/src/openssh/session.c

Source
/* $OpenBSD: session.c,v 1.351 2026/09/16 00:25:50 djm Exp $ */
/*
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 *
 * 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 by Markus Friedl.
 * Copyright (c) 2000, 2001 Markus Friedl.  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/wait.h>
#include <sys/un.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/queue.h>

#include <arpa/inet.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <netdb.h>
#include <paths.h>
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <unistd.h>
#include <limits.h>

#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "sshpty.h"
#include "packet.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "match.h"
#include "uidswap.h"
#include "channels.h"
#include "sshkey.h"
#include "cipher.h"
#include "kex.h"
#include "hostfile.h"
#include "auth.h"
#include "auth-options.h"
#include "authfd.h"
#include "pathnames.h"
#include "log.h"
#include "misc.h"
#include "servconf.h"
#include "sshlogin.h"
#include "serverloop.h"
#include "canohost.h"
#include "session.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "sftp.h"
#include "atomicio.h"

#if defined(KRB5) && defined(USE_AFS)
#include <kafs.h>
#endif

#ifdef WITH_SELINUX
#include <selinux/selinux.h>
#endif

/*
 * Hack for systems that do not support FD passing: allocate PTYs directly
 * without calling into the monitor. This requires either the post-auth
 * privsep process retain root privileges (see the comment in
 * sshd-session.c:privsep_postauth) or that PTY allocation doesn't require
 * privileges to begin with (e.g. Cygwin).
 */
#ifdef DISABLE_FD_PASSING
#define mm_pty_allocate pty_allocate
#endif

#define IS_INTERNAL_SFTP(c) \
  (!strncmp(c, INTERNAL_SFTP_NAME, sizeof(INTERNAL_SFTP_NAME) - 1) && \
   (c[sizeof(INTERNAL_SFTP_NAME) - 1] == '\0' || \
    c[sizeof(INTERNAL_SFTP_NAME) - 1] == ' ' || \
    c[sizeof(INTERNAL_SFTP_NAME) - 1] == '\t'))

/* func */

Session *session_new(void);
void  session_set_fds(struct ssh *, Session *, int, int, int, int, int);
void  session_pty_cleanup(Session *);
void  session_proctitle(Session *);
int session_setup_x11fwd(struct ssh *, Session *);
int do_exec_pty(struct ssh *, Session *, const char *);
int do_exec_no_pty(struct ssh *, Session *, const char *);
int do_exec(struct ssh *, Session *, const char *);
void  do_login(struct ssh *, Session *, const char *);
void  do_child(struct ssh *, Session *, const char *);
void  do_motd(void);
int check_quietlogin(Session *, const char *);

static void do_authenticated2(struct ssh *, Authctxt *);

static int session_pty_req(struct ssh *, Session *);

/* import */
extern ServerOptions options;
extern char *__progname;
extern int debug_flag;
extern struct sshbuf *loginmsg;
extern struct sshauthopt *auth_opts;
extern char *tun_fwd_ifnames; /* serverloop.c */

/* original command from peer. */
const char *original_command = NULL;

/* data */
static int sessions_first_unused = -1;
static int sessions_nalloc = 0;
static Session *sessions = NULL;

#define SUBSYSTEM_NONE      0
#define SUBSYSTEM_EXT     1
#define SUBSYSