REMOTE)
      return "user remote";
  }
  fatal("Unknown forward permission list %d/%d", who, where);
}

/* Returns the forwarding permission list for the specified direction */
static struct permission_set *
permission_set_get(struct ssh *ssh, int where)
{
  struct ssh_channels *sc = ssh->chanctxt;

  switch (where) {
  case FORWARD_LOCAL:
    return &sc->local_perms;
    break;
  case FORWARD_REMOTE:
    return &sc->remote_perms;
    break;
  default:
    fatal_f("invalid forwarding direction %d", where);
  }
}

/* Returns pointers to the specified forwarding list and its element count */
static void
permission_set_get_array(struct ssh *ssh, int who, int where,
    struct permission ***permpp, u_int **npermpp)
{
  struct permission_set *pset = permission_set_get(ssh, where);

  switch (who) {
  case FORWARD_USER:
    *permpp = &pset->permitted_user;
    *npermpp = &pset->num_permitted_user;
    break;
  case FORWARD_ADM:
    *permpp = &pset->permitted_admin;
    *npermpp = &pset->num_permitted_admin;
    break;
  default:
    fatal_f("invalid forwarding client %d", who);
  }
}

/* Adds an entry to the specified forwarding list */
static int
permission_set_add(struct ssh *ssh, int who, int where,
    const char *host_to_connect, int port_to_connect,
    const char *listen_host, const char *listen_path, int listen_port,
    Channel *downstream)
{
  struct permission **permp;
  u_int n, *npermp;

  permission_set_get_array(ssh, who, where, &permp, &npermp);

  if (*npermp >= INT_MAX)
    fatal_f("%s overflow", fwd_ident(who, where));

  *permp = xrecallocarray(*permp, *npermp, *npermp + 1, sizeof(**permp));
  n = (*npermp)++;
#define MAYBE_DUP(s) ((s == NULL) ? NULL : xstrdup(s))
  (*permp)[n].host_to_connect = MAYBE_DUP(host_to_connect);
  (*permp)[n].port_to_connect = port_to_connect;
  (*permp)[n].listen_host = MAYBE_DUP(listen_host);
  (*permp)[n].listen_path = MAYBE_DUP(listen_path);
  (*permp)[n].listen_port = listen_port;
  (*permp)[n].downstream = downstream;
#undef MAYBE_DUP
  return (int)n;
}

static void
mux_remove_remote_forwardings(struct ssh *ssh, Channel *c)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  struct permission *perm;
  int r;
  u_int i;

  for (i = 0; i < pset->num_permitted_user; i++) {
    perm = &pset->permitted_user[i];
    if (perm->downstream != c)
      continue;

    /* cancel on the server, since mux client is gone */
    debug("channel %d: cleanup remote forward for %s:%u",
        c->self, perm->listen_host, perm->listen_port);
    if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
        (r = sshpkt_put_cstring(ssh,
        "cancel-tcpip-forward")) != 0 ||
        (r = sshpkt_put_u8(ssh, 0)) != 0 ||
        (r = sshpkt_put_cstring(ssh,
        channel_rfwd_bind_host(perm->listen_host))) != 0 ||
        (r = sshpkt_put_u32(ssh, perm->listen_port)) != 0 ||
        (r = sshpkt_send(ssh)) != 0) {
      fatal_fr(r, "channel %i", c->self);
    }
    fwd_perm_clear(perm); /* unregister */
  }
}

/* Free the channel and close its fd/socket. */
void
channel_free(struct ssh *ssh, Channel *c)
{
  struct ssh_channels *sc = ssh->chanctxt;
  char *s;
  u_int i, n;
  Channel *other;
  struct channel_confirm *cc;

  for (n = 0, i = 0; i < sc->channels_alloc; i++) {
    if ((other = sc->channels[i]) == NULL)
      continue;
    n++;
    /* detach from mux client and prepare for closing */
    if (c->type == SSH_CHANNEL_MUX_CLIENT &&
        other->type == SSH_CHANNEL_MUX_PROXY &&
        other->mux_ctx == c) {
      other->mux_ctx = NULL;
      other->type = SSH_CHANNEL_OPEN;
      other->istate = CHAN_INPUT_CLOSED;
      other->ostate = CHAN_OUTPUT_CLOSED;
    }
  }
  debug("channel %d: free: %s, nchannels %u", c->self,
      c->remote_name ? c->remote_name : "???", n);

  if (c->type == SSH_CHANNEL_MUX_CLIENT) {
    mux_remove_remote_forwardings(ssh, c);
    free(c->mux_ctx);
    c->mux_ctx = NULL;
  } else if (c->type == SSH_CHANNEL_MUX_LISTENER) {
    free(c->mux_ctx);
    c->mux_ctx = NULL;
  }

  if (log_level_get() >= SYSLOG_LEVEL_DEBUG3) {
    s = channel_open_message(ssh);
    debug3("channel %d: status: %s", c->self, s);
    free(s);
  }

  channel_close_fds(ssh, c);
  sshbuf_free(c->input);
  sshbuf_free(c->output);
  sshbuf_free(c->extended);
  c->input = c->output = c->extended = NULL;
  free(c->remote_name);
  c->remote_name = NULL;
  free(c->path);
  c->path = NULL;
  free(c->listening_addr);
  c->listening_addr = NULL;
  free(c->xctype);
  c->xctype = NULL;
  channel_free_connect_ctx(c);
  while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
    if (cc->abandon_cb != NULL)
      cc->abandon_cb(ssh, c, cc->ctx);
    TAILQ_REMOVE(&c->status_confirms, cc, entry);
    freezero(cc, sizeof(*cc));
  }
  if (c->filter_cleanup != NULL && c->filter_ctx != NULL)
    c->filter_cleanup(ssh, c->self, c->filter_ctx);
  sc->channels[c->self] = NULL;
  freezero(c, sizeof(*c));
}

void
channel_free_all(struct ssh *ssh)
{
  u_int i;
  struct ssh_channels *sc = ssh->chanctxt;

  for (i = 0; i < sc->channels_alloc; i++)
    if (sc->channels[i] != NULL)
      channel_free(ssh, sc->channels[i]);

  free(sc->channels);
  sc->channels = NULL;
  sc->channels_alloc = 0;

  free(sc->x11_saved_display);
  sc->x11_saved_display = NULL;

  free(sc->x11_saved_proto);
  sc->x11_saved_proto = NULL;

  free(sc->x11_saved_data);
  sc->x11_saved_data = NULL;
  sc->x11_saved_data_len = 0;

  free(sc->x11_fake_data);
  sc->x11_fake_data = NULL;
  sc->x11_fake_data_len = 0;
}

void
channel_free_channels(struct ssh *ssh)
{
  struct ssh_channels *sc;

  if (ssh == NULL || ssh->chanctxt == NULL)
    return;
  channel_free_all(ssh);
  channel_clear_permission(ssh, FORWARD_USER, FORWARD_LOCAL);
  channel_clear_permission(ssh, FORWARD_USER, FORWARD_REMOTE);
  channel_clear_permission(ssh, FORWARD_ADM, FORWARD_LOCAL);
  channel_clear_permission(ssh, FORWARD_ADM, FORWARD_REMOTE);
  sc = ssh->chanctxt;
  free(sc->bulk_classifier_tty);
  free(sc->bulk_classifier_notty);
  free(sc->channel_pre);
  free(sc->channel_post);
  freezero(sc, sizeof(*sc));
  ssh->chanctxt = NULL;
}

/*
 * Closes the sockets/fds of all channels.  This is used to close extra file
 * descriptors after a fork.
 */
void
channel_close_all(struct ssh *ssh)
{
  u_int i;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++)
    if (ssh->chanctxt->channels[i] != NULL)
      channel_close_fds(ssh, ssh->chanctxt->channels[i]);
}

/*
 * Stop listening to channels.
 */
void
channel_stop_listening(struct ssh *ssh)
{
  u_int i;
  Channel *c;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c != NULL) {
      switch (c->type) {
      case SSH_CHANNEL_AUTH_SOCKET:
      case SSH_CHANNEL_PORT_LISTENER:
      case SSH_CHANNEL_RPORT_LISTENER:
      case SSH_CHANNEL_X11_LISTENER:
      case SSH_CHANNEL_UNIX_LISTENER:
      case SSH_CHANNEL_RUNIX_LISTENER:
        channel_close_fd(ssh, c, &c->sock);
        channel_free(ssh, c);
        break;
      }
    }
  }
}

/*
 * Returns true if no channel has too much buffered data, and false if one or
 * more channel is overfull.
 */
int
channel_not_very_much_buffered_data(struct ssh *ssh)
{
  u_int i;
  u_int maxsize = ssh_packet_get_maxsize(ssh);
  Channel *c;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_OPEN)
      continue;
    if (sshbuf_len(c->output) > maxsize) {
      debug2("channel %d: big output buffer %zu > %u",
          c->self, sshbuf_len(c->output), maxsize);
      return 0;
    }
  }
  return 1;
}

/* Returns true if any channel is still open. */
int
channel_still_open(struct ssh *ssh)
{
  u_int i;
  Channel *c;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL)
      continue;
    switch (c->type) {
    case SSH_CHANNEL_X11_LISTENER:
    case SSH_CHANNEL_PORT_LISTENER:
    case SSH_CHANNEL_RPORT_LISTENER:
    case SSH_CHANNEL_MUX_LISTENER:
    case SSH_CHANNEL_CLOSED:
    case SSH_CHANNEL_AUTH_SOCKET:
    case SSH_CHANNEL_DYNAMIC:
    case SSH_CHANNEL_RDYNAMIC_OPEN:
    case SSH_CHANNEL_CONNECTING:
    case SSH_CHANNEL_ZOMBIE:
    case SSH_CHANNEL_ABANDONED:
    case SSH_CHANNEL_UNIX_LISTENER:
    case SSH_CHANNEL_RUNIX_LISTENER:
      continue;
    case SSH_CHANNEL_LARVAL:
      continue;
    case SSH_CHANNEL_OPENING:
    case SSH_CHANNEL_OPEN:
    case SSH_CHANNEL_RDYNAMIC_FINISH:
    case SSH_CHANNEL_X11_OPEN:
    case SSH_CHANNEL_MUX_CLIENT:
    case SSH_CHANNEL_MUX_PROXY:
      return 1;
    default:
      fatal_f("bad channel type %d", c->type);
      /* NOTREACHED */
    }
  }
  return 0;
}

/* Returns true if a channel with a TTY is open. */
int
channel_tty_open(struct ssh *ssh)
{
  u_int i;
  Channel *c;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_OPEN)
      continue;
    if (c->client_tty)
      return 1;
  }
  return 0;
}

/* Returns the id of an open channel suitable for keepaliving */
int
channel_find_open(struct ssh *ssh)
{
  u_int i;
  Channel *c;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL || !c->have_remote_id)
      continue;
    switch (c->type) {
    case SSH_CHANNEL_CLOSED:
    case SSH_CHANNEL_DYNAMIC:
    case SSH_CHANNEL_RDYNAMIC_OPEN:
    case SSH_CHANNEL_RDYNAMIC_FINISH:
    case SSH_CHANNEL_X11_LISTENER:
    case SSH_CHANNEL_PORT_LISTENER:
    case SSH_CHANNEL_RPORT_LISTENER:
    case SSH_CHANNEL_MUX_LISTENER:
    case SSH_CHANNEL_MUX_CLIENT:
    case SSH_CHANNEL_MUX_PROXY:
    case SSH_CHANNEL_OPENING:
    case SSH_CHANNEL_CONNECTING:
    case SSH_CHANNEL_ZOMBIE:
    case SSH_CHANNEL_ABANDONED:
    case SSH_CHANNEL_UNIX_LISTENER:
    case SSH_CHANNEL_RUNIX_LISTENER:
      continue;
    case SSH_CHANNEL_LARVAL:
    case SSH_CHANNEL_AUTH_SOCKET:
    case SSH_CHANNEL_OPEN:
    case SSH_CHANNEL_X11_OPEN:
      return i;
    default:
      fatal_f("bad channel type %d", c->type);
      /* NOTREACHED */
    }
  }
  return -1;
}

/* Returns the state of the channel's extended usage flag */
const char *
channel_format_extended_usage(const Channel *c)
{
  if (c->efd == -1)
    return "closed";

  switch (c->extended_usage) {
  case CHAN_EXTENDED_WRITE:
    return "write";
  case CHAN_EXTENDED_READ:
    return "read";
  case CHAN_EXTENDED_IGNORE:
    return "ignore";
  default:
    return "UNKNOWN";
  }
}

static char *
channel_format_status(const Channel *c)
{
  char *ret = NULL;

  xasprintf(&ret, "t%d [%s] %s%u %s%u i%u/%zu o%u/%zu e[%s]/%zu "
      "fd %d/%d/%d sock %d cc %d %s%u io 0x%02x/0x%02x %s%s",
      c->type, c->xctype != NULL ? c->xctype : c->ctype,
      c->have_remote_id ? "r" : "nr", c->remote_id,
      c->mux_ctx != NULL ? "m" : "nm", c->mux_downstream_id,
      c->istate, sshbuf_len(c->input),
      c->ostate, sshbuf_len(c->output),
      channel_format_extended_usage(c), sshbuf_len(c->extended),
      c->rfd, c->wfd, c->efd, c->sock, c->ctl_chan,
      c->have_ctl_child_id ? "c" : "nc", c->ctl_child_id,
      c->io_want, c->io_ready,
      c->isatty ? "T" : (c->remote_has_tty ? "RT" : ""),
      c->bulk ? "B" : "I");
  return ret;
}

/*
 * Returns a message describing the currently open forwarded connections,
 * suitable for sending to the client.  The message contains crlf pairs for
 * newlines.
 */
char *
channel_open_message(struct ssh *ssh)
{
  struct sshbuf *buf;
  Channel *c;
  u_int i;
  int r;
  char *cp, *ret;

  if ((buf = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new");
  if ((r = sshbuf_putf(buf,
      "The following connections are open:\r\n")) != 0)
    fatal_fr(r, "sshbuf_putf");
  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL)
      continue;
    switch (c->type) {
    case SSH_CHANNEL_X11_LISTENER:
    case SSH_CHANNEL_PORT_LISTENER:
    case SSH_CHANNEL_RPORT_LISTENER:
    case SSH_CHANNEL_CLOSED:
    case SSH_CHANNEL_AUTH_SOCKET:
    case SSH_CHANNEL_ZOMBIE:
    case SSH_CHANNEL_ABANDONED:
    case SSH_CHANNEL_MUX_LISTENER:
    case SSH_CHANNEL_UNIX_LISTENER:
    case SSH_CHANNEL_RUNIX_LISTENER:
      continue;
    case SSH_CHANNEL_LARVAL:
    case SSH_CHANNEL_OPENING:
    case SSH_CHANNEL_CONNECTING:
    case SSH_CHANNEL_DYNAMIC:
    case SSH_CHANNEL_RDYNAMIC_OPEN:
    case SSH_CHANNEL_RDYNAMIC_FINISH:
    case SSH_CHANNEL_OPEN:
    case SSH_CHANNEL_X11_OPEN:
    case SSH_CHANNEL_MUX_PROXY:
    case SSH_CHANNEL_MUX_CLIENT:
      cp = channel_format_status(c);
      if ((r = sshbuf_putf(buf, "  #%d %.300s (%s)\r\n",
          c->self, c->remote_name, cp)) != 0) {
        free(cp);
        fatal_fr(r, "sshbuf_putf");
      }
      free(cp);
      continue;
    default:
      fatal_f("bad channel type %d", c->type);
      /* NOTREACHED */
    }
  }
  if ((ret = sshbuf_dup_string(buf)) == NULL)
    fatal_f("sshbuf_dup_string");
  sshbuf_free(buf);
  return ret;
}

void
channel_report_open(struct ssh *ssh, int level)
{
  char *open, *oopen, *cp, ident[256];

  sshpkt_fmt_connection_id(ssh, ident, sizeof(ident));
  do_log2(level, "Connection: %s (pid %ld)", ident, (long)getpid());
  open = oopen = channel_open_message(ssh);
  while ((cp = strsep(&open, "\r\n")) != NULL) {
    if (*cp != '\0')
      do_log2(level, "%s", cp);
  }
  free(oopen);
}

static void
open_preamble(struct ssh *ssh, const char *where, Channel *c, const char *type)
{
  int r;

  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN)) != 0 ||
      (r = sshpkt_put_cstring(ssh, type)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0) {
    fatal_r(r, "%s: channel %i: open", where, c->self);
  }
}

void
channel_send_open(struct ssh *ssh, int id)
{
  Channel *c = channel_lookup(ssh, id);
  int r;

  if (c == NULL) {
    logit("channel_send_open: %d: bad id", id);
    return;
  }
  debug2("channel %d: send open", id);
  open_preamble(ssh, __func__, c, c->ctype);
  if ((r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i", c->self);
}

void
channel_request_start(struct ssh *ssh, int id, const char *service,
    int wantconfirm)
{
  Channel *c = channel_lookup(ssh, id);
  int r;

  if (c == NULL) {
    logit_f("%d: unknown channel id", id);
    return;
  }
  if (!c->have_remote_id)
    fatal_f("channel %d: no remote id", c->self);

  debug2("channel %d: request %s confirm %d", id, service, wantconfirm);
  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_REQUEST)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
      (r = sshpkt_put_cstring(ssh, service)) != 0 ||
      (r = sshpkt_put_u8(ssh, wantconfirm)) != 0) {
    fatal_fr(r, "channel %i", c->self);
  }
}

void
channel_register_status_confirm(struct ssh *ssh, int id,
    channel_confirm_cb *cb, channel_confirm_abandon_cb *abandon_cb, void *ctx)
{
  struct channel_confirm *cc;
  Channel *c;

  if ((c = channel_lookup(ssh, id)) == NULL)
    fatal_f("%d: bad id", id);

  cc = xcalloc(1, sizeof(*cc));
  cc->cb = cb;
  cc->abandon_cb = abandon_cb;
  cc->ctx = ctx;
  TAILQ_INSERT_TAIL(&c->status_confirms, cc, entry);
}

void
channel_register_open_confirm(struct ssh *ssh, int id,
    channel_open_fn *fn, void *ctx)
{
  Channel *c = channel_lookup(ssh, id);

  if (c == NULL) {
    logit_f("%d: bad id", id);
    return;
  }
  c->open_confirm = fn;
  c->open_confirm_ctx = ctx;
}

void
channel_register_cleanup(struct ssh *ssh, int id,
    channel_callback_fn *fn, int do_close)
{
  Channel *c = channel_by_id(ssh, id);

  if (c == NULL) {
    logit_f("%d: bad id", id);
    return;
  }
  c->detach_user = fn;
  c->detach_close = do_close;
}

void
channel_cancel_cleanup(struct ssh *ssh, int id)
{
  Channel *c = channel_by_id(ssh, id);

  if (c == NULL) {
    logit_f("%d: bad id", id);
    return;
  }
  c->detach_user = NULL;
  c->detach_close = 0;
}

void
channel_register_filter(struct ssh *ssh, int id, channel_infilter_fn *ifn,
    channel_outfilter_fn *ofn, channel_filter_cleanup_fn *cfn, void *ctx)
{
  Channel *c = channel_lookup(ssh, id);

  if (c == NULL) {
    logit_f("%d: bad id", id);
    return;
  }
  c->input_filter = ifn;
  c->output_filter = ofn;
  c->filter_ctx = ctx;
  c->filter_cleanup = cfn;
}

void
channel_set_fds(struct ssh *ssh, int id, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty, u_int window_max)
{
  Channel *c = channel_lookup(ssh, id);
  int r;

  if (c == NULL || c->type != SSH_CHANNEL_LARVAL)
    fatal("channel_activate for non-larval channel %d.", id);
  if (!c->have_remote_id)
    fatal_f("channel %d: no remote id", c->self);

  channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, is_tty);
  c->type = SSH_CHANNEL_OPEN;
  channel_set_used_time(ssh, c);
  c->local_window = c->local_window_max = window_max;

  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
      (r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i", c->self);
}

static void
channel_pre_listener(struct ssh *ssh, Channel *c)
{
  c->io_want = SSH_CHAN_IO_SOCK_R;
}

static void
channel_pre_connecting(struct ssh *ssh, Channel *c)
{
  debug3("channel %d: waiting for connection", c->self);
  c->io_want = SSH_CHAN_IO_SOCK_W;
}

static void
channel_pre_open(struct ssh *ssh, Channel *c)
{
  c->io_want = 0;
  if (c->istate == CHAN_INPUT_OPEN &&
      c->remote_window > 0 &&
      sshbuf_len(c->input) < c->remote_window &&
      sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
    c->io_want |= SSH_CHAN_IO_RFD;
  if (c->ostate == CHAN_OUTPUT_OPEN ||
      c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
    if (sshbuf_len(c->output) > 0) {
      c->io_want |= SSH_CHAN_IO_WFD;
    } else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
      if (CHANNEL_EFD_OUTPUT_ACTIVE(c))
        debug2("channel %d: "
            "obuf_empty delayed efd %d/(%zu)", c->self,
            c->efd, sshbuf_len(c->extended));
      else
        chan_obuf_empty(ssh, c);
    }
  }
  /** XXX check close conditions, too */
  if (c->efd != -1 && !(c->istate == CHAN_INPUT_CLOSED &&
      c->ostate == CHAN_OUTPUT_CLOSED)) {
    if (c->extended_usage == CHAN_EXTENDED_WRITE &&
        sshbuf_len(c->extended) > 0)
      c->io_want |= SSH_CHAN_IO_EFD_W;
    else if (c->efd != -1 && !(c->flags & CHAN_EOF_SENT) &&
        (c->extended_usage == CHAN_EXTENDED_READ ||
        c->extended_usage == CHAN_EXTENDED_IGNORE) &&
        sshbuf_len(c->extended) < c->remote_window)
      c->io_want |= SSH_CHAN_IO_EFD_R;
  }
  /* XXX: What about efd? races? */
}

/*
 * This is a special state for X11 authentication spoofing.  An opened X11
 * connection (when authentication spoofing is being done) remains in this
 * state until the first packet has been completely read.  The authentication
 * data in that packet is then substituted by the real data if it matches the
 * fake data, and the channel is put into normal mode.
 * XXX All this happens at the client side.
 * Returns: 0 = need more data, -1 = wrong cookie, 1 = ok
 */
static int
x11_open_helper(struct ssh *ssh, struct sshbuf *b)
{
  struct ssh_channels *sc = ssh->chanctxt;
  u_char *ucp;
  u_int proto_len, data_len;

  if (sc->x11_saved_proto == NULL) {
    error("X11 forwarding opened before X11 forwarding requested");
    return -1;
  }

  /* Is this being called after the refusal deadline? */
  if (sc->x11_refuse_time != 0.0 &&
      monotime_double() >= sc->x11_refuse_time) {
    verbose("Rejected X11 connection after ForwardX11Timeout "
        "expired");
    return -1;
  }

  /* Check if the fixed size part of the packet is in buffer. */
  if (sshbuf_len(b) < 12)
    return 0;

  /* Parse the lengths of variable-length fields. */
  ucp = sshbuf_mutable_ptr(b);
  if (ucp[0] == 0x42) { /* Byte order MSB first. */
    proto_len = 256 * ucp[6] + ucp[7];
    data_len = 256 * ucp[8] + ucp[9];
  } else if (ucp[0] == 0x6c) { /* Byte order LSB first. */
    proto_len = ucp[6] + 256 * ucp[7];
    data_len = ucp[8] + 256 * ucp[9];
  } else {
    debug2("Initial X11 packet contains bad byte order byte: 0x%x",
        ucp[0]);
    return -1;
  }

  /* Check if the whole packet is in buffer. */
  if (sshbuf_len(b) <
      12 + ((proto_len + 3) & ~3) + ((data_len + 3) & ~3))
    return 0;

  /* Check if authentication protocol matches. */
  if (proto_len != strlen(sc->x11_saved_proto) ||
      memcmp(ucp + 12, sc->x11_saved_proto, proto_len) != 0) {
    debug2("X11 connection uses different authentication protocol.");
    return -1;
  }
  /* Check if authentication data matches our fake data. */
  if (data_len != sc->x11_fake_data_len ||
      timingsafe_bcmp(ucp + 12 + ((proto_len + 3) & ~3),
    sc->x11_fake_data, sc->x11_fake_data_len) != 0) {
    debug2("X11 auth data does not match fake data.");
    return -1;
  }
  /* Check fake data length */
  if (sc->x11_fake_data_len != sc->x11_saved_data_len) {
    error("X11 fake_data_len %d != saved_data_len %d",
        sc->x11_fake_data_len, sc->x11_saved_data_len);
    return -1;
  }
  /*
   * Received authentication protocol and data match
   * our fake data. Substitute the fake data with real
   * data.
   */
  memcpy(ucp + 12 + ((proto_len + 3) & ~3),
      sc->x11_saved_data, sc->x11_saved_data_len);
  return 1;
}

void
channel_force_close(struct ssh *ssh, Channel *c, int abandon)
{
  debug3_f("channel %d: forcibly closing", c->self);
  if (c->istate == CHAN_INPUT_OPEN)
    chan_read_failed(ssh, c);
  if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
    sshbuf_reset(c->input);
    chan_ibuf_empty(ssh, c);
  }
  if (c->ostate == CHAN_OUTPUT_OPEN ||
      c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
    sshbuf_reset(c->output);
    chan_write_failed(ssh, c);
  }
  if (c->detach_user)
    c->detach_user(ssh, c->self, 1, NULL);
  if (c->efd != -1)
    channel_close_fd(ssh, c, &c->efd);
  if (abandon)
    c->type = SSH_CHANNEL_ABANDONED;
  /* exempt from inactivity timeouts */
  c->inactive_deadline = 0;
  c->lastused = 0;
}

static void
channel_pre_x11_open(struct ssh *ssh, Channel *c)
{
  int ret = x11_open_helper(ssh, c->output);

  /* c->force_drain = 1; */

  if (ret == 1) {
    c->type = SSH_CHANNEL_OPEN;
    channel_set_used_time(ssh, c);
    channel_pre_open(ssh, c);
  } else if (ret == -1) {
    logit("X11 connection rejected because of wrong "
        "authentication.");
    debug2("X11 rejected %d i%d/o%d",
        c->self, c->istate, c->ostate);
    channel_force_close(ssh, c, 0);
  }
}

static void
channel_pre_mux_client(struct ssh *ssh, Channel *c)
{
  c->io_want = 0;
  if (c->istate == CHAN_INPUT_OPEN && !c->mux_pause &&
      sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
    c->io_want |= SSH_CHAN_IO_RFD;
  if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
    /* clear buffer immediately (discard any partial packet) */
    sshbuf_reset(c->input);
    chan_ibuf_empty(ssh, c);
    /* Start output drain. XXX just kill chan? */
    chan_rcvd_oclose(ssh, c);
  }
  if (c->ostate == CHAN_OUTPUT_OPEN ||
      c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
    if (sshbuf_len(c->output) > 0)
      c->io_want |= SSH_CHAN_IO_WFD;
    else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN)
      chan_obuf_empty(ssh, c);
  }
}

static inline int
socks_decode_error(Channel *c, int status, const char *func, const char *msg)
{
  if (status == SSH_ERR_MESSAGE_INCOMPLETE)
    return 0;
  else {
    debug_r(status, "%s: channel %d: decode %s",
        func, c->self, msg);
    return -1;
  }
}

/* try to decode a socks4 header */
static int
channel_decode_socks4(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
  uint8_t socks_ver, socks_cmd, dest_addr[4];
  uint16_t dest_port;
  char *user = NULL, *host = NULL;
  int success = -1, socks4a = 0, r;
  struct sshbuf *b = NULL;

  if (sshbuf_len(input) < 9)
    return 0;

  /* We may not have a complete message, so work on a dup of the buffer */
  if ((b = sshbuf_fromb(input)) == NULL)
    fatal_f("sshbuf_fromb failed");

  debug2("channel %d: decode socks4", c->self);
  if ((r = sshbuf_get_u8(b, &socks_ver)) != 0 ||
      (r = sshbuf_get_u8(b, &socks_cmd)) != 0 ||
      (r = sshbuf_get_u16(b, &dest_port)) != 0 ||
      (r = sshbuf_get(b, &dest_addr, sizeof(dest_addr))) != 0 ||
      (r = sshbuf_get_nulterminated_string(b, 1024, &user, NULL)) != 0) {
    success = socks_decode_error(c, r, __func__, "header");
    goto out;
  }

  /* Is this a SOCKS4A request? (indicated by an address of 0.0.0.x) */
  if (dest_addr[0] == 0 && dest_addr[1] == 0 &&
      dest_addr[2] == 0 && dest_addr[3] != 0) {
    /* If so, then the hostname follows, also nul-terminated */
    if ((r = sshbuf_get_nulterminated_string(b, 1024,
        &host, NULL)) != 0) {
      success = socks_decode_error(c, r, __func__, "host");
      goto out;
    }
    socks4a = 1;
  } else {
    /* Plain SOCKS4 passes an IPv4 binary address; reconstruct */
    xasprintf(&host, "%d.%d.%d.%d",
        dest_addr[0], dest_addr[1], dest_addr[2], dest_addr[3]);
  }

  /* We have a complete SOCKS4 message; consume it from input */
  if ((r = sshbuf_consume_upto_child(input, b)) != 0)
    fatal_fr(r, "channel %d: consume", c->self);

  /* Handle the request */
  debug2("channel %d: %s: user=\"%s\" command=%d destination=[%s]:%d",
      c->self, socks4a ? "SOCKS4A" : "SOCKS4", user, (int)socks_cmd,
      host, dest_port);
  if (socks_cmd != 1) {
    debug("channel %d: cannot handle %s command 0x%02x",
        c->self, socks4a ? "SOCKS4A" : "SOCKS4", socks_cmd);
    goto out;
  }
  free(c->path);
  c->path = host;
  host = NULL; /* transferred */
  c->host_port = dest_port;

  /* Reply to the SOCKS4 client */
  if ((r = sshbuf_put_u8(output, 0)) != 0 || /* vn: 0 for reply */
      (r = sshbuf_put_u8(output, 90)) != 0 || /* cd: req granted */
      (r = sshbuf_put_u16(output, 0)) != 0 || /* port: ignored */
      (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0) /* ignored */
    fatal_fr(r, "channel %d: compose reply", c->self);

  /* success */
  success = 1;
 out:
  sshbuf_free(b);
  free(user);
  free(host);
  return success;
}

/* try to decode a socks5 header */
#define SSH_SOCKS5_AUTHDONE 0x1000
#define SSH_SOCKS5_NOAUTH 0x00
#define SSH_SOCKS5_IPV4   0x01
#define SSH_SOCKS5_DOMAIN 0x03
#define SSH_SOCKS5_IPV6   0x04
#define SSH_SOCKS5_CONNECT  0x01
#define SSH_SOCKS5_SUCCESS  0x00

/*
 * Handles SOCKS5 authentication. Note 'b' must be a dup of 'input'
 * Returns 0 on insufficient queued date, 1 on authentication success or
 * -1 on error.
 */
static int
channel_socks5_check_auth(Channel *c, struct sshbuf *b, struct sshbuf *input,
    struct sshbuf *output)
{
  uint8_t socks_ver;
  uint8_t nmethods, method;
  int r;
  u_int i, found;

  /* format: ver | nmethods | methods */
  if ((r = sshbuf_get_u8(b, &socks_ver)) != 0)
    return socks_decode_error(c, r, __func__, "version");
  if (socks_ver != 5) /* shouldn't happen; checked by caller^2 */
    fatal_fr(r, "channel %d: internal error: not socks5", c->self);
  if ((r = sshbuf_get_u8(b, &nmethods)) != 0)
    return socks_decode_error(c, r, __func__, "methods");
  for (found = i = 0; i < nmethods; i++) {
    if ((r = sshbuf_get_u8(b, &method)) != 0)
      return socks_decode_error(c, r, __func__, "method");
    if (method == SSH_SOCKS5_NOAUTH)
      found = 1;
  }
  if (!found) {
    debug("channel %d: didn't request SSH_SOCKS5_NOAUTH", c->self);
    return -1;
  }
  /* Consume completed request */
  if ((r = sshbuf_consume_upto_child(input, b)) != 0)
    fatal_fr(r, "channel %d: consume", c->self);

  /* Compose reply: version, method */
  if ((r = sshbuf_put_u8(output, 0x05)) != 0 ||
      (r = sshbuf_put_u8(output, SSH_SOCKS5_NOAUTH)) != 0)
    fatal_fr(r, "channel %d: append reply", c->self);
  /* success */
  debug2("channel %d: socks5 auth done", c->self);
  return 1;
}

static int
channel_decode_socks5(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
  uint8_t socks_ver, socks_cmd, socks_reserved, socks_atyp, addrlen;
  uint16_t dest_port;
  char dest_addr[255+1], ntop[INET6_ADDRSTRLEN];
  u_int af;
  int r, success = -1;;
  struct sshbuf *b = NULL;

  debug2("channel %d: decode socks5 %s", c->self,
      (c->flags & SSH_SOCKS5_AUTHDONE) ? "request" : "auth");

  /* We may not have a complete message, so work on a dup of the buffer */
  if ((b = sshbuf_fromb(input)) == NULL)
    fatal_f("sshbuf_fromb failed");

  if (!(c->flags & SSH_SOCKS5_AUTHDONE)) {
    if ((r = channel_socks5_check_auth(c, b, input, output)) != 1) {
      success = r;
      goto out;
    }
    c->flags |= SSH_SOCKS5_AUTHDONE;
    /* Continue to parse request in case client speculated ahead */
  }

  /* Request messages (auth or connect) always start with the version */
  if ((r = sshbuf_get_u8(b, &socks_ver)) != 0) {
    success = socks_decode_error(c, r, __func__, "version");
    goto out;
  }
  if (socks_ver != 5) /* shouldn't happen */
    fatal_fr(r, "channel %d: internal error: not socks5", c->self);

  /* Parse SOCKS5 request header */
  debug2("channel %d: socks5 post auth", c->self);
  if ((r = sshbuf_get_u8(b, &socks_cmd)) != 0 ||
      (r = sshbuf_get_u8(b, &socks_reserved)) != 0 ||
      (r = sshbuf_get_u8(b, &socks_atyp)) != 0) {
    success = socks_decode_error(c, r, __func__, "request header");
    goto out;
  }

  if (socks_ver != 0x05 ||
      socks_cmd != SSH_SOCKS5_CONNECT ||
      socks_reserved != 0x00) {
    debug2("channel %d: only socks5 connect supported", c->self);
    goto out;
  }

  switch (socks_atyp) {
  case SSH_SOCKS5_IPV4:
    addrlen = 4;
    af = AF_INET;
    break;
  case SSH_SOCKS5_DOMAIN:
    if ((r = sshbuf_get_u8(b, &addrlen)) != 0) {
      success = socks_decode_error(c, r, __func__, "addrlen");
      goto out;
    }
    af = -1;
    break;
  case SSH_SOCKS5_IPV6:
    addrlen = 16;
    af = AF_INET6;
    break;
  default:
    debug2("channel %d: bad socks5 atyp %d", c->self, socks_atyp);
    goto out;
  }
  if ((r = sshbuf_get(b, &dest_addr, addrlen)) != 0 ||
      (r = sshbuf_get_u16(b, &dest_port)) != 0) {
    success = socks_decode_error(c, r, __func__, "addr/port");
    goto out;
  }
  dest_addr[addrlen] = '\0';

  /* We have a complete SOCKS5 request; consume it from input */
  if ((r = sshbuf_consume_upto_child(input, b)) != 0)
    fatal_fr(r, "channel %d: consume", c->self);

  free(c->path);
  c->path = NULL;
  if (socks_atyp == SSH_SOCKS5_DOMAIN)
    c->path = xstrdup(dest_addr);
  else {
    if (inet_ntop(af, dest_addr, ntop, sizeof(ntop)) == NULL)
      return -1;
    c->path = xstrdup(ntop);
  }
  c->host_port = dest_port;

  debug2("channel %d: dynamic request: socks5 host %s port %u command %u",
      c->self, c->path, c->host_port, socks_cmd);

  /* Reply */
  if ((r = sshbuf_put_u8(output, 0x05)) != 0 || /* version */
      (r = sshbuf_put_u8(output, SSH_SOCKS5_SUCCESS)) != 0 || /* cmd */
      (r = sshbuf_put_u8(output, 0)) != 0 || /* reserved, ignored */
      (r = sshbuf_put_u8(output, SSH_SOCKS5_IPV4)) != 0 || /* addrtype */
      (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0 || /* addr */
      (r = sshbuf_put_u16(output, dest_port)) != 0) /* port */
    fatal_fr(r, "channel %d: append reply", c->self);

  /* success */
  success = 1;
 out:
  sshbuf_free(b);
  return success;
}

Channel *
channel_connect_stdio_fwd(struct ssh *ssh,
    const char *host_to_connect, int port_to_connect,
    int in, int out, int nonblock)
{
  Channel *c;

  debug_f("%s:%d", host_to_connect, port_to_connect);

  c = channel_new(ssh, "stdio-forward", SSH_CHANNEL_OPENING, in, out,
      -1, CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
      0, "stdio-forward", nonblock);

  c->path = xstrdup(host_to_connect);
  c->host_port = port_to_connect;
  c->listening_port = 0;
  c->force_drain = 1;

  channel_register_fds(ssh, c, in, out, -1, 0, 1, 0);
  port_open_helper(ssh, c, port_to_connect == PORT_STREAMLOCAL ?
      "direct-streamlocal@openssh.com" : "direct-tcpip");

  return c;
}

/* dynamic port forwarding */
static void
channel_pre_dynamic(struct ssh *ssh, Channel *c)
{
  u_int have;
  u_char ver;
  int r, ret;

  c->io_want = 0;
  have = sshbuf_len(c->input);
  debug2("channel %d: pre_dynamic: have %d", c->self, have);
  /* sshbuf_dump(c->input, stderr); */
  /* check if the fixed size part of the packet is in buffer. */
  if (have < 3) {
    /* need more */
    c->io_want |= SSH_CHAN_IO_RFD;
    return;
  }
  /* try to guess the protocol */
  if ((r = sshbuf_peek_u8(c->input, 0, &ver)) != 0)
    fatal_fr(r, "sshbuf_peek_u8");
  switch (ver) {
  case 0x04:
    ret = channel_decode_socks4(c, c->input, c->output);
    break;
  case 0x05:
    ret = channel_decode_socks5(c, c->input, c->output);
    break;
  default:
    debug2_f("channel %d: unknown SOCKS version %u", c->self, ver);
    ret = -1;
    break;
  }
  if (ret < 0) {
    chan_mark_dead(ssh, c);
  } else if (ret == 0) {
    debug2("channel %d: pre_dynamic: need more", c->self);
    /* need more */
    c->io_want |= SSH_CHAN_IO_RFD;
    if (sshbuf_len(c->output))
      c->io_want |= SSH_CHAN_IO_WFD;
  } else {
    /* switch to the next state */
    c->type = SSH_CHANNEL_OPENING;
    port_open_helper(ssh, c, "direct-tcpip");
  }
}

/* simulate read-error */
static void
rdynamic_close(struct ssh *ssh, Channel *c)
{
  c->type = SSH_CHANNEL_OPEN;
  channel_force_close(ssh, c, 0);
}

/* reverse dynamic port forwarding */
static void
channel_before_prepare_io_rdynamic(struct ssh *ssh, Channel *c)
{
  const u_char *p;
  u_int have, len;
  int r, ret;

  have = sshbuf_len(c->output);
  debug2("channel %d: pre_rdynamic: have %d", c->self, have);
  /* sshbuf_dump(c->output, stderr); */
  /* EOF received */
  if (c->flags & CHAN_EOF_RCVD) {
    if ((r = sshbuf_consume(c->output, have)) != 0)
      fatal_fr(r, "channel %d: consume", c->self);
    rdynamic_close(ssh, c);
    return;
  }
  /* check if the fixed size part of the packet is in buffer. */
  if (have < 3)
    return;
  /* try to guess the protocol */
  p = sshbuf_ptr(c->output);
  switch (p[0]) {
  case 0x04:
    /* switch input/output for reverse forwarding */
    ret = channel_decode_socks4(c, c->output, c->input);
    break;
  case 0x05:
    ret = channel_decode_socks5(c, c->output, c->input);
    break;
  default:
    ret = -1;
    break;
  }
  if (ret < 0) {
    rdynamic_close(ssh, c);
  } else if (ret == 0) {
    debug2("channel %d: pre_rdynamic: need more", c->self);
    /* send socks request to peer */
    len = sshbuf_len(c->input);
    if (len > 0 && len < c->remote_window) {
      if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
          (r = sshpkt_put_stringb(ssh, c->input)) != 0 ||
          (r = sshpkt_send(ssh)) != 0) {
        fatal_fr(r, "channel %i: rdynamic", c->self);
      }
      if ((r = sshbuf_consume(c->input, len)) != 0)
        fatal_fr(r, "channel %d: consume", c->self);
      c->remote_window -= len;
    }
  } else if (rdynamic_connect_finish(ssh, c) < 0) {
    /* the connect failed */
    rdynamic_close(ssh, c);
  }
}

/* This is our fake X11 server socket. */
static void
channel_post_x11_listener(struct ssh *ssh, Channel *c)
{
  Channel *nc;
  struct sockaddr_storage addr;
  int r, newsock, oerrno, remote_port;
  socklen_t addrlen;
  char buf[16384], *remote_ipaddr;

  if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
    return;

  debug("X11 connection requested.");
  addrlen = sizeof(addr);
  newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  if (c->single_connection) {
    oerrno = errno;
    debug2("single_connection: closing X11 listener.");
    channel_close_fd(ssh, c, &c->sock);
    chan_mark_dead(ssh, c);
    errno = oerrno;
  }
  if (newsock == -1) {
    if (errno != EINTR && errno != EWOULDBLOCK &&
        errno != ECONNABORTED)
      error("accept: %.100s", strerror(errno));
    if (errno == EMFILE || errno == ENFILE)
      c->notbefore = monotime_double() + 1.0;
    return;
  }
  set_nodelay(newsock);
  if (ssh->chanctxt->want_tcp_keepalive)
    set_keepalive(newsock); /* logs errors */
  remote_ipaddr = get_peer_ipaddr(newsock);
  remote_port = get_peer_port(newsock);
  snprintf(buf, sizeof buf, "X11 connection from %.200s port %d",
      remote_ipaddr, remote_port);

  nc = channel_new(ssh, "x11-connection",
      SSH_CHANNEL_OPENING, newsock, newsock, -1,
      c->local_window_max, c->local_maxpacket, 0, buf, 1);
  open_preamble(ssh, __func__, nc, "x11");
  if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
      (r = sshpkt_put_u32(ssh, remote_port)) != 0) {
    fatal_fr(r, "channel %i: reply", c->self);
  }
  if ((r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i: send", c->self);
  free(remote_ipaddr);
}

static void
port_open_helper(struct ssh *ssh, Channel *c, char *rtype)
{
  char *local_ipaddr = get_local_ipaddr(c->sock);
  int local_port = c->sock == -1 ? 65536 : get_local_port(c->sock);
  char *remote_ipaddr = get_peer_ipaddr(c->sock);
  int remote_port = get_peer_port(c->sock);
  int r;

  if (remote_port == -1) {
    /* Fake addr/port to appease peers that validate it (Tectia) */
    free(remote_ipaddr);
    remote_ipaddr = xstrdup("127.0.0.1");
    remote_port = 65535;
  }

  free(c->remote_name);
  xasprintf(&c->remote_name,
      "%s: listening port %d for %.100s port %d, "
      "connect from %.200s port %d to %.100s port %d",
      rtype, c->listening_port, c->path, c->host_port,
      remote_ipaddr, remote_port, local_ipaddr, local_port);

  open_preamble(ssh, __func__, c, rtype);
  if (strcmp(rtype, "direct-tcpip") == 0) {
    /* target host, port */
    if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
        (r = sshpkt_put_u32(ssh, c->host_port)) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  } else if (strcmp(rtype, "direct-streamlocal@openssh.com") == 0) {
    /* target path */
    if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  } else if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
    /* listen path */
    if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  } else {
    /* listen address, port */
    if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
        (r = sshpkt_put_u32(ssh, local_port)) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  }
  if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
    /* reserved for future owner/mode info */
    if ((r = sshpkt_put_cstring(ssh, "")) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  } else {
    /* originator host and port */
    if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
        (r = sshpkt_put_u32(ssh, (u_int)remote_port)) != 0)
      fatal_fr(r, "channel %i: reply", c->self);
  }
  if ((r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i: send", c->self);
  free(remote_ipaddr);
  free(local_ipaddr);
}

void
channel_set_x11_refuse_time(struct ssh *ssh, double refuse_time)
{
  ssh->chanctxt->x11_refuse_time = refuse_time;
}

/*
 * This socket is listening for connections to a forwarded TCP/IP port.
 */
static void
channel_post_port_listener(struct ssh *ssh, Channel *c)
{
  Channel *nc;
  struct sockaddr_storage addr;
  int newsock, nextstate;
  socklen_t addrlen;
  char *rtype;

  if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
    return;

  debug("Connection to port %d forwarding to %.100s port %d requested.",
      c->listening_port, c->path, c->host_port);

  if (c->type == SSH_CHANNEL_RPORT_LISTENER) {
    nextstate = SSH_CHANNEL_OPENING;
    rtype = "forwarded-tcpip";
  } else if (c->type == SSH_CHANNEL_RUNIX_LISTENER) {
    nextstate = SSH_CHANNEL_OPENING;
    rtype = "forwarded-streamlocal@openssh.com";
  } else if (c->host_port == PORT_STREAMLOCAL) {
    nextstate = SSH_CHANNEL_OPENING;
    rtype = "direct-streamlocal@openssh.com";
  } else if (c->host_port == 0) {
    nextstate = SSH_CHANNEL_DYNAMIC;
    rtype = "dynamic-tcpip";
  } else {
    nextstate = SSH_CHANNEL_OPENING;
    rtype = "direct-tcpip";
  }

  addrlen = sizeof(addr);
  newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  if (newsock == -1) {
    if (errno != EINTR && errno != EWOULDBLOCK &&
        errno != ECONNABORTED)
      error("accept: %.100s", strerror(errno));
    if (errno == EMFILE || errno == ENFILE)
      c->notbefore = monotime_double() + 1.0;
    return;
  }
  if (addr.ss_family == AF_INET || addr.ss_family == AF_INET6) {
    set_nodelay(newsock);
    if (ssh->chanctxt->want_tcp_keepalive)
      set_keepalive(newsock); /* logs errors */
  }
  nc = channel_new(ssh, rtype, nextstate, newsock, newsock, -1,
      c->local_window_max, c->local_maxpacket, 0, rtype, 1);
  nc->listening_port = c->listening_port;
  nc->host_port = c->host_port;
  if (c->path != NULL)
    nc->path = xstrdup(c->path);

  if (nextstate != SSH_CHANNEL_DYNAMIC)
    port_open_helper(ssh, nc, rtype);
}

/*
 * This is the authentication agent socket listening for connections from
 * clients.
 */
static void
channel_post_auth_listener(struct ssh *ssh, Channel *c)
{
  Channel *nc;
  int r, newsock;
  struct sockaddr_storage addr;
  socklen_t addrlen;

  if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
    return;

  addrlen = sizeof(addr);
  newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
  if (newsock == -1) {
    error("accept from auth socket: %.100s", strerror(errno));
    if (errno == EMFILE || errno == ENFILE)
      c->notbefore = monotime_double() + 1.0;
    return;
  }
  nc = channel_new(ssh, "agent-connection",
      SSH_CHANNEL_OPENING, newsock, newsock, -1,
      c->local_window_max, c->local_maxpacket,
      0, "accepted auth socket", 1);
  open_preamble(ssh, __func__, nc,
      c->agent_new ? "agent-connect" : "auth-agent@openssh.com");
  if ((r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i", c->self);
}

static void
channel_post_connecting(struct ssh *ssh, Channel *c)
{
  int err = 0, sock, isopen, r;
  socklen_t sz = sizeof(err);

  if ((c->io_ready & SSH_CHAN_IO_SOCK_W) == 0)
    return;
  if (!c->have_remote_id)
    fatal_f("channel %d: no remote id", c->self);
  if (c->connect_ctx == NULL)
    fatal_f("channel %d: context missing", c->self);

  /* for rdynamic the OPEN_CONFIRMATION has been sent already */
  isopen = (c->type == SSH_CHANNEL_RDYNAMIC_FINISH);

  if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, &err, &sz) == -1) {
    err = errno;
    error("getsockopt SO_ERROR failed");
  }

  if (err == 0) {
    /* Non-blocking connection completed */
    debug("channel %d: connected to %s port %d",
        c->self, c->connect_ctx->host, c->connect_ctx->port);
    channel_free_connect_ctx(c);
    c->type = SSH_CHANNEL_OPEN;
    channel_set_used_time(ssh, c);
    if (isopen) {
      /* no message necessary */
    } else {
      if ((r = sshpkt_start(ssh,
          SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0 ||
          (r = sshpkt_send(ssh)) != 0)
        fatal_fr(r, "channel %i open confirm", c->self);
    }
    return;
  }
  if (err == EINTR || err == EAGAIN || err == EINPROGRESS)
    return;

  /* Non-blocking connection failed */
  debug("channel %d: connection failed: %s", c->self, strerror(err));

  /* Try next address, if any */
  if ((sock = connect_next(ssh, c->connect_ctx)) == -1) {
    /* Exhausted all addresses for this destination */
    error("connect_to %.100s port %d: failed.",
        c->connect_ctx->host, c->connect_ctx->port);
    channel_free_connect_ctx(c);
    if (isopen) {
      rdynamic_close(ssh, c);
    } else {
      if ((r = sshpkt_start(ssh,
          SSH2_MSG_CHANNEL_OPEN_FAILURE)) != 0 ||
          (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
          (r = sshpkt_put_u32(ssh,
          SSH2_OPEN_CONNECT_FAILED)) != 0 ||
          (r = sshpkt_put_cstring(ssh, strerror(err))) != 0 ||
          (r = sshpkt_put_cstring(ssh, "")) != 0 ||
          (r = sshpkt_send(ssh)) != 0)
        fatal_fr(r, "channel %i: failure", c->self);
      chan_mark_dead(ssh, c);
    }
  }

  /* New non-blocking connection in progress */
  close(c->sock);
  c->sock = c->rfd = c->wfd = sock;
}

static int
channel_handle_rfd(struct ssh *ssh, Channel *c)
{
  char buf[CHAN_RBUF];
  ssize_t len;
  int r, force;
  size_t nr = 0, have, avail, maxlen = CHANNEL_MAX_READ;
  int pty_zeroread = 0;

#ifdef PTY_ZEROREAD
  /* Bug on AIX: read(1) can return 0 for a non-closed fd */
  pty_zeroread = c->isatty;
#endif

  force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;

  if (!force && (c->io_ready & SSH_CHAN_IO_RFD) == 0)
    return 1;
  if ((avail = sshbuf_avail(c->input)) == 0)
    return 1; /* Shouldn't happen */

  /*
   * For "simple" channels (i.e. not datagram or filtered), we can
   * read directly to the channel buffer.
   */
  if (!pty_zeroread && c->input_filter == NULL && !c->datagram) {
    /* Only OPEN channels have valid rwin */
    if (c->type == SSH_CHANNEL_OPEN) {
      if ((have = sshbuf_len(c->input)) >= c->remote_window)
        return 1; /* shouldn't happen */
      if (maxlen > c->remote_window - have)
        maxlen = c->remote_window - have;
    }
    if (maxlen > avail)
      maxlen = avail;
    if ((r = sshbuf_read(c->rfd, c->input, maxlen, &nr)) != 0) {
      if (errno == EINTR || (!force &&
          (errno == EAGAIN || errno == EWOULDBLOCK)))
        return 1;
      debug2("channel %d: read failed rfd %d maxlen %zu: %s",
          c->self, c->rfd, maxlen, ssh_err(r));
      goto rfail;
    }
    if (nr != 0)
      channel_set_used_time(ssh, c);
    return 1;
  }

  errno = 0;
  len = read(c->rfd, buf, sizeof(buf));
  /* fixup AIX zero-length read with errno set to look more like errors */
  if (pty_zeroread && len == 0 && errno != 0)
    len = -1;
  if (len == -1 && (errno == EINTR ||
      ((errno == EAGAIN || errno == EWOULDBLOCK) && !force)))
    return 1;
  if (len < 0 || (!pty_zeroread && len == 0)) {
    debug2("channel %d: read<=0 rfd %d len %zd: %s",
        c->self, c->rfd, len,
        len == 0 ? "closed" : strerror(errno));
 rfail:
    if (c->type != SSH_CHANNEL_OPEN) {
      debug2("channel %d: not open", c->self);
      chan_mark_dead(ssh, c);
      return -1;
    } else {
      chan_read_failed(ssh, c);
    }
    return -1;
  }
  channel_set_used_time(ssh, c);
  if (c->input_filter != NULL) {
    if (c->input_filter(ssh, c, buf, len) == -1) {
      debug2("channel %d: filter stops", c->self);
      chan_read_failed(ssh, c);
    }
  } else if (c->datagram) {
    if ((r = sshbuf_put_string(c->input, buf, len)) != 0)
      fatal_fr(r, "channel %i: put datagram", c->self);
  } else if ((r = sshbuf_put(c->input, buf, len)) != 0)
    fatal_fr(r, "channel %i: put data", c->self);

  return 1;
}

static int
channel_handle_wfd(struct ssh *ssh, Channel *c)
{
  struct termios tio;
  u_char *data = NULL, *buf; /* XXX const; need filter API change */
  size_t dlen, olen = 0;
  int r, len;

  if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
    return 1;
  if (sshbuf_len(c->output) == 0)
    return 1;

  /* Send buffered output data to the socket. */
  olen = sshbuf_len(c->output);
  if (c->output_filter != NULL) {
    if ((buf = c->output_filter(ssh, c, &data, &dlen)) == NULL) {
      debug2("channel %d: filter stops", c->self);
      if (c->type != SSH_CHANNEL_OPEN)
        chan_mark_dead(ssh, c);
      else
        chan_write_failed(ssh, c);
      return -1;
    }
  } else if (c->datagram) {
    if ((r = sshbuf_get_string(c->output, &data, &dlen)) != 0)
      fatal_fr(r, "channel %i: get datagram", c->self);
    buf = data;
  } else {
    buf = data = sshbuf_mutable_ptr(c->output);
    dlen = sshbuf_len(c->output);
  }

  if (c->datagram) {
    /* ignore truncated writes, datagrams might get lost */
    len = write(c->wfd, buf, dlen);
    free(data);
    if (len == -1 && (errno == EINTR || errno == EAGAIN ||
        errno == EWOULDBLOCK))
      return 1;
    if (len <= 0)
      goto write_fail;
    goto out;
  }

#ifdef _AIX
  /* XXX: Later AIX versions can't push as much data to tty */
  if (c->wfd_isatty)
    dlen = MINIMUM(dlen, 8*1024);
#endif

  len = write(c->wfd, buf, dlen);
  if (len == -1 &&
      (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK))
    return 1;
  if (len <= 0) {
 write_fail:
    if (c->type != SSH_CHANNEL_OPEN) {
      debug2("channel %d: not open", c->self);
      chan_mark_dead(ssh, c);
      return -1;
    } else {
      chan_write_failed(ssh, c);
    }
    return -1;
  }
  channel_set_used_time(ssh, c);
#ifndef BROKEN_TCGETATTR_ICANON
  if (c->isatty && dlen >= 1 && buf[0] != '\r') {
    if (tcgetattr(c->wfd, &tio) == 0 &&
        !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
      /*
       * Simulate echo to reduce the impact of
       * traffic analysis. We need to match the
       * size of a SSH2_MSG_CHANNEL_DATA message
       * (4 byte channel id + buf)
       */
      if ((r = sshpkt_msg_ignore(ssh, 4+len)) != 0 ||
          (r = sshpkt_send(ssh)) != 0)
        fatal_fr(r, "channel %i: ignore", c->self);
    }
  }
#endif /* BROKEN_TCGETATTR_ICANON */
  if ((r = sshbuf_consume(c->output, len)) != 0)
    fatal_fr(r, "channel %i: consume", c->self);
 out:
  c->local_consumed += olen - sshbuf_len(c->output);

  return 1;
}

static int
channel_handle_efd_write(struct ssh *ssh, Channel *c)
{
  int r;
  ssize_t len;

  if ((c->io_ready & SSH_CHAN_IO_EFD_W) == 0)
    return 1;
  if (sshbuf_len(c->extended) == 0)
    return 1;

  len = write(c->efd, sshbuf_ptr(c->extended),
      sshbuf_len(c->extended));
  debug2("channel %d: written %zd to efd %d", c->self, len, c->efd);
  if (len == -1 && (errno == EINTR || errno == EAGAIN ||
      errno == EWOULDBLOCK))
    return 1;
  if (len <= 0) {
    debug2("channel %d: closing write-efd %d", c->self, c->efd);
    channel_close_fd(ssh, c, &c->efd);
  } else {
    if ((r = sshbuf_consume(c->extended, len)) != 0)
      fatal_fr(r, "channel %i: consume", c->self);
    c->local_consumed += len;
    channel_set_used_time(ssh, c);
  }
  return 1;
}

static int
channel_handle_efd_read(struct ssh *ssh, Channel *c)
{
  char buf[CHAN_RBUF];
  ssize_t len;
  int r, force;

  force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;

  if (!force && (c->io_ready & SSH_CHAN_IO_EFD_R) == 0)
    return 1;

  len = read(c->efd, buf, sizeof(buf));
  debug2("channel %d: read %zd from efd %d", c->self, len, c->efd);
  if (len == -1 && (errno == EINTR || ((errno == EAGAIN ||
      errno == EWOULDBLOCK) && !force)))
    return 1;
  if (len <= 0) {
    debug2("channel %d: closing read-efd %d", c->self, c->efd);
    channel_close_fd(ssh, c, &c->efd);
    return 1;
  }
  channel_set_used_time(ssh, c);
  if (c->extended_usage == CHAN_EXTENDED_IGNORE)
    debug3("channel %d: discard efd", c->self);
  else if ((r = sshbuf_put(c->extended, buf, len)) != 0)
    fatal_fr(r, "channel %i: append", c->self);
  return 1;
}

static int
channel_handle_efd(struct ssh *ssh, Channel *c)
{
  if (c->efd == -1)
    return 1;

  /** XXX handle drain efd, too */

  if (c->extended_usage == CHAN_EXTENDED_WRITE)
    return channel_handle_efd_write(ssh, c);
  else if (c->extended_usage == CHAN_EXTENDED_READ ||
      c->extended_usage == CHAN_EXTENDED_IGNORE)
    return channel_handle_efd_read(ssh, c);

  return 1;
}

static int
channel_check_window(struct ssh *ssh, Channel *c)
{
  int r;

  if (c->type == SSH_CHANNEL_OPEN &&
      !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
      ((c->local_window_max - c->local_window >
      c->local_maxpacket*3) ||
      c->local_window < c->local_window_max/2) &&
      c->local_consumed > 0) {
    if (!c->have_remote_id)
      fatal_f("channel %d: no remote id", c->self);
    if ((r = sshpkt_start(ssh,
        SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
        (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
        (r = sshpkt_put_u32(ssh, c->local_consumed)) != 0 ||
        (r = sshpkt_send(ssh)) != 0) {
      fatal_fr(r, "channel %i", c->self);
    }
    debug2("channel %d: window %d sent adjust %d", c->self,
        c->local_window, c->local_consumed);
    c->local_window += c->local_consumed;
    c->local_consumed = 0;
  }
  return 1;
}

static void
channel_post_open(struct ssh *ssh, Channel *c)
{
  channel_handle_rfd(ssh, c);
  channel_handle_wfd(ssh, c);
  channel_handle_efd(ssh, c);
  channel_check_window(ssh, c);
}

static u_int
read_mux(struct ssh *ssh, Channel *c, u_int need)
{
  char buf[CHAN_RBUF];
  ssize_t len;
  u_int rlen;
  int r;

  if (sshbuf_len(c->input) < need) {
    rlen = need - sshbuf_len(c->input);
    len = read(c->rfd, buf, MINIMUM(rlen, CHAN_RBUF));
    if (len == -1 && (errno == EINTR || errno == EAGAIN))
      return sshbuf_len(c->input);
    if (len <= 0) {
      debug2("channel %d: ctl read<=0 rfd %d len %zd",
          c->self, c->rfd, len);
      chan_read_failed(ssh, c);
      return 0;
    } else if ((r = sshbuf_put(c->input, buf, len)) != 0)
      fatal_fr(r, "channel %i: append", c->self);
  }
  return sshbuf_len(c->input);
}

static void
channel_post_mux_client_read(struct ssh *ssh, Channel *c)
{
  u_int need;

  if ((c->io_ready & SSH_CHAN_IO_RFD) == 0)
    return;
  if (c->istate != CHAN_INPUT_OPEN && c->istate != CHAN_INPUT_WAIT_DRAIN)
    return;
  if (c->mux_pause)
    return;

  /*
   * Don't not read past the precise end of packets to
   * avoid disrupting fd passing.
   */
  if (read_mux(ssh, c, 4) < 4) /* read header */
    return;
  /* XXX sshbuf_peek_u32 */
  need = PEEK_U32(sshbuf_ptr(c->input));
#define CHANNEL_MUX_MAX_PACKET  (256 * 1024)
  if (need > CHANNEL_MUX_MAX_PACKET) {
    debug2("channel %d: packet too big %u > %u",
        c->self, CHANNEL_MUX_MAX_PACKET, need);
    chan_rcvd_oclose(ssh, c);
    return;
  }
  if (read_mux(ssh, c, need + 4) < need + 4) /* read body */
    return;
  if (c->mux_rcb(ssh, c) != 0) {
    debug("channel %d: mux_rcb failed", c->self);
    chan_mark_dead(ssh, c);
    return;
  }
}

static void
channel_post_mux_client_write(struct ssh *ssh, Channel *c)
{
  ssize_t len;
  int r;

  if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
    return;
  if (sshbuf_len(c->output) == 0)
    return;

  len = write(c->wfd, sshbuf_ptr(c->output), sshbuf_len(c->output));
  if (len == -1 && (errno == EINTR || errno == EAGAIN))
    return;
  if (len <= 0) {
    chan_mark_dead(ssh, c);
    return;
  }
  if ((r = sshbuf_consume(c->output, len)) != 0)
    fatal_fr(r, "channel %i: consume", c->self);
}

static void
channel_post_mux_client(struct ssh *ssh, Channel *c)
{
  channel_post_mux_client_read(ssh, c);
  channel_post_mux_client_write(ssh, c);
}

static void
channel_post_mux_listener(struct ssh *ssh, Channel *c)
{
  Channel *nc;
  struct sockaddr_storage addr;
  socklen_t addrlen;
  int newsock;
  uid_t euid;
  gid_t egid;

  if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
    return;

  debug("multiplexing control connection");

  /*
   * Accept connection on control socket
   */
  memset(&addr, 0, sizeof(addr));
  addrlen = sizeof(addr);
  if ((newsock = accept(c->sock, (struct sockaddr*)&addr,
      &addrlen)) == -1) {
    error_f("accept: %s", strerror(errno));
    if (errno == EMFILE || errno == ENFILE)
      c->notbefore = monotime_double() + 1.0;
    return;
  }

  if (getpeereid(newsock, &euid, &egid) == -1) {
    error_f("getpeereid failed: %s", strerror(errno));
    close(newsock);
    return;
  }
  if ((euid != 0) && (getuid() != euid)) {
    error("multiplex uid mismatch: peer euid %u != uid %u",
        (u_int)euid, (u_int)getuid());
    close(newsock);
    return;
  }
  nc = channel_new(ssh, "mux-control", SSH_CHANNEL_MUX_CLIENT,
      newsock, newsock, -1, c->local_window_max,
      c->local_maxpacket, 0, "mux-control", 1);
  nc->mux_rcb = c->mux_rcb;
  debug3_f("new mux channel %d fd %d", nc->self, nc->sock);
  /* establish state */
  nc->mux_rcb(ssh, nc);
  /* mux state transitions must not elicit protocol messages */
  nc->flags |= CHAN_LOCAL;
}

static void
channel_handler_init(struct ssh_channels *sc)
{
  chan_fn **pre, **post;

  if ((pre = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*pre))) == NULL ||
      (post = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*post))) == NULL)
    fatal_f("allocation failed");

  pre[SSH_CHANNEL_OPEN] =     &channel_pre_open;
  pre[SSH_CHANNEL_X11_OPEN] =   &channel_pre_x11_open;
  pre[SSH_CHANNEL_PORT_LISTENER] = &channel_pre_listener;
  pre[SSH_CHANNEL_RPORT_LISTENER] = &channel_pre_listener;
  pre[SSH_CHANNEL_UNIX_LISTENER] = &channel_pre_listener;
  pre[SSH_CHANNEL_RUNIX_LISTENER] = &channel_pre_listener;
  pre[SSH_CHANNEL_X11_LISTENER] =   &channel_pre_listener;
  pre[SSH_CHANNEL_AUTH_SOCKET] =   &channel_pre_listener;
  pre[SSH_CHANNEL_CONNECTING] =   &channel_pre_connecting;
  pre[SSH_CHANNEL_DYNAMIC] =   &channel_pre_dynamic;
  pre[SSH_CHANNEL_RDYNAMIC_FINISH] = &channel_pre_connecting;
  pre[SSH_CHANNEL_MUX_LISTENER] =   &channel_pre_listener;
  pre[SSH_CHANNEL_MUX_CLIENT] =   &channel_pre_mux_client;

  post[SSH_CHANNEL_OPEN] =   &channel_post_open;
  post[SSH_CHANNEL_PORT_LISTENER] = &channel_post_port_listener;
  post[SSH_CHANNEL_RPORT_LISTENER] = &channel_post_port_listener;
  post[SSH_CHANNEL_UNIX_LISTENER] = &channel_post_port_listener;
  post[SSH_CHANNEL_RUNIX_LISTENER] = &channel_post_port_listener;
  post[SSH_CHANNEL_X11_LISTENER] = &channel_post_x11_listener;
  post[SSH_CHANNEL_AUTH_SOCKET] =   &channel_post_auth_listener;
  post[SSH_CHANNEL_CONNECTING] =   &channel_post_connecting;
  post[SSH_CHANNEL_DYNAMIC] =   &channel_post_open;
  post[SSH_CHANNEL_RDYNAMIC_FINISH] = &channel_post_connecting;
  post[SSH_CHANNEL_MUX_LISTENER] = &channel_post_mux_listener;
  post[SSH_CHANNEL_MUX_CLIENT] =   &channel_post_mux_client;

  sc->channel_pre = pre;
  sc->channel_post = post;
}

/* gc dead channels */
static void
channel_garbage_collect(struct ssh *ssh, Channel *c)
{
  if (c == NULL)
    return;
  if (c->detach_user != NULL) {
    if (!chan_is_dead(ssh, c, c->detach_close))
      return;

    debug2("channel %d: gc: notify user", c->self);
    c->detach_user(ssh, c->self, 0, NULL);
    /* if we still have a callback */
    if (c->detach_user != NULL)
      return;
    debug2("channel %d: gc: user detached", c->self);
  }
  if (!chan_is_dead(ssh, c, 1))
    return;
  debug2("channel %d: garbage collecting", c->self);
  channel_free(ssh, c);
}

enum channel_table { CHAN_PRE, CHAN_POST };

static void
channel_handler(struct ssh *ssh, int table, struct timespec *timeout)
{
  struct ssh_channels *sc = ssh->chanctxt;
  chan_fn **ftab = table == CHAN_PRE ? sc->channel_pre : sc->channel_post;
  u_int i, oalloc;
  Channel *c;
  double now;

  now = monotime_double();
  for (sc->nbulk = i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
    c = sc->channels[i];
    if (c == NULL)
      continue;
    /* Count open channels in bulk state */
    if (c->type == SSH_CHANNEL_OPEN && c->bulk)
      sc->nbulk++;
    /* Try to keep IO going while rekeying */
    if (ssh_packet_is_rekeying(ssh) && c->type != SSH_CHANNEL_OPEN)
      continue;
    if (c->delayed) {
      if (table == CHAN_PRE)
        c->delayed = 0;
      else
        continue;
    }
    if (ftab[c->type] != NULL) {
      if (table == CHAN_PRE && c->type == SSH_CHANNEL_OPEN &&
          channel_get_expiry(ssh, c) != 0 &&
          now >= channel_get_expiry(ssh, c)) {
        /* channel closed for inactivity */
        double deadline = c->inactive_deadline != 0.0 ?
            c->inactive_deadline : sc->global_deadline;
        verbose("channel %d: closing after %f seconds "
            "of inactivity", c->self, deadline);
        channel_force_close(ssh, c, 1);
      } else if (c->notbefore <= now) {
        /* Run handlers that are not paused. */
        (*ftab[c->type])(ssh, c);
        /* inactivity timeouts must interrupt poll() */
        if (timeout != NULL &&
            c->type == SSH_CHANNEL_OPEN &&
            channel_get_expiry(ssh, c) != 0) {
          ptimeout_deadline_monotime_double(timeout,
              channel_get_expiry(ssh, c));
        }
      } else if (timeout != NULL) {
        /*
         * Arrange for poll() wakeup when channel pause
         * timer expires.
         */
        ptimeout_deadline_monotime_double(timeout,
            c->notbefore);
      }
    }
    channel_garbage_collect(ssh, c);
  }
}

/*
 * Create sockets before preparing IO.
 * This is necessary for things that need to happen after reading
 * the network-input but need to be completed before IO event setup, e.g.
 * because they may create new channels.
 */
static void
channel_before_prepare_io(struct ssh *ssh)
{
  struct ssh_channels *sc = ssh->chanctxt;
  Channel *c;
  u_int i, oalloc;

  for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
    c = sc->channels[i];
    if (c == NULL)
      continue;
    if (c->type == SSH_CHANNEL_RDYNAMIC_OPEN)
      channel_before_prepare_io_rdynamic(ssh, c);
  }
}

static void
dump_channel_poll(const char *func, const char *what, Channel *c,
    u_int pollfd_offset, struct pollfd *pfd)
{
#ifdef DEBUG_CHANNEL_POLL
  debug3("%s: channel %d: %s r%d w%d e%d s%d c->pfds [ %d %d %d %d ] "
      "io_want 0x%02x io_ready 0x%02x pfd[%u].fd=%d "
      "pfd.ev 0x%02x pfd.rev 0x%02x", func, c->self, what,
      c->rfd, c->wfd, c->efd, c->sock,
      c->pfds[0], c->pfds[1], c->pfds[2], c->pfds[3],
      c->io_want, c->io_ready,
      pollfd_offset, pfd->fd, pfd->events, pfd->revents);
#endif
}

/* Prepare pollfd entries for a single channel */
static void
channel_prepare_pollfd(Channel *c, u_int *next_pollfd,
    struct pollfd *pfd, u_int npfd)
{
  u_int ev, p = *next_pollfd;

  if (c == NULL)
    return;
  if (p + 4 > npfd) {
    /* Shouldn't happen */
    fatal_f("channel %d: bad pfd offset %u (max %u)",
        c->self, p, npfd);
  }
  c->pfds[0] = c->pfds[1] = c->pfds[2] = c->pfds[3] = -1;
  /*
   * prepare c->rfd
   *
   * This is a special case, since c->rfd might be the same as
   * c->wfd, c->efd and/or c->sock. Handle those here if they want
   * IO too.
   */
  if (c->rfd != -1) {
    ev = 0;
    if ((c->io_want & SSH_CHAN_IO_RFD) != 0)
      ev |= POLLIN;
    /* rfd == wfd */
    if (c->wfd == c->rfd) {
      if ((c->io_want & SSH_CHAN_IO_WFD) != 0)
        ev |= POLLOUT;
    }
    /* rfd == efd */
    if (c->efd == c->rfd) {
      if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
        ev |= POLLIN;
      if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
        ev |= POLLOUT;
    }
    /* rfd == sock */
    if (c->sock == c->rfd) {
      if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
        ev |= POLLIN;
      if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
        ev |= POLLOUT;
    }
    /* Pack a pfd entry if any event armed for this fd */
    if (ev != 0) {
      c->pfds[0] = p;
      pfd[p].fd = c->rfd;
      pfd[p].events = ev;
      dump_channel_poll(__func__, "rfd", c, p, &pfd[p]);
      p++;
    }
  }
  /* prepare c->wfd if wanting IO and not already handled above */
  if (c->wfd != -1 && c->rfd != c->wfd) {
    ev = 0;
    if ((c->io_want & SSH_CHAN_IO_WFD))
      ev |= POLLOUT;
    /* Pack a pfd entry if any event armed for this fd */
    if (ev != 0) {
      c->pfds[1] = p;
      pfd[p].fd = c->wfd;
      pfd[p].events = ev;
      dump_channel_poll(__func__, "wfd", c, p, &pfd[p]);
      p++;
    }
  }
  /* prepare c->efd if wanting IO and not already handled above */
  if (c->efd != -1 && c->rfd != c->efd) {
    ev = 0;
    if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
      ev |= POLLIN;
    if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
      ev |= POLLOUT;
    /* Pack a pfd entry if any event armed for this fd */
    if (ev != 0) {
      c->pfds[2] = p;
      pfd[p].fd = c->efd;
      pfd[p].events = ev;
      dump_channel_poll(__func__, "efd", c, p, &pfd[p]);
      p++;
    }
  }
  /* prepare c->sock if wanting IO and not already handled above */
  if (c->sock != -1 && c->rfd != c->sock) {
    ev = 0;
    if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
      ev |= POLLIN;
    if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
      ev |= POLLOUT;
    /* Pack a pfd entry if any event armed for this fd */
    if (ev != 0) {
      c->pfds[3] = p;
      pfd[p].fd = c->sock;
      pfd[p].events = ev;
      dump_channel_poll(__func__, "sock", c, p, &pfd[p]);
      p++;
    }
  }
  *next_pollfd = p;
}

/* * Allocate/prepare poll structure */
void
channel_prepare_poll(struct ssh *ssh, struct pollfd **pfdp, u_int *npfd_allocp,
    u_int *npfd_activep, u_int npfd_reserved, struct timespec *timeout)
{
  struct ssh_channels *sc = ssh->chanctxt;
  u_int i, oalloc, p, npfd = npfd_reserved;

  channel_before_prepare_io(ssh); /* might create a new channel */
  /* clear out I/O flags from last poll */
  for (i = 0; i < sc->channels_alloc; i++) {
    if (sc->channels[i] == NULL)
      continue;
    sc->channels[i]->io_want = sc->channels[i]->io_ready = 0;
  }
  /* Allocate 4x pollfd for each channel (rfd, wfd, efd, sock) */
  if (sc->channels_alloc >= (INT_MAX / 4) - npfd_reserved)
    fatal_f("too many channels"); /* shouldn't happen */
  npfd += sc->channels_alloc * 4;
  if (npfd > *npfd_allocp) {
    *pfdp = xrecallocarray(*pfdp, *npfd_allocp,
        npfd, sizeof(**pfdp));
    *npfd_allocp = npfd;
  }
  *npfd_activep = npfd_reserved;
  oalloc = sc->channels_alloc;

  channel_handler(ssh, CHAN_PRE, timeout);

  if (oalloc != sc->channels_alloc) {
    /* shouldn't happen */
    fatal_f("channels_alloc changed during CHAN_PRE "
        "(was %u, now %u)", oalloc, sc->channels_alloc);
  }

  /* Prepare pollfd */
  p = npfd_reserved;
  for (i = 0; i < sc->channels_alloc; i++)
    channel_prepare_pollfd(sc->channels[i], &p, *pfdp, npfd);
  *npfd_activep = p;
}

static void
fd_ready(Channel *c, int p, struct pollfd *pfds, u_int npfd, int fd,
    const char *what, u_int revents_mask, u_int ready)
{
  struct pollfd *pfd = &pfds[p];

  if (fd == -1)
    return;
  if (p == -1 || (u_int)p >= npfd)
    fatal_f("channel %d: bad pfd %d (max %u)", c->self, p, npfd);
  dump_channel_poll(__func__, what, c, p, pfd);
  if (pfd->fd != fd) {
    fatal("channel %d: inconsistent %s fd=%d pollfd[%u].fd %d "
        "r%d w%d e%d s%d", c->self, what, fd, p, pfd->fd,
        c->rfd, c->wfd, c->efd, c->sock);
  }
  if ((pfd->revents & POLLNVAL) != 0) {
    fatal("channel %d: invalid %s pollfd[%u].fd %d r%d w%d e%d s%d",
        c->self, what, p, pfd->fd, c->rfd, c->wfd, c->efd, c->sock);
  }
  if ((pfd->revents & (revents_mask|POLLHUP|POLLERR)) != 0)
    c->io_ready |= ready & c->io_want;
}

/*
 * After poll, perform any appropriate operations for channels which have
 * events pending.
 */
void
channel_after_poll(struct ssh *ssh, struct pollfd *pfd, u_int npfd)
{
  struct ssh_channels *sc = ssh->chanctxt;
  u_int i;
  int p;
  Channel *c;

#ifdef DEBUG_CHANNEL_POLL
  for (p = 0; p < (int)npfd; p++) {
    if (pfd[p].revents == 0)
      continue;
    debug_f("pfd[%u].fd %d rev 0x%04x",
        p, pfd[p].fd, pfd[p].revents);
  }
#endif

  /* Convert pollfd into c->io_ready */
  for (i = 0; i < sc->channels_alloc; i++) {
    c = sc->channels[i];
    if (c == NULL)
      continue;
    /* if rfd is shared with efd/sock then wfd should be too */
    if (c->rfd != -1 && c->wfd != -1 && c->rfd != c->wfd &&
        (c->rfd == c->efd || c->rfd == c->sock)) {
      /* Shouldn't happen */
      fatal_f("channel %d: unexpected fds r%d w%d e%d s%d",
          c->self, c->rfd, c->wfd, c->efd, c->sock);
    }
    c->io_ready = 0;
    /* rfd, potentially shared with wfd, efd and sock */
    if (c->rfd != -1 && (p = c->pfds[0]) != -1) {
      fd_ready(c, p, pfd, npfd, c->rfd,
          "rfd", POLLIN, SSH_CHAN_IO_RFD);
      if (c->rfd == c->wfd) {
        fd_ready(c, p, pfd, npfd, c->wfd,
            "wfd/r", POLLOUT, SSH_CHAN_IO_WFD);
      }
      if (c->rfd == c->efd) {
        fd_ready(c, p, pfd, npfd, c->efd,
            "efdr/r", POLLIN, SSH_CHAN_IO_EFD_R);
        fd_ready(c, p, pfd, npfd, c->efd,
            "efdw/r", POLLOUT, SSH_CHAN_IO_EFD_W);
      }
      if (c->rfd == c->sock) {
        fd_ready(c, p, pfd, npfd, c->sock,
            "sockr/r", POLLIN, SSH_CHAN_IO_SOCK_R);
        fd_ready(c, p, pfd, npfd, c->sock,
            "sockw/r", POLLOUT, SSH_CHAN_IO_SOCK_W);
      }
      dump_channel_poll(__func__, "rfd", c, p, pfd);
    }
    /* wfd */
    if (c->wfd != -1 && c->wfd != c->rfd &&
        (p = c->pfds[1]) != -1) {
      fd_ready(c, p, pfd, npfd, c->wfd,
          "wfd", POLLOUT, SSH_CHAN_IO_WFD);
      dump_channel_poll(__func__, "wfd", c, p, pfd);
    }
    /* efd */
    if (c->efd != -1 && c->efd != c->rfd &&
        (p = c->pfds[2]) != -1) {
      fd_ready(c, p, pfd, npfd, c->efd,
          "efdr", POLLIN, SSH_CHAN_IO_EFD_R);
      fd_ready(c, p, pfd, npfd, c->efd,
          "efdw", POLLOUT, SSH_CHAN_IO_EFD_W);
      dump_channel_poll(__func__, "efd", c, p, pfd);
    }
    /* sock */
    if (c->sock != -1 && c->sock != c->rfd &&
        (p = c->pfds[3]) != -1) {
      fd_ready(c, p, pfd, npfd, c->sock,
          "sockr", POLLIN, SSH_CHAN_IO_SOCK_R);
      fd_ready(c, p, pfd, npfd, c->sock,
          "sockw", POLLOUT, SSH_CHAN_IO_SOCK_W);
      dump_channel_poll(__func__, "sock", c, p, pfd);
    }
  }
  channel_handler(ssh, CHAN_POST, NULL);
}

/*
 * Enqueue data for channels with open or draining c->input.
 * Returns non-zero if a packet was enqueued.
 */
static int
channel_output_poll_input_open(struct ssh *ssh, Channel *c)
{
  size_t len, plen;
  const u_char *pkt;
  int r;

  if ((len = sshbuf_len(c->input)) == 0) {
    if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
      /*
       * input-buffer is empty and read-socket shutdown:
       * tell peer, that we will not send more data:
       * send IEOF.
       * hack for extended data: delay EOF if EFD still
       * in use.
       */
      if (CHANNEL_EFD_INPUT_ACTIVE(c))
        debug2("channel %d: "
            "ibuf_empty delayed efd %d/(%zu)",
            c->self, c->efd, sshbuf_len(c->extended));
      else
        chan_ibuf_empty(ssh, c);
    }
    return 0;
  }

  if (!c->have_remote_id)
    fatal_f("channel %d: no remote id", c->self);

  if (c->datagram) {
    /* Check datagram will fit; drop if not */
    if ((r = sshbuf_get_string_direct(c->input, &pkt, &plen)) != 0)
      fatal_fr(r, "channel %i: get datagram", c->self);
    /*
     * XXX this does tail-drop on the datagram queue which is
     * usually suboptimal compared to head-drop. Better to have
     * backpressure at read time? (i.e. read + discard)
     */
    if (plen > c->remote_window || plen > c->remote_maxpacket) {
      debug("channel %d: datagram too big", c->self);
      return 0;
    }
    /* Enqueue it */
    if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
        (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
        (r = sshpkt_put_string(ssh, pkt, plen)) != 0 ||
        (r = sshpkt_send(ssh)) != 0)
      fatal_fr(r, "channel %i: send datagram", c->self);
    c->remote_window -= plen;
    return 1;
  }

  /* Enqueue packet for buffered data. */
  if (len > c->remote_window)
    len = c->remote_window;
  if (len > c->remote_maxpacket)
    len = c->remote_maxpacket;
  if (len == 0)
    return 0;
  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
      (r = sshpkt_put_string(ssh, sshbuf_ptr(c->input), len)) != 0 ||
      (r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i: send data", c->self);
  if ((r = sshbuf_consume(c->input, len)) != 0)
    fatal_fr(r, "channel %i: consume", c->self);
  c->remote_window -= len;
  return 1;
}

/*
 * Enqueue data for channels with open c->extended in read mode.
 * Returns non-zero if a packet was enqueued.
 */
static int
channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
{
  size_t len;
  int r;

  if ((len = sshbuf_len(c->extended)) == 0)
    return 0;

  debug2("channel %d: rwin %u elen %zu euse %d", c->self,
      c->remote_window, sshbuf_len(c->extended), c->extended_usage);
  if (len > c->remote_window)
    len = c->remote_window;
  if (len > c->remote_maxpacket)
    len = c->remote_maxpacket;
  if (len == 0)
    return 0;
  if (!c->have_remote_id)
    fatal_f("channel %d: no remote id", c->self);
  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
      (r = sshpkt_put_u32(ssh, SSH2_EXTENDED_DATA_STDERR)) != 0 ||
      (r = sshpkt_put_string(ssh, sshbuf_ptr(c->extended), len)) != 0 ||
      (r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "channel %i: data", c->self);
  if ((r = sshbuf_consume(c->extended, len)) != 0)
    fatal_fr(r, "channel %i: consume", c->self);
  c->remote_window -= len;
  debug2("channel %d: sent ext data %zu", c->self, len);
  return 1;
}

/*
 * If there is data to send to the connection, enqueue some of it now.
 * Returns non-zero if data was enqueued.
 */
int
channel_output_poll(struct ssh *ssh)
{
  struct ssh_channels *sc = ssh->chanctxt;
  Channel *c;
  u_int i;
  int ret = 0;

  for (i = 0; i < sc->channels_alloc; i++) {
    c = sc->channels[i];
    if (c == NULL)
      continue;

    /*
     * We are only interested in channels that can have buffered
     * incoming data.
     */
    if (c->type != SSH_CHANNEL_OPEN)
      continue;
    if ((c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD))) {
      /* XXX is this true? */
      debug3("channel %d: will not send data after close",
          c->self);
      continue;
    }

    /* Get the amount of buffered data for this channel. */
    if (c->istate == CHAN_INPUT_OPEN ||
        c->istate == CHAN_INPUT_WAIT_DRAIN)
      ret |= channel_output_poll_input_open(ssh, c);
    /* Send extended data, i.e. stderr */
    if (!(c->flags & CHAN_EOF_SENT) &&
        c->extended_usage == CHAN_EXTENDED_READ)
      ret |= channel_output_poll_extended_read(ssh, c);
  }
  return ret;
}

/* -- mux proxy support  */

/*
 * When multiplexing channel messages for mux clients we have to deal
 * with downstream messages from the mux client and upstream messages
 * from the ssh server:
 * 1) Handling downstream messages is straightforward and happens
 *    in channel_proxy_downstream():
 *    - We forward all messages (mostly) unmodified to the server.
 *    - However, in order to route messages from upstream to the correct
 *      downstream client, we have to replace the channel IDs used by the
 *      mux clients with a unique channel ID because the mux clients might
 *      use conflicting channel IDs.
 *    - so we inspect and change both SSH2_MSG_CHANNEL_OPEN and
 *      SSH2_MSG_CHANNEL_OPEN_CONFIRMATION messages, create a local
 *      SSH_CHANNEL_MUX_PROXY channel and replace the mux clients ID
 *      with the newly allocated channel ID.
 * 2) Upstream messages are received by matching SSH_CHANNEL_MUX_PROXY
 *    channels and processed by channel_proxy_upstream(). The local channel ID
 *    is then translated back to the original mux client ID.
 * 3) In both cases we need to keep track of matching SSH2_MSG_CHANNEL_CLOSE
 *    messages so we can clean up SSH_CHANNEL_MUX_PROXY channels.
 * 4) The SSH_CHANNEL_MUX_PROXY channels also need to closed when the
 *    downstream mux client are removed.
 * 5) Handling SSH2_MSG_CHANNEL_OPEN messages from the upstream server
 *    requires more work, because they are not addressed to a specific
 *    channel. E.g. client_request_forwarded_tcpip() needs to figure
 *    out whether the request is addressed to the local client or a
 *    specific downstream client based on the listen-address/port.
 * 6) Agent and X11-Forwarding have a similar problem and are currently
 *    not supported as the matching session/channel cannot be identified
 *    easily.
 */

/*
 * receive packets from downstream mux clients:
 * channel callback fired on read from mux client, creates
 * SSH_CHANNEL_MUX_PROXY channels and translates channel IDs
 * on channel creation.
 */
int
channel_proxy_downstream(struct ssh *ssh, Channel *downstream)
{
  Channel *c = NULL;
  struct sshbuf *original = NULL, *modified = NULL;
  const u_char *cp;
  char *ctype = NULL, *listen_host = NULL;
  u_char type;
  size_t have;
  int ret = -1, r;
  u_int id, remote_id, listen_port;

  /* sshbuf_dump(downstream->input, stderr); */
  if ((r = sshbuf_get_string_direct(downstream->input, &cp, &have))
      != 0) {
    error_fr(r, "parse");
    return -1;
  }
  if (have < 2) {
    error_f("short message");
    return -1;
  }
  type = cp[1];
  /* skip padlen + type */
  cp += 2;
  have -= 2;
  if (ssh_packet_log_type(type))
    debug3_f("channel %u: down->up: type %u",
        downstream->self, type);

  switch (type) {
  case SSH2_MSG_CHANNEL_OPEN:
    if ((original = sshbuf_from(cp, have)) == NULL ||
        (modified = sshbuf_new()) == NULL) {
      error_f("alloc");
      goto out;
    }
    if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0 ||
        (r = sshbuf_get_u32(original, &id)) != 0) {
      error_fr(r, "parse");
      goto out;
    }
    c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
        -1, -1, -1, 0, 0, 0, ctype, 1);
    c->mux_ctx = downstream;  /* point to mux client */
    c->mux_downstream_id = id;  /* original downstream id */
    if ((r = sshbuf_put_cstring(modified, ctype)) != 0 ||
        (r = sshbuf_put_u32(modified, c->self)) != 0 ||
        (r = sshbuf_putb(modified, original)) != 0) {
      error_fr(r, "compose");
      channel_free(ssh, c);
      goto out;
    }
    break;
  case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
    /*
     * Almost the same as SSH2_MSG_CHANNEL_OPEN, except then we
     * need to parse 'remote_id' instead of 'ctype'.
     */
    if ((original = sshbuf_from(cp, have)) == NULL ||
        (modified = sshbuf_new()) == NULL) {
      error_f("alloc");
      goto out;
    }
    if ((r = sshbuf_get_u32(original, &remote_id)) != 0 ||
        (r = sshbuf_get_u32(original, &id)) != 0) {
      error_fr(r, "parse");
      goto out;
    }
    c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
        -1, -1, -1, 0, 0, 0, "mux-down-connect", 1);
    c->mux_ctx = downstream;  /* point to mux client */
    c->mux_downstream_id = id;
    c->remote_id = remote_id;
    c->have_remote_id = 1;
    if ((r = sshbuf_put_u32(modified, remote_id)) != 0 ||
        (r = sshbuf_put_u32(modified, c->self)) != 0 ||
        (r = sshbuf_putb(modified, original)) != 0) {
      error_fr(r, "compose");
      channel_free(ssh, c);
      goto out;
    }
    break;
  case SSH2_MSG_GLOBAL_REQUEST:
    if ((original = sshbuf_from(cp, have)) == NULL) {
      error_f("alloc");
      goto out;
    }
    if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0) {
      error_fr(r, "parse");
      goto out;
    }
    if (strcmp(ctype, "tcpip-forward") != 0) {
      error_f("unsupported request %s", ctype);
      goto out;
    }
    if ((r = sshbuf_get_u8(original, NULL)) != 0 ||
        (r = sshbuf_get_cstring(original, &listen_host, NULL)) != 0 ||
        (r = sshbuf_get_u32(original, &listen_port)) != 0) {
      error_fr(r, "parse");
      goto out;
    }
    if (listen_port > 65535) {
      error_f("tcpip-forward for %s: bad port %u",
          listen_host, listen_port);
      goto out;
    }
    /* Record that connection to this host/port is permitted. */
    permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL, "<mux>",
        -1, listen_host, NULL, (int)listen_port, downstream);
    break;
  case SSH2_MSG_CHANNEL_CLOSE:
    if (have < 4)
      break;
    remote_id = PEEK_U32(cp);
    if ((c = channel_by_remote_id(ssh, remote_id)) != NULL) {
      if (c->flags & CHAN_CLOSE_RCVD)
        channel_free(ssh, c);
      else
        c->flags |= CHAN_CLOSE_SENT;
    }
    break;
  }
  if (modified) {
    if ((r = sshpkt_start(ssh, type)) != 0 ||
        (r = sshpkt_putb(ssh, modified)) != 0 ||
        (r = sshpkt_send(ssh)) != 0) {
      error_fr(r, "send");
      goto out;
    }
  } else {
    if ((r = sshpkt_start(ssh, type)) != 0 ||
        (r = sshpkt_put(ssh, cp, have)) != 0 ||
        (r = sshpkt_send(ssh)) != 0) {
      error_fr(r, "send");
      goto out;
    }
  }
  ret = 0;
 out:
  free(ctype);
  free(listen_host);
  sshbuf_free(original);
  sshbuf_free(modified);
  return ret;
}

/*
 * receive packets from upstream server and de-multiplex packets
 * to correct downstream:
 * implemented as a helper for channel input handlers,
 * replaces local (proxy) channel ID with downstream channel ID.
 */
int
channel_proxy_upstream(Channel *c, int type, uint32_t seq, struct ssh *ssh)
{
  struct sshbuf *b = NULL;
  Channel *downstream;
  const u_char *cp = NULL;
  size_t len;
  int r;

  /*
   * When receiving packets from the peer we need to check whether we
   * need to forward the packets to the mux client. In this case we
   * restore the original channel id and keep track of CLOSE messages,
   * so we can cleanup the channel.
   */
  if (c == NULL || c->type != SSH_CHANNEL_MUX_PROXY)
    return 0;
  if ((downstream = c->mux_ctx) == NULL)
    return 0;
  switch (type) {
  case SSH2_MSG_CHANNEL_CLOSE:
  case SSH2_MSG_CHANNEL_DATA:
  case SSH2_MSG_CHANNEL_EOF:
  case SSH2_MSG_CHANNEL_EXTENDED_DATA:
  case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
  case SSH2_MSG_CHANNEL_OPEN_FAILURE:
  case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
  case SSH2_MSG_CHANNEL_SUCCESS:
  case SSH2_MSG_CHANNEL_FAILURE:
  case SSH2_MSG_CHANNEL_REQUEST:
    break;
  default:
    debug2_f("channel %u: unsupported type %u", c->self, type);
    return 0;
  }
  if ((b = sshbuf_new()) == NULL) {
    error_f("alloc reply");
    goto out;
  }
  /* get remaining payload (after id) */
  cp = sshpkt_ptr(ssh, &len);
  if (cp == NULL) {
    error_f("no packet");
    goto out;
  }
  /* translate id and send to muxclient */
  if ((r = sshbuf_put_u8(b, 0)) != 0 || /* padlen */
      (r = sshbuf_put_u8(b, type)) != 0 ||
      (r = sshbuf_put_u32(b, c->mux_downstream_id)) != 0 ||
      (r = sshbuf_put(b, cp, len)) != 0 ||
      (r = sshbuf_put_stringb(downstream->output, b)) != 0) {
    error_fr(r, "compose muxclient");
    goto out;
  }
  /* sshbuf_dump(b, stderr); */
  if (ssh_packet_log_type(type))
    debug3_f("channel %u: up->down: type %u", c->self, type);
 out:
  /* update state */
  switch (type) {
  case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
    /* record remote_id for SSH2_MSG_CHANNEL_CLOSE */
    if (cp && len > 4) {
      c->remote_id = PEEK_U32(cp);
      c->have_remote_id = 1;
    }
    break;
  case SSH2_MSG_CHANNEL_CLOSE:
    if (c->flags & CHAN_CLOSE_SENT)
      channel_free(ssh, c);
    else
      c->flags |= CHAN_CLOSE_RCVD;
    break;
  }
  sshbuf_free(b);
  return 1;
}

/* -- protocol input */

/* Parse a channel ID from the current packet */
static int
channel_parse_id(struct ssh *ssh, const char *where, const char *what)
{
  uint32_t id;
  int r;

  if ((r = sshpkt_get_u32(ssh, &id)) != 0) {
    error_r(r, "%s: parse id", where);
    ssh_packet_disconnect(ssh, "Invalid %s message", what);
  }
  if (id > INT_MAX) {
    error_r(r, "%s: bad channel id %u", where, id);
    ssh_packet_disconnect(ssh, "Invalid %s channel id", what);
  }
  return (int)id;
}

/* Lookup a channel from an ID in the current packet */
static Channel *
channel_from_packet_id(struct ssh *ssh, const char *where, const char *what)
{
  int id = channel_parse_id(ssh, where, what);
  Channel *c;

  if ((c = channel_lookup(ssh, id)) == NULL) {
    ssh_packet_disconnect(ssh,
        "%s packet referred to nonexistent channel %d", what, id);
  }
  return c;
}

int
channel_input_data(int type, uint32_t seq, struct ssh *ssh)
{
  const u_char *data;
  size_t data_len, win_len;
  Channel *c = channel_from_packet_id(ssh, __func__, "data");
  int r;

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;

  /* Ignore any data for non-open channels (might happen on close) */
  if (c->type != SSH_CHANNEL_OPEN &&
      c->type != SSH_CHANNEL_RDYNAMIC_OPEN &&
      c->type != SSH_CHANNEL_RDYNAMIC_FINISH &&
      c->type != SSH_CHANNEL_X11_OPEN)
    return 0;

  /* Get the data. */
  if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0)
    fatal_fr(r, "channel %i: get data", c->self);

  win_len = data_len;
  if (c->datagram)
    win_len += 4;  /* string length header */

  /*
   * The sending side reduces its window as it sends data, so we
   * must 'fake' consumption of the data in order to ensure that window
   * updates are sent back. Otherwise the connection might deadlock.
   */
  if (c->ostate != CHAN_OUTPUT_OPEN) {
    if (win_len > c->local_window)
      c->local_window = 0;
    else
      c->local_window -= win_len;
    c->local_consumed += win_len;
    return 0;
  }

  if (win_len > c->local_maxpacket) {
    logit("channel %d: rcvd big packet %zu, maxpack %u",
        c->self, win_len, c->local_maxpacket);
    return 0;
  }
  if (win_len > c->local_window) {
    u_int delta = win_len - c->local_window;

    if (c->local_window_exceeded > UINT_MAX - delta)
      c->local_window_exceeded = UINT_MAX;
    else
      c->local_window_exceeded += delta;
    logit("channel %d: rcvd too much data %zu, win %u/%u "
        "(excess %u)", c->self, win_len, c->local_window,
        c->local_window_max, c->local_window_exceeded);
    c->local_window = 0;
    /* Allow 10% grace before bringing the hammer down */
    if (c->local_window_exceeded > (c->local_window_max / 10)) {
      ssh_packet_disconnect(ssh, "channel %d: peer ignored "
          "channel window", c->self);
    }
  } else {
    c->local_window -= win_len;
    c->local_window_exceeded = 0;
  }

  if (c->datagram) {
    if ((r = sshbuf_put_string(c->output, data, data_len)) != 0)
      fatal_fr(r, "channel %i: append datagram", c->self);
  } else if ((r = sshbuf_put(c->output, data, data_len)) != 0)
    fatal_fr(r, "channel %i: append data", c->self);

  return 0;
}

int
channel_input_extended_data(int type, uint32_t seq, struct ssh *ssh)
{
  const u_char *data;
  size_t data_len;
  uint32_t tcode;
  Channel *c = channel_from_packet_id(ssh, __func__, "extended data");
  int r;

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
  if (c->type != SSH_CHANNEL_OPEN) {
    logit("channel %d: ext data for non open", c->self);
    return 0;
  }
  if (c->flags & CHAN_EOF_RCVD) {
    if (ssh->compat & SSH_BUG_EXTEOF)
      debug("channel %d: accepting ext data after eof",
          c->self);
    else
      ssh_packet_disconnect(ssh, "Received extended_data "
          "after EOF on channel %d.", c->self);
  }

  if ((r = sshpkt_get_u32(ssh, &tcode)) != 0) {
    error_fr(r, "parse tcode");
    ssh_packet_disconnect(ssh, "Invalid extended_data message");
  }
  if (c->efd == -1 ||
      c->extended_usage != CHAN_EXTENDED_WRITE ||
      tcode != SSH2_EXTENDED_DATA_STDERR) {
    logit("channel %d: bad ext data", c->self);
    return 0;
  }
  if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse data");
    ssh_packet_disconnect(ssh, "Invalid extended_data message");
  }

  if (data_len > c->local_window) {
    logit("channel %d: rcvd too much extended_data %zu, win %u",
        c->self, data_len, c->local_window);
    return 0;
  }
  debug2("channel %d: rcvd ext data %zu", c->self, data_len);
  /* XXX sshpkt_getb? */
  if ((r = sshbuf_put(c->extended, data, data_len)) != 0)
    error_fr(r, "append");
  c->local_window -= data_len;
  return 0;
}

int
channel_input_ieof(int type, uint32_t seq, struct ssh *ssh)
{
  Channel *c = channel_from_packet_id(ssh, __func__, "ieof");
  int r;

        if ((r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse data");
    ssh_packet_disconnect(ssh, "Invalid ieof message");
  }

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
  chan_rcvd_ieof(ssh, c);

  /* XXX force input close */
  if (c->force_drain && c->istate == CHAN_INPUT_OPEN) {
    debug("channel %d: FORCE input drain", c->self);
    c->istate = CHAN_INPUT_WAIT_DRAIN;
    if (sshbuf_len(c->input) == 0)
      chan_ibuf_empty(ssh, c);
  }
  return 0;
}

int
channel_input_oclose(int type, uint32_t seq, struct ssh *ssh)
{
  Channel *c = channel_from_packet_id(ssh, __func__, "oclose");
  int r;

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
        if ((r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse data");
    ssh_packet_disconnect(ssh, "Invalid oclose message");
  }
  chan_rcvd_oclose(ssh, c);
  return 0;
}

int
channel_input_open_confirmation(int type, uint32_t seq, struct ssh *ssh)
{
  Channel *c = channel_from_packet_id(ssh, __func__, "open confirmation");
  uint32_t remote_window, remote_maxpacket;
  int r;

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
  if (c->type != SSH_CHANNEL_OPENING)
    ssh_packet_disconnect(ssh, "Received open confirmation for "
        "non-opening channel %d.", c->self);
  /*
   * Record the remote channel number and mark that the channel
   * is now open.
   */
  if ((r = sshpkt_get_u32(ssh, &c->remote_id)) != 0 ||
      (r = sshpkt_get_u32(ssh, &remote_window)) != 0 ||
      (r = sshpkt_get_u32(ssh, &remote_maxpacket)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "window/maxpacket");
    ssh_packet_disconnect(ssh, "Invalid open confirmation message");
  }

  c->have_remote_id = 1;
  c->remote_window = remote_window;
  c->remote_maxpacket = remote_maxpacket;
  c->type = SSH_CHANNEL_OPEN;
  if (c->open_confirm) {
    debug2_f("channel %d: callback start", c->self);
    c->open_confirm(ssh, c->self, 1, c->open_confirm_ctx);
    debug2_f("channel %d: callback done", c->self);
  }
  channel_set_used_time(ssh, c);
  debug2("channel %d: open confirm rwindow %u rmax %u", c->self,
      c->remote_window, c->remote_maxpacket);
  return 0;
}

static char *
reason2txt(int reason)
{
  switch (reason) {
  case SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED:
    return "administratively prohibited";
  case SSH2_OPEN_CONNECT_FAILED:
    return "connect failed";
  case SSH2_OPEN_UNKNOWN_CHANNEL_TYPE:
    return "unknown channel type";
  case SSH2_OPEN_RESOURCE_SHORTAGE:
    return "resource shortage";
  }
  return "unknown reason";
}

int
channel_input_open_failure(int type, uint32_t seq, struct ssh *ssh)
{
  Channel *c = channel_from_packet_id(ssh, __func__, "open failure");
  uint32_t reason;
  char *msg = NULL;
  int r;

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
  if (c->type != SSH_CHANNEL_OPENING)
    ssh_packet_disconnect(ssh, "Received open failure for "
        "non-opening channel %d.", c->self);
  if ((r = sshpkt_get_u32(ssh, &reason)) != 0) {
    error_fr(r, "parse reason");
    ssh_packet_disconnect(ssh, "Invalid open failure message");
  }
  /* skip language */
  if ((r = sshpkt_get_cstring(ssh, &msg, NULL)) != 0 ||
      (r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse msg/lang");
    ssh_packet_disconnect(ssh, "Invalid open failure message");
  }
  logit("channel %d: open failed: %s%s%s", c->self,
      reason2txt(reason), msg ? ": ": "", msg ? msg : "");
  free(msg);
  if (c->open_confirm) {
    debug2_f("channel %d: callback start", c->self);
    c->open_confirm(ssh, c->self, 0, c->open_confirm_ctx);
    debug2_f("channel %d: callback done", c->self);
  }
  /* Schedule the channel for cleanup/deletion. */
  chan_mark_dead(ssh, c);
  return 0;
}

int
channel_input_window_adjust(int type, uint32_t seq, struct ssh *ssh)
{
  int id = channel_parse_id(ssh, __func__, "window adjust");
  Channel *c;
  uint32_t adjust;
  u_int new_rwin;
  int r;

  if ((c = channel_lookup(ssh, id)) == NULL) {
    logit("Received window adjust for non-open channel %d.", id);
    return 0;
  }

  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
  if ((r = sshpkt_get_u32(ssh, &adjust)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse adjust");
    ssh_packet_disconnect(ssh, "Invalid window adjust message");
  }
  debug2("channel %d: rcvd adjust %u", c->self, adjust);
  if ((new_rwin = c->remote_window + adjust) < c->remote_window) {
    fatal("channel %d: adjust %u overflows remote window %u",
        c->self, adjust, c->remote_window);
  }
  c->remote_window = new_rwin;
  return 0;
}

int
channel_input_status_confirm(int type, uint32_t seq, struct ssh *ssh)
{
  int id = channel_parse_id(ssh, __func__, "status confirm");
  Channel *c;
  struct channel_confirm *cc;

  /* Reset keepalive timeout */
  ssh_packet_set_alive_timeouts(ssh, 0);

  debug2_f("type %d id %d", type, id);

  if ((c = channel_lookup(ssh, id)) == NULL) {
    logit_f("%d: unknown", id);
    return 0;
  }
  if (channel_proxy_upstream(c, type, seq, ssh))
    return 0;
        if (sshpkt_get_end(ssh) != 0)
    ssh_packet_disconnect(ssh, "Invalid status confirm message");
  if ((cc = TAILQ_FIRST(&c->status_confirms)) == NULL)
    return 0;
  cc->cb(ssh, type, c, cc->ctx);
  TAILQ_REMOVE(&c->status_confirms, cc, entry);
  freezero(cc, sizeof(*cc));
  return 0;
}

/* -- tcp forwarding */

void
channel_set_af(struct ssh *ssh, int af)
{
  ssh->chanctxt->IPv4or6 = af;
}


/*
 * Determine whether or not a port forward listens to loopback, the
 * specified address or wildcard. On the client, a specified bind
 * address will always override gateway_ports. On the server, a
 * gateway_ports of 1 (``yes'') will override the client's specification
 * and force a wildcard bind, whereas a value of 2 (``clientspecified'')
 * will bind to whatever address the client asked for.
 *
 * Special-case listen_addrs are:
 *
 * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
 * "" (empty string), "*"  -> wildcard v4/v6
 * "localhost"             -> loopback v4/v6
 * "127.0.0.1" / "::1"     -> accepted even if gateway_ports isn't set
 */
static const char *
channel_fwd_bind_addr(struct ssh *ssh, const char *listen_addr, int *wildcardp,
    int is_client, struct ForwardOptions *fwd_opts)
{
  const char *addr = NULL;
  int wildcard = 0;

  if (listen_addr == NULL) {
    /* No address specified: default to gateway_ports setting */
    if (fwd_opts->gateway_ports)
      wildcard = 1;
  } else if (fwd_opts->gateway_ports || is_client) {
    if (((ssh->compat & SSH_OLD_FORWARD_ADDR) &&
        strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
        *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
        (!is_client && fwd_opts->gateway_ports == 1)) {
      wildcard = 1;
      /*
       * Notify client if they requested a specific listen
       * address and it was overridden.
       */
      if (*listen_addr != '\0' &&
          strcmp(listen_addr, "0.0.0.0") != 0 &&
          strcmp(listen_addr, "*") != 0) {
        ssh_packet_send_debug(ssh,
            "Forwarding listen address "
            "\"%s\" overridden by server "
            "GatewayPorts", listen_addr);
      }
    } else if (strcmp(listen_addr, "localhost") != 0 ||
        strcmp(listen_addr, "127.0.0.1") == 0 ||
        strcmp(listen_addr, "::1") == 0) {
      /*
       * Accept explicit localhost address when
       * GatewayPorts=yes. The "localhost" hostname is
       * deliberately skipped here so it will listen on all
       * available local address families.
       */
      addr = listen_addr;
    }
  } else if (strcmp(listen_addr, "127.0.0.1") == 0 ||
      strcmp(listen_addr, "::1") == 0) {
    /*
     * If a specific IPv4/IPv6 localhost address has been
     * requested then accept it even if gateway_ports is in
     * effect. This allows the client to prefer IPv4 or IPv6.
     */
    addr = listen_addr;
  }
  if (wildcardp != NULL)
    *wildcardp = wildcard;
  return addr;
}

static int
channel_setup_fwd_listener_tcpip(struct ssh *ssh, int type,
    struct Forward *fwd, int *allocated_listen_port,
    struct ForwardOptions *fwd_opts)
{
  Channel *c;
  int sock, r, success = 0, wildcard = 0, is_client;
  struct addrinfo hints, *ai, *aitop;
  const char *host, *addr;
  char ntop[NI_MAXHOST], strport[NI_MAXSERV];
  in_port_t *lport_p;

  is_client = (type == SSH_CHANNEL_PORT_LISTENER);

  if (is_client && fwd->connect_path != NULL) {
    host = fwd->connect_path;
  } else {
    host = (type == SSH_CHANNEL_RPORT_LISTENER) ?
        fwd->listen_host : fwd->connect_host;
    if (host == NULL) {
      error("No forward host name.");
      return 0;
    }
    if (strlen(host) >= NI_MAXHOST) {
      error("Forward host name too long.");
      return 0;
    }
  }

  /* Determine the bind address, cf. channel_fwd_bind_addr() comment */
  addr = channel_fwd_bind_addr(ssh, fwd->listen_host, &wildcard,
      is_client, fwd_opts);
  debug3_f("type %d wildcard %d addr %s", type, wildcard,
      (addr == NULL) ? "NULL" : addr);

  /*
   * getaddrinfo returns a loopback address if the hostname is
   * set to NULL and hints.ai_flags is not AI_PASSIVE
   */
  memset(&hints, 0, sizeof(hints));
  hints.ai_family = ssh->chanctxt->IPv4or6;
  hints.ai_flags = wildcard ? AI_PASSIVE : 0;
  hints.ai_socktype = SOCK_STREAM;
  snprintf(strport, sizeof strport, "%d", fwd->listen_port);
  if ((r = getaddrinfo(addr, strport, &hints, &aitop)) != 0) {
    if (addr == NULL) {
      /* This really shouldn't happen */
      ssh_packet_disconnect(ssh, "getaddrinfo: fatal error: %s",
          ssh_gai_strerror(r));
    } else {
      error_f("getaddrinfo(%.64s): %s", addr,
          ssh_gai_strerror(r));
    }
    return 0;
  }
  if (allocated_listen_port != NULL)
    *allocated_listen_port = 0;
  for (ai = aitop; ai; ai = ai->ai_next) {
    switch (ai->ai_family) {
    case AF_INET:
      lport_p = &((struct sockaddr_in *)ai->ai_addr)->
          sin_port;
      break;
    case AF_INET6:
      lport_p = &((struct sockaddr_in6 *)ai->ai_addr)->
          sin6_port;
      break;
    default:
      continue;
    }
    /*
     * If allocating a port for -R forwards, then use the
     * same port for all address families.
     */
    if (type == SSH_CHANNEL_RPORT_LISTENER &&
        fwd->listen_port == 0 && allocated_listen_port != NULL &&
        *allocated_listen_port > 0)
      *lport_p = htons(*allocated_listen_port);

    if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
        strport, sizeof(strport),
        NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
      error_f("getnameinfo failed");
      continue;
    }
    /* Create a port to listen for the host. */
    sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
    if (sock == -1) {
      /* this is no error since kernel may not support ipv6 */
      verbose("socket [%s]:%s: %.100s", ntop, strport,
          strerror(errno));
      continue;
    }

    set_reuseaddr(sock);
    if (ai->ai_family == AF_INET6)
      sock_set_v6only(sock);

    debug("Local forwarding listening on %s port %s.",
        ntop, strport);

    /* Bind the socket to the address. */
    if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
      /*
       * address can be in if use ipv6 address is
       * already bound
       */
      if (!ai->ai_next)
        error("bind [%s]:%s: %.100s",
            ntop, strport, strerror(errno));
      else
        verbose("bind [%s]:%s: %.100s",
            ntop, strport, strerror(errno));

      close(sock);
      continue;
    }
    /* Start listening for connections on the socket. */
    if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
      error("listen [%s]:%s: %.100s", ntop, strport,
          strerror(errno));
      close(sock);
      continue;
    }

    /*
     * fwd->listen_port == 0 requests a dynamically allocated port -
     * record what we got.
     */
    if (type == SSH_CHANNEL_RPORT_LISTENER &&
        fwd->listen_port == 0 &&
        allocated_listen_port != NULL &&
        *allocated_listen_port == 0) {
      *allocated_listen_port = get_local_port(sock);
      debug("Allocated listen port %d",
          *allocated_listen_port);
    }

    /* Allocate a channel number for the socket. */
    c = channel_new(ssh, "port-listener", type, sock, sock, -1,
        CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
        0, "port listener", 1);
    c->path = xstrdup(host);
    c->host_port = fwd->connect_port;
    c->listening_addr = addr == NULL ? NULL : xstrdup(addr);
    if (fwd->listen_port == 0 && allocated_listen_port != NULL &&
        !(ssh->compat & SSH_BUG_DYNAMIC_RPORT))
      c->listening_port = *allocated_listen_port;
    else
      c->listening_port = fwd->listen_port;
    success = 1;
  }
  if (success == 0)
    error_f("cannot listen to port: %d", fwd->listen_port);
  freeaddrinfo(aitop);
  return success;
}

static int
channel_setup_fwd_listener_streamlocal(struct ssh *ssh, int type,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
  struct sockaddr_un sunaddr;
  const char *path;
  Channel *c;
  int port, sock;
  mode_t omask;

  switch (type) {
  case SSH_CHANNEL_UNIX_LISTENER:
    if (fwd->connect_path != NULL) {
      if (strlen(fwd->connect_path) > sizeof(sunaddr.sun_path)) {
        error("Local connecting path too long: %s",
            fwd->connect_path);
        return 0;
      }
      path = fwd->connect_path;
      port = PORT_STREAMLOCAL;
    } else {
      if (fwd->connect_host == NULL) {
        error("No forward host name.");
        return 0;
      }
      if (strlen(fwd->connect_host) >= NI_MAXHOST) {
        error("Forward host name too long.");
        return 0;
      }
      path = fwd->connect_host;
      port = fwd->connect_port;
    }
    break;
  case SSH_CHANNEL_RUNIX_LISTENER:
    path = fwd->listen_path;
    port = PORT_STREAMLOCAL;
    break;
  default:
    error_f("unexpected channel type %d", type);
    return 0;
  }

  if (fwd->listen_path == NULL) {
    error("No forward path name.");
    return 0;
  }
  if (strlen(fwd->listen_path) > sizeof(sunaddr.sun_path)) {
    error("Local listening path too long: %s", fwd->listen_path);
    return 0;
  }

  debug3_f("type %d path %s", type, fwd->listen_path);

  /* Start a Unix domain listener. */
  omask = umask(fwd_opts->streamlocal_bind_mask);
  sock = unix_listener(fwd->listen_path, SSH_LISTEN_BACKLOG,
      fwd_opts->streamlocal_bind_unlink);
  umask(omask);
  if (sock < 0)
    return 0;

  debug("Local forwarding listening on path %s.", fwd->listen_path);

  /* Allocate a channel number for the socket. */
  c = channel_new(ssh, "unix-listener", type, sock, sock, -1,
      CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
      0, "unix listener", 1);
  c->path = xstrdup(path);
  c->host_port = port;
  c->listening_port = PORT_STREAMLOCAL;
  c->listening_addr = xstrdup(fwd->listen_path);
  return 1;
}

static int
channel_cancel_rport_listener_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
  u_int i;
  int found = 0;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    Channel *c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
      continue;
    if (strcmp(c->path, host) == 0 && c->listening_port == port) {
      debug2_f("close channel %d", i);
      channel_free(ssh, c);
      found = 1;
    }
  }

  return found;
}

static int
channel_cancel_rport_listener_streamlocal(struct ssh *ssh, const char *path)
{
  u_int i;
  int found = 0;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    Channel *c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_RUNIX_LISTENER)
      continue;
    if (c->path == NULL)
      continue;
    if (strcmp(c->path, path) == 0) {
      debug2_f("close channel %d", i);
      channel_free(ssh, c);
      found = 1;
    }
  }

  return found;
}

int
channel_cancel_rport_listener(struct ssh *ssh, struct Forward *fwd)
{
  if (fwd->listen_path != NULL) {
    return channel_cancel_rport_listener_streamlocal(ssh,
        fwd->listen_path);
  } else {
    return channel_cancel_rport_listener_tcpip(ssh,
        fwd->listen_host, fwd->listen_port);
  }
}

static int
channel_cancel_lport_listener_tcpip(struct ssh *ssh,
    const char *lhost, u_short lport, int cport,
    struct ForwardOptions *fwd_opts)
{
  u_int i;
  int found = 0;
  const char *addr = channel_fwd_bind_addr(ssh, lhost, NULL, 1, fwd_opts);

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    Channel *c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_PORT_LISTENER)
      continue;
    if (c->listening_port != lport)
      continue;
    if (cport == CHANNEL_CANCEL_PORT_STATIC) {
      /* skip dynamic forwardings */
      if (c->host_port == 0)
        continue;
    } else {
      if (c->host_port != cport)
        continue;
    }
    if ((c->listening_addr == NULL && addr != NULL) ||
        (c->listening_addr != NULL && addr == NULL))
      continue;
    if (addr == NULL || strcmp(c->listening_addr, addr) == 0) {
      debug2_f("close channel %d", i);
      channel_free(ssh, c);
      found = 1;
    }
  }

  return found;
}

static int
channel_cancel_lport_listener_streamlocal(struct ssh *ssh, const char *path)
{
  u_int i;
  int found = 0;

  if (path == NULL) {
    error_f("no path specified.");
    return 0;
  }

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    Channel *c = ssh->chanctxt->channels[i];
    if (c == NULL || c->type != SSH_CHANNEL_UNIX_LISTENER)
      continue;
    if (c->listening_addr == NULL)
      continue;
    if (strcmp(c->listening_addr, path) == 0) {
      debug2_f("close channel %d", i);
      channel_free(ssh, c);
      found = 1;
    }
  }

  return found;
}

int
channel_cancel_lport_listener(struct ssh *ssh,
    struct Forward *fwd, int cport, struct ForwardOptions *fwd_opts)
{
  if (fwd->listen_path != NULL) {
    return channel_cancel_lport_listener_streamlocal(ssh,
        fwd->listen_path);
  } else {
    return channel_cancel_lport_listener_tcpip(ssh,
        fwd->listen_host, fwd->listen_port, cport, fwd_opts);
  }
}

/* protocol local port fwd, used by ssh */
int
channel_setup_local_fwd_listener(struct ssh *ssh,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
  if (fwd->listen_path != NULL) {
    return channel_setup_fwd_listener_streamlocal(ssh,
        SSH_CHANNEL_UNIX_LISTENER, fwd, fwd_opts);
  } else {
    return channel_setup_fwd_listener_tcpip(ssh,
        SSH_CHANNEL_PORT_LISTENER, fwd, NULL, fwd_opts);
  }
}

/* Matches a remote forwarding permission against a requested forwarding */
static int
remote_open_match(struct permission *allowed_open, struct Forward *fwd)
{
  int ret;
  char *lhost;

  /* XXX add ACLs for streamlocal */
  if (fwd->listen_path != NULL)
    return 1;

  if (fwd->listen_host == NULL || allowed_open->listen_host == NULL)
    return 0;

  if (allowed_open->listen_port != FWD_PERMIT_ANY_PORT &&
      allowed_open->listen_port != fwd->listen_port)
    return 0;

  /* Match hostnames case-insensitively */
  lhost = xstrdup(fwd->listen_host);
  lowercase(lhost);
  ret = match_pattern(lhost, allowed_open->listen_host);
  free(lhost);

  return ret;
}

/* Checks whether a requested remote forwarding is permitted */
static int
check_rfwd_permission(struct ssh *ssh, struct Forward *fwd)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->remote_perms;
  u_int i, permit, permit_adm = 1;
  struct permission *perm;

#ifdef SKIP_PRIVDROP
  if (fwd->listen_path != NULL)
    return 0;
  if (fwd->listen_port != 0 && fwd->listen_port < 1024)
    return 0;
#endif

  /* XXX apply GatewayPorts override before checking? */

  permit = pset->all_permitted;
  if (!permit) {
    for (i = 0; i < pset->num_permitted_user; i++) {
      perm = &pset->permitted_user[i];
      if (remote_open_match(perm, fwd)) {
        permit = 1;
        break;
      }
    }
  }

  if (pset->num_permitted_admin > 0) {
    permit_adm = 0;
    for (i = 0; i < pset->num_permitted_admin; i++) {
      perm = &pset->permitted_admin[i];
      if (remote_open_match(perm, fwd)) {
        permit_adm = 1;
        break;
      }
    }
  }

  return permit && permit_adm;
}

/* protocol v2 remote port fwd, used by sshd */
int
channel_setup_remote_fwd_listener(struct ssh *ssh, struct Forward *fwd,
    int *allocated_listen_port, struct ForwardOptions *fwd_opts)
{
  if (!check_rfwd_permission(ssh, fwd)) {
    ssh_packet_send_debug(ssh, "port forwarding refused");
    if (fwd->listen_path != NULL)
      /* XXX always allowed, see remote_open_match() */
      logit("Received request from %.100s port %d to "
          "remote forward to path \"%.100s\", "
          "but the request was denied.",
          ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
          fwd->listen_path);
    else if(fwd->listen_host != NULL)
      logit("Received request from %.100s port %d to "
          "remote forward to host %.100s port %d, "
          "but the request was denied.",
          ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
          fwd->listen_host, fwd->listen_port );
    else
      logit("Received request from %.100s port %d to remote "
          "forward, but the request was denied.",
          ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
    return 0;
  }
  if (fwd->listen_path != NULL) {
    return channel_setup_fwd_listener_streamlocal(ssh,
        SSH_CHANNEL_RUNIX_LISTENER, fwd, fwd_opts);
  } else {
    return channel_setup_fwd_listener_tcpip(ssh,
        SSH_CHANNEL_RPORT_LISTENER, fwd, allocated_listen_port,
        fwd_opts);
  }
}

/*
 * Translate the requested rfwd listen host to something usable for
 * this server.
 */
static const char *
channel_rfwd_bind_host(const char *listen_host)
{
  if (listen_host == NULL) {
    return "localhost";
  } else if (*listen_host == '\0' || strcmp(listen_host, "*") == 0) {
    return "";
  } else
    return listen_host;
}

/*
 * Initiate forwarding of connections to port "port" on remote host through
 * the secure channel to host:port from local side.
 * Returns handle (index) for updating the dynamic listen port with
 * channel_update_permission().
 */
int
channel_request_remote_forwarding(struct ssh *ssh, struct Forward *fwd)
{
  int r, success = 0, idx = -1;
  const char *host_to_connect, *listen_host, *listen_path;
  int port_to_connect, listen_port;

  /* Send the forward request to the remote side. */
  if (fwd->listen_path != NULL) {
    if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
        (r = sshpkt_put_cstring(ssh,
        "streamlocal-forward@openssh.com")) != 0 ||
        (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
        (r = sshpkt_put_cstring(ssh, fwd->listen_path)) != 0 ||
        (r = sshpkt_send(ssh)) != 0 ||
        (r = ssh_packet_write_wait(ssh)) != 0)
      fatal_fr(r, "request streamlocal");
  } else {
    if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
        (r = sshpkt_put_cstring(ssh, "tcpip-forward")) != 0 ||
        (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
        (r = sshpkt_put_cstring(ssh,
        channel_rfwd_bind_host(fwd->listen_host))) != 0 ||
        (r = sshpkt_put_u32(ssh, fwd->listen_port)) != 0 ||
        (r = sshpkt_send(ssh)) != 0 ||
        (r = ssh_packet_write_wait(ssh)) != 0)
      fatal_fr(r, "request tcpip-forward");
  }
  /* Assume that server accepts the request */
  success = 1;
  if (success) {
    /* Record that connection to this host/port is permitted. */
    host_to_connect = listen_host = listen_path = NULL;
    port_to_connect = listen_port = 0;
    if (fwd->connect_path != NULL) {
      host_to_connect = fwd->connect_path;
      port_to_connect = PORT_STREAMLOCAL;
    } else {
      host_to_connect = fwd->connect_host;
      port_to_connect = fwd->connect_port;
    }
    if (fwd->listen_path != NULL) {
      listen_path = fwd->listen_path;
      listen_port = PORT_STREAMLOCAL;
    } else {
      listen_host = fwd->listen_host;
      listen_port = fwd->listen_port;
    }
    idx = permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL,
        host_to_connect, port_to_connect,
        listen_host, listen_path, listen_port, NULL);
  }
  return idx;
}

static int
open_match(struct permission *allowed_open, const char *requestedhost,
    int requestedport)
{
  if (allowed_open->host_to_connect == NULL)
    return 0;
  if (allowed_open->port_to_connect != FWD_PERMIT_ANY_PORT &&
      allowed_open->port_to_connect != requestedport)
    return 0;
  if (strcmp(allowed_open->host_to_connect, FWD_PERMIT_ANY_HOST) != 0 &&
      strcmp(allowed_open->host_to_connect, requestedhost) != 0)
    return 0;
  return 1;
}

/*
 * Note that in the listen host/port case
 * we don't support FWD_PERMIT_ANY_PORT and
 * need to translate between the configured-host (listen_host)
 * and what we've sent to the remote server (channel_rfwd_bind_host)
 */
static int
open_listen_match_tcpip(struct permission *allowed_open,
    const char *requestedhost, u_short requestedport, int translate)
{
  const char *allowed_host;

  if (allowed_open->host_to_connect == NULL)
    return 0;
  if (allowed_open->listen_port != requestedport)
    return 0;
  if (!translate && allowed_open->listen_host == NULL &&
      requestedhost == NULL)
    return 1;
  allowed_host = translate ?
      channel_rfwd_bind_host(allowed_open->listen_host) :
      allowed_open->listen_host;
  if (allowed_host == NULL || requestedhost == NULL ||
      strcmp(allowed_host, requestedhost) != 0)
    return 0;
  return 1;
}

static int
open_listen_match_streamlocal(struct permission *allowed_open,
    const char *requestedpath)
{
  if (allowed_open->host_to_connect == NULL)
    return 0;
  if (allowed_open->listen_port != PORT_STREAMLOCAL)
    return 0;
  if (allowed_open->listen_path == NULL ||
      strcmp(allowed_open->listen_path, requestedpath) != 0)
    return 0;
  return 1;
}

/*
 * Request cancellation of remote forwarding of connection host:port from
 * local side.
 */
static int
channel_request_rforward_cancel_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  int r;
  u_int i;
  struct permission *perm = NULL;

  for (i = 0; i < pset->num_permitted_user; i++) {
    perm = &pset->permitted_user[i];
    if (open_listen_match_tcpip(perm, host, port, 0))
      break;
    perm = NULL;
  }
  if (perm == NULL) {
    debug_f("requested forward not found");
    return -1;
  }
  if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
      (r = sshpkt_put_cstring(ssh, "cancel-tcpip-forward")) != 0 ||
      (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
      (r = sshpkt_put_cstring(ssh, channel_rfwd_bind_host(host))) != 0 ||
      (r = sshpkt_put_u32(ssh, port)) != 0 ||
      (r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "send cancel");

  fwd_perm_clear(perm); /* unregister */

  return 0;
}

/*
 * Request cancellation of remote forwarding of Unix domain socket
 * path from local side.
 */
static int
channel_request_rforward_cancel_streamlocal(struct ssh *ssh, const char *path)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  int r;
  u_int i;
  struct permission *perm = NULL;

  for (i = 0; i < pset->num_permitted_user; i++) {
    perm = &pset->permitted_user[i];
    if (open_listen_match_streamlocal(perm, path))
      break;
    perm = NULL;
  }
  if (perm == NULL) {
    debug_f("requested forward not found");
    return -1;
  }
  if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
      (r = sshpkt_put_cstring(ssh,
      "cancel-streamlocal-forward@openssh.com")) != 0 ||
      (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
      (r = sshpkt_put_cstring(ssh, path)) != 0 ||
      (r = sshpkt_send(ssh)) != 0)
    fatal_fr(r, "send cancel");

  fwd_perm_clear(perm); /* unregister */

  return 0;
}

/*
 * Request cancellation of remote forwarding of a connection from local side.
 */
int
channel_request_rforward_cancel(struct ssh *ssh, struct Forward *fwd)
{
  if (fwd->listen_path != NULL) {
    return channel_request_rforward_cancel_streamlocal(ssh,
        fwd->listen_path);
  } else {
    return channel_request_rforward_cancel_tcpip(ssh,
        fwd->listen_host,
        fwd->listen_port ? fwd->listen_port : fwd->allocated_port);
  }
}

/*
 * Permits opening to any host/port if permitted_user[] is empty.  This is
 * usually called by the server, because the user could connect to any port
 * anyway, and the server has no way to know but to trust the client anyway.
 */
void
channel_permit_all(struct ssh *ssh, int where)
{
  struct permission_set *pset = permission_set_get(ssh, where);

  if (pset->num_permitted_user == 0)
    pset->all_permitted = 1;
}

/*
 * Permit the specified host/port for forwarding.
 */
void
channel_add_permission(struct ssh *ssh, int who, int where,
    char *host, int port)
{
  int local = where == FORWARD_LOCAL;
  struct permission_set *pset = permission_set_get(ssh, where);

  debug("allow %s forwarding to host %s port %d",
      fwd_ident(who, where), host, port);
  /*
   * Remote forwards set listen_host/port, local forwards set
   * host/port_to_connect.
   */
  permission_set_add(ssh, who, where,
      local ? host : NULL, local ? port : 0,
      local ? NULL : host, NULL, local ? 0 : port, NULL);
  pset->all_permitted = 0;
}

/*
 * Administratively disable forwarding.
 */
void
channel_disable_admin(struct ssh *ssh, int where)
{
  channel_clear_permission(ssh, FORWARD_ADM, where);
  permission_set_add(ssh, FORWARD_ADM, where,
      NULL, 0, NULL, NULL, 0, NULL);
}

/*
 * Clear a list of permitted opens.
 */
void
channel_clear_permission(struct ssh *ssh, int who, int where)
{
  struct permission **permp;
  u_int i, *npermp;

  permission_set_get_array(ssh, who, where, &permp, &npermp);
  for (i = 0; i < *npermp; i++)
    fwd_perm_clear((*permp) + i);
  free(*permp);
  *permp = NULL;
  *npermp = 0;
}

/*
 * Update the listen port for a dynamic remote forward, after
 * the actual 'newport' has been allocated. If 'newport' < 0 is
 * passed then they entry will be invalidated.
 */
void
channel_update_permission(struct ssh *ssh, int idx, int newport)
{
  struct permission_set *pset = &ssh->chanctxt->local_perms;

  if (idx < 0 || (u_int)idx >= pset->num_permitted_user) {
    debug_f("index out of range: %d num_permitted_user %d",
        idx, pset->num_permitted_user);
    return;
  }
  debug("%s allowed port %d for forwarding to host %s port %d",
      newport > 0 ? "Updating" : "Removing",
      newport,
      pset->permitted_user[idx].host_to_connect,
      pset->permitted_user[idx].port_to_connect);
  if (newport <= 0)
    fwd_perm_clear(&pset->permitted_user[idx]);
  else {
    pset->permitted_user[idx].listen_port =
        (ssh->compat & SSH_BUG_DYNAMIC_RPORT) ? 0 : newport;
  }
}

/* Try to start non-blocking connect to next host in cctx list */
static int
connect_next(struct ssh *ssh, struct channel_connect *cctx)
{
  int sock, sock_is_network, saved_errno;
  struct sockaddr_un *sunaddr;
  char ntop[NI_MAXHOST];
  char strport[MAXIMUM(NI_MAXSERV, sizeof(sunaddr->sun_path))];

  for (; cctx->ai; cctx->ai = cctx->ai->ai_next) {
    sock_is_network = 0;
    switch (cctx->ai->ai_family) {
    case AF_UNIX:
      /* unix:pathname instead of host:port */
      sunaddr = (struct sockaddr_un *)cctx->ai->ai_addr;
      strlcpy(ntop, "unix", sizeof(ntop));
      strlcpy(strport, sunaddr->sun_path, sizeof(strport));
      break;
    case AF_INET:
    case AF_INET6:
      if (getnameinfo(cctx->ai->ai_addr, cctx->ai->ai_addrlen,
          ntop, sizeof(ntop), strport, sizeof(strport),
          NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
        error_f("getnameinfo failed");
        continue;
      }
      sock_is_network = 1;
      break;
    default:
      continue;
    }
    debug_f("start for host %.100s ([%.100s]:%s)",
        cctx->host, ntop, strport);
    if ((sock = socket(cctx->ai->ai_family, cctx->ai->ai_socktype,
        cctx->ai->ai_protocol)) == -1) {
      if (cctx->ai->ai_next == NULL)
        error("socket: %.100s", strerror(errno));
      else
        verbose("socket: %.100s", strerror(errno));
      continue;
    }
    if (set_nonblock(sock) == -1)
      fatal_f("set_nonblock(%d)", sock);
    if (sock_is_network && ssh->chanctxt->want_tcp_keepalive)
      set_keepalive(sock); /* logs errors */
    if (connect(sock, cctx->ai->ai_addr,
        cctx->ai->ai_addrlen) == -1 && errno != EINPROGRESS) {
      debug_f("host %.100s ([%.100s]:%s): %.100s",
          cctx->host, ntop, strport, strerror(errno));
      saved_errno = errno;
      close(sock);
      errno = saved_errno;
      continue; /* fail -- try next */
    }
    if (cctx->ai->ai_family != AF_UNIX)
      set_nodelay(sock);
    debug_f("connect host %.100s ([%.100s]:%s) in progress, fd=%d",
        cctx->host, ntop, strport, sock);
    cctx->ai = cctx->ai->ai_next;
    return sock;
  }
  return -1;
}

/*
 * Return connecting socket to remote host:port or local socket path,
 * passing back the failure reason if appropriate.
 */
static int
connect_to_helper(struct ssh *ssh, const char *name, int port, int socktype,
    char *ctype, char *rname, struct channel_connect *cctx,
    int *reason, const char **errmsg)
{
  struct addrinfo hints;
  int gaierr;
  int sock = -1;
  char strport[NI_MAXSERV];

  if (port == PORT_STREAMLOCAL) {
    struct sockaddr_un *sunaddr;
    struct addrinfo *ai;

    if (strlen(name) > sizeof(sunaddr->sun_path)) {
      error("%.100s: %.100s", name, strerror(ENAMETOOLONG));
      return -1;
    }

    /*
     * Fake up a struct addrinfo for AF_UNIX connections.
     * free_connect_ctx() must check ai_family
     * and use free() not freeaddrinfo() for AF_UNIX.
     */
    ai = xcalloc(1, sizeof(*ai) + sizeof(*sunaddr));
    ai->ai_addr = (struct sockaddr *)(ai + 1);
    ai->ai_addrlen = sizeof(*sunaddr);
    ai->ai_family = AF_UNIX;
    ai->ai_socktype = socktype;
    ai->ai_protocol = PF_UNSPEC;
    sunaddr = (struct sockaddr_un *)ai->ai_addr;
    sunaddr->sun_family = AF_UNIX;
    strlcpy(sunaddr->sun_path, name, sizeof(sunaddr->sun_path));
    cctx->aitop = ai;
  } else {
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = ssh->chanctxt->IPv4or6;
    hints.ai_socktype = socktype;
    snprintf(strport, sizeof strport, "%d", port);
    if ((gaierr = getaddrinfo(name, strport, &hints, &cctx->aitop))
        != 0) {
      if (errmsg != NULL)
        *errmsg = ssh_gai_strerror(gaierr);
      if (reason != NULL)
        *reason = SSH2_OPEN_CONNECT_FAILED;
      error("connect_to %.100s: unknown host (%s)", name,
          ssh_gai_strerror(gaierr));
      return -1;
    }
  }

  cctx->host = xstrdup(name);
  cctx->port = port;
  cctx->ai = cctx->aitop;

  if ((sock = connect_next(ssh, cctx)) == -1) {
    error("connect to %.100s port %d failed: %s",
        name, port, strerror(errno));
    return -1;
  }

  return sock;
}

/* Return CONNECTING channel to remote host:port or local socket path */
static Channel *
connect_to(struct ssh *ssh, const char *host, int port,
    char *ctype, char *rname)
{
  struct channel_connect cctx;
  Channel *c;
  int sock;

  memset(&cctx, 0, sizeof(cctx));
  sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
      &cctx, NULL, NULL);
  if (sock == -1) {
    free_connect_ctx(&cctx);
    return NULL;
  }
  c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
      CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  c->host_port = port;
  c->path = xstrdup(host);
  c->connect_ctx = xmalloc(sizeof(cctx));
  memcpy(c->connect_ctx, &cctx, sizeof(cctx));

  return c;
}

/*
 * returns either the newly connected channel or the downstream channel
 * that needs to deal with this connection.
 */
Channel *
channel_connect_by_listen_address(struct ssh *ssh, const char *listen_host,
    u_short listen_port, char *ctype, char *rname)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  u_int i;
  struct permission *perm;

  for (i = 0; i < pset->num_permitted_user; i++) {
    perm = &pset->permitted_user[i];
    if (open_listen_match_tcpip(perm,
        listen_host, listen_port, 1)) {
      if (perm->downstream)
        return perm->downstream;
      if (perm->port_to_connect == 0)
        return rdynamic_connect_prepare(ssh,
            ctype, rname);
      return connect_to(ssh,
          perm->host_to_connect, perm->port_to_connect,
          ctype, rname);
    }
  }
  error("WARNING: Server requests forwarding for unknown listen_port %d",
      listen_port);
  return NULL;
}

Channel *
channel_connect_by_listen_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  u_int i;
  struct permission *perm;

  for (i = 0; i < pset->num_permitted_user; i++) {
    perm = &pset->permitted_user[i];
    if (open_listen_match_streamlocal(perm, path)) {
      return connect_to(ssh,
          perm->host_to_connect, perm->port_to_connect,
          ctype, rname);
    }
  }
  error("WARNING: Server requests forwarding for unknown path %.100s",
      path);
  return NULL;
}

/* Check if connecting to that port is permitted and connect. */
Channel *
channel_connect_to_port(struct ssh *ssh, const char *host, u_short port,
    char *ctype, char *rname, int *reason, const char **errmsg)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  struct channel_connect cctx;
  Channel *c;
  u_int i, permit, permit_adm = 1;
  int sock;
  struct permission *perm;

  permit = pset->all_permitted;
  if (!permit) {
    for (i = 0; i < pset->num_permitted_user; i++) {
      perm = &pset->permitted_user[i];
      if (open_match(perm, host, port)) {
        permit = 1;
        break;
      }
    }
  }

  if (pset->num_permitted_admin > 0) {
    permit_adm = 0;
    for (i = 0; i < pset->num_permitted_admin; i++) {
      perm = &pset->permitted_admin[i];
      if (open_match(perm, host, port)) {
        permit_adm = 1;
        break;
      }
    }
  }

  if (!permit || !permit_adm) {
    logit("Received request from %.100s port %d to connect to "
        "host %.100s port %d, but the request was denied.",
        ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), host, port);
    if (reason != NULL)
      *reason = SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED;
    return NULL;
  }

  memset(&cctx, 0, sizeof(cctx));
  sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
      &cctx, reason, errmsg);
  if (sock == -1) {
    free_connect_ctx(&cctx);
    return NULL;
  }

  c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
      CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  c->host_port = port;
  c->path = xstrdup(host);
  c->connect_ctx = xmalloc(sizeof(cctx));
  memcpy(c->connect_ctx, &cctx, sizeof(cctx));

  return c;
}

/* Check if connecting to that path is permitted and connect. */
Channel *
channel_connect_to_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  u_int i, permit, permit_adm = 1;
  struct permission *perm;

  permit = pset->all_permitted;
  if (!permit) {
    for (i = 0; i < pset->num_permitted_user; i++) {
      perm = &pset->permitted_user[i];
      if (open_match(perm, path, PORT_STREAMLOCAL)) {
        permit = 1;
        break;
      }
    }
  }

  if (pset->num_permitted_admin > 0) {
    permit_adm = 0;
    for (i = 0; i < pset->num_permitted_admin; i++) {
      perm = &pset->permitted_admin[i];
      if (open_match(perm, path, PORT_STREAMLOCAL)) {
        permit_adm = 1;
        break;
      }
    }
  }

  if (!permit || !permit_adm) {
    logit("Received request to connect to path %.100s, "
        "but the request was denied.", path);
    return NULL;
  }
  return connect_to(ssh, path, PORT_STREAMLOCAL, ctype, rname);
}

void
channel_send_window_changes(struct ssh *ssh)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct winsize ws;
  int r;
  u_int i;

  for (i = 0; i < sc->channels_alloc; i++) {
    if (sc->channels[i] == NULL || !sc->channels[i]->client_tty ||
        sc->channels[i]->type != SSH_CHANNEL_OPEN)
      continue;
    if (ioctl(sc->channels[i]->rfd, TIOCGWINSZ, &ws) == -1)
      continue;
    channel_request_start(ssh, i, "window-change", 0);
    if ((r = sshpkt_put_u32(ssh, (u_int)ws.ws_col)) != 0 ||
        (r = sshpkt_put_u32(ssh, (u_int)ws.ws_row)) != 0 ||
        (r = sshpkt_put_u32(ssh, (u_int)ws.ws_xpixel)) != 0 ||
        (r = sshpkt_put_u32(ssh, (u_int)ws.ws_ypixel)) != 0 ||
        (r = sshpkt_send(ssh)) != 0)
      fatal_fr(r, "channel %u; send window-change", i);
  }
}

/* Return RDYNAMIC_OPEN channel: channel allows SOCKS, but is not connected */
static Channel *
rdynamic_connect_prepare(struct ssh *ssh, char *ctype, char *rname)
{
  Channel *c;
  int r;

  c = channel_new(ssh, ctype, SSH_CHANNEL_RDYNAMIC_OPEN, -1, -1, -1,
      CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
  c->host_port = 0;
  c->path = NULL;

  /*
   * We need to open the channel before we have a FD,
   * so that we can get SOCKS header from peer.
   */
  if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
      (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0)
    fatal_fr(r, "channel %i; confirm", c->self);
  return c;
}

/* Return CONNECTING socket to remote host:port or local socket path */
static int
rdynamic_connect_finish(struct ssh *ssh, Channel *c)
{
  struct ssh_channels *sc = ssh->chanctxt;
  struct permission_set *pset = &sc->local_perms;
  struct permission *perm;
  struct channel_connect cctx;
  u_int i, permit_adm = 1;
  int sock;

  if (pset->num_permitted_admin > 0) {
    permit_adm = 0;
    for (i = 0; i < pset->num_permitted_admin; i++) {
      perm = &pset->permitted_admin[i];
      if (open_match(perm, c->path, c->host_port)) {
        permit_adm = 1;
        break;
      }
    }
  }
  if (!permit_adm) {
    debug_f("requested forward not permitted");
    return -1;
  }

  memset(&cctx, 0, sizeof(cctx));
  sock = connect_to_helper(ssh, c->path, c->host_port, SOCK_STREAM, NULL,
      NULL, &cctx, NULL, NULL);
  if (sock == -1)
    free_connect_ctx(&cctx);
  else {
    /* similar to SSH_CHANNEL_CONNECTING but we've already sent the open */
    c->type = SSH_CHANNEL_RDYNAMIC_FINISH;
    c->connect_ctx = xmalloc(sizeof(cctx));
    memcpy(c->connect_ctx, &cctx, sizeof(cctx));
    channel_register_fds(ssh, c, sock, sock, -1, 0, 1, 0);
  }
  return sock;
}

/* -- X11 forwarding */

/*
 * Creates an internet domain socket for listening for X11 connections.
 * Returns 0 and a suitable display number for the DISPLAY variable
 * stored in display_numberp , or -1 if an error occurs.
 */
int
x11_create_display_inet(struct ssh *ssh, int x11_display_offset,
    int x11_use_localhost, int single_connection,
    u_int *display_numberp, int **chanids)
{
  Channel *nc = NULL;
  int display_number, sock, port;
  struct addrinfo hints, *ai, *aitop;
  char strport[NI_MAXSERV];
  int gaierr, n, num_socks = 0, socks[NUM_SOCKS];

  if (chanids == NULL || x11_display_offset < 0 ||
      x11_display_offset > UINT16_MAX - X11_BASE_PORT - MAX_DISPLAYS)
    return -1;

  for (display_number = x11_display_offset;
      display_number < x11_display_offset + MAX_DISPLAYS;
      display_number++) {
    port = X11_BASE_PORT + display_number;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = ssh->chanctxt->IPv4or6;
    hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
    hints.ai_socktype = SOCK_STREAM;
    snprintf(strport, sizeof strport, "%d", port);
    if ((gaierr = getaddrinfo(NULL, strport,
        &hints, &aitop)) != 0) {
      error("getaddrinfo: %.100s", ssh_gai_strerror(gaierr));
      return -1;
    }
    for (ai = aitop; ai; ai = ai->ai_next) {
      if (ai->ai_family != AF_INET &&
          ai->ai_family != AF_INET6)
        continue;
      sock = socket(ai->ai_family, ai->ai_socktype,
          ai->ai_protocol);
      if (sock == -1) {
        if ((errno != EINVAL) && (errno != EAFNOSUPPORT)
#ifdef EPFNOSUPPORT
            && (errno != EPFNOSUPPORT)
#endif 
            ) {
          error("socket: %.100s", strerror(errno));
          freeaddrinfo(aitop);
          return -1;
        } else {
          debug("x11_create_display_inet: Socket family %d not supported",
             ai->ai_family);
          continue;
        }
      }
      if (ai->ai_family == AF_INET6)
        sock_set_v6only(sock);
      if (x11_use_localhost)
        set_reuseaddr(sock);
      if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
        debug2_f("bind port %d: %.100s", port,
            strerror(errno));
        close(sock);
        for (n = 0; n < num_socks; n++)
          close(socks[n]);
        num_socks = 0;
        break;
      }
      socks[num_socks++] = sock;
      if (num_socks == NUM_SOCKS)
        break;
    }
    freeaddrinfo(aitop);
    if (num_socks > 0)
      break;
  }
  if (display_number >= x11_display_offset + MAX_DISPLAYS) {
    error("Failed to allocate internet-domain X11 display socket.");
    return -1;
  }
  /* Start listening for connections on the socket. */
  for (n = 0; n < num_socks; n++) {
    sock = socks[n];
    if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
      error("listen: %.100s", strerror(errno));
      close(sock);
      return -1;
    }
  }

  /* Allocate a channel for each socket. */
  *chanids = xcalloc(num_socks + 1, sizeof(**chanids));
  for (n = 0; n < num_socks; n++) {
    sock = socks[n];
    nc = channel_new(ssh, "x11-listener",
        SSH_CHANNEL_X11_LISTENER, sock, sock, -1,
        CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
        0, "X11 inet listener", 1);
    nc->single_connection = single_connection;
    (*chanids)[n] = nc->self;
  }
  (*chanids)[n] = -1;

  /* Return the display number for the DISPLAY environment variable. */
  *display_numberp = display_number;
  return 0;
}

static int
connect_local_xsocket_path(const char *pathname)
{
  int sock;
  struct sockaddr_un addr;

  sock = socket(AF_UNIX, SOCK_STREAM, 0);
  if (sock == -1) {
    error("socket: %.100s", strerror(errno));
    return -1;
  }
  memset(&addr, 0, sizeof(addr));
  addr.sun_family = AF_UNIX;
  strlcpy(addr.sun_path, pathname, sizeof addr.sun_path);
  if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == 0)
    return sock;
  close(sock);
  error("connect %.100s: %.100s", addr.sun_path, strerror(errno));
  return -1;
}

static int
connect_local_xsocket(u_int dnr)
{
  char buf[1024];
  snprintf(buf, sizeof buf, _PATH_UNIX_X, dnr);
  return connect_local_xsocket_path(buf);
}

#ifdef __APPLE__
static int
is_path_to_xsocket(const char *display, char *path, size_t pathlen)
{
  struct stat sbuf;

  if (strlcpy(path, display, pathlen) >= pathlen) {
    error_f("display path too long");
    return 0;
  }
  if (display[0] != '/')
    return 0;
  if (stat(path, &sbuf) == 0) {
    return 1;
  } else {
    char *dot = strrchr(path, '.');
    if (dot != NULL) {
      *dot = '\0';
      if (stat(path, &sbuf) == 0) {
        return 1;
      }
    }
  }
  return 0;
}
#endif

int
x11_connect_display(struct ssh *ssh)
{
  u_int display_number;
  const char *display;
  char buf[1024], *cp;
  struct addrinfo hints, *ai, *aitop;
  char strport[NI_MAXSERV];
  int gaierr, sock = 0;

  /* Try to open a socket for the local X server. */
  display = getenv("DISPLAY");
  if (!display) {
    error("DISPLAY not set.");
    return -1;
  }
  /*
   * Now we decode the value of the DISPLAY variable and make a
   * connection to the real X server.
   */

#ifdef __APPLE__
  /* Check if display is a path to a socket (as set by launchd). */
  {
    char path[PATH_MAX];

    if (is_path_to_xsocket(display, path, sizeof(path))) {
      debug("x11_connect_display: $DISPLAY is launchd");

      /* Create a socket. */
      sock = connect_local_xsocket_path(path);
      if (sock < 0)
        return -1;

      /* OK, we now have a connection to the display. */
      return sock;
    }
  }
#endif
  /*
   * Check if it is a unix domain socket.  Unix domain displays are in
   * one of the following formats: unix:d[.s], :d[.s], ::d[.s]
   */
  if (strncmp(display, "unix:", 5) == 0 ||
      display[0] == ':') {
    /* Connect to the unix domain socket. */
    if (sscanf(strrchr(display, ':') + 1, "%u",
        &display_number) != 1) {
      error("Could not parse display number from DISPLAY: "
          "%.100s", display);
      return -1;
    }
    /* Create a socket. */
    sock = connect_local_xsocket(display_number);
    if (sock < 0)
      return -1;

    /* OK, we now have a connection to the display. */
    return sock;
  }
  /*
   * Connect to an inet socket.  The DISPLAY value is supposedly
   * hostname:d[.s], where hostname may also be numeric IP address.
   */
  strlcpy(buf, display, sizeof(buf));
  cp = strchr(buf, ':');
  if (!cp) {
    error("Could not find ':' in DISPLAY: %.100s", display);
    return -1;
  }
  *cp = 0;
  /*
   * buf now contains the host name.  But first we parse the
   * display number.
   */
  if (sscanf(cp + 1, "%u", &display_number) != 1 ||
      display_number > UINT16_MAX - X11_BASE_PORT) {
    error("Could not parse display number from DISPLAY: %.100s",
        display);
    return -1;
  }

  /* Look up the host address */
  memset(&hints, 0, sizeof(hints));
  hints.ai_family = ssh->chanctxt->IPv4or6;
  hints.ai_socktype = SOCK_STREAM;
  snprintf(strport, sizeof strport, "%u", X11_BASE_PORT + display_number);
  if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
    error("%.100s: unknown host. (%s)", buf,
    ssh_gai_strerror(gaierr));
    return -1;
  }
  for (ai = aitop; ai; ai = ai->ai_next) {
    /* Create a socket. */
    sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
    if (sock == -1) {
      debug2("socket: %.100s", strerror(errno));
      continue;
    }
    /* Connect it to the display. */
    if (connect(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
      debug2("connect %.100s port %u: %.100s", buf,
          X11_BASE_PORT + display_number, strerror(errno));
      close(sock);
      continue;
    }
    /* Success */
    break;
  }
  freeaddrinfo(aitop);
  if (!ai) {
    error("connect %.100s port %u: %.100s", buf,
        X11_BASE_PORT + display_number, strerror(errno));
    return -1;
  }
  set_nodelay(sock);
  return sock;
}

/*
 * Requests forwarding of X11 connections, generates fake authentication
 * data, and enables authentication spoofing.
 * This should be called in the client only.
 */
void
x11_request_forwarding_with_spoofing(struct ssh *ssh, int client_session_id,
    const char *disp, const char *proto, const char *data, int want_reply)
{
  struct ssh_channels *sc = ssh->chanctxt;
  u_int data_len = (u_int) strlen(data) / 2;
  u_int i, value;
  const char *cp;
  char *new_data;
  int r, screen_number;

  if (sc->x11_saved_display == NULL)
    sc->x11_saved_display = xstrdup(disp);
  else if (strcmp(disp, sc->x11_saved_display) != 0) {
    error("x11_request_forwarding_with_spoofing: different "
        "$DISPLAY already forwarded");
    return;
  }

  cp = strchr(disp, ':');
  if (cp)
    cp = strchr(cp, '.');
  if (cp)
    screen_number = (u_int)strtonum(cp + 1, 0, 400, NULL);
  else
    screen_number = 0;

  if (sc->x11_saved_proto == NULL) {
    /* Save protocol name. */
    sc->x11_saved_proto = xstrdup(proto);

    /* Extract real authentication data. */
    sc->x11_saved_data = xmalloc(data_len);
    for (i = 0; i < data_len; i++) {
      if (sscanf(data + 2 * i, "%2x", &value) != 1) {
        fatal("x11_request_forwarding: bad "
            "authentication data: %.100s", data);
      }
      sc->x11_saved_data[i] = value;
    }
    sc->x11_saved_data_len = data_len;

    /* Generate fake data of the same length. */
    sc->x11_fake_data = xmalloc(data_len);
    arc4random_buf(sc->x11_fake_data, data_len);
    sc->x11_fake_data_len = data_len;
  }

  /* Convert the fake data into hex. */
  new_data = tohex(sc->x11_fake_data, data_len);

  /* Send the request packet. */
  channel_request_start(ssh, client_session_id, "x11-req", want_reply);
  if ((r = sshpkt_put_u8(ssh, 0)) != 0 || /* bool: single connection */
      (r = sshpkt_put_cstring(ssh, proto)) != 0 ||
      (r = sshpkt_put_cstring(ssh, new_data)) != 0 ||
      (r = sshpkt_put_u32(ssh, screen_number)) != 0 ||
      (r = sshpkt_send(ssh)) != 0 ||
      (r = ssh_packet_write_wait(ssh)) != 0)
    fatal_fr(r, "send x11-req");
  free(new_data);
}

/*
 * Returns whether an x11 channel was used recently (less than a second ago)
 */
int
x11_channel_used_recently(struct ssh *ssh) {
  u_int i;
  Channel *c;
  double lastused = 0;

  for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
    c = ssh->chanctxt->channels[i];
    if (c == NULL || c->ctype == NULL || c->lastused == 0.0 ||
        strcmp(c->ctype, "x11-connection") != 0)
      continue;
    if (c->lastused > lastused)
      lastused = c->lastused;
  }
  return lastused != 0.0 && monotime_double() <= lastused + 1.0;
}

Coverage Report

Created: 2026-10-23 07:09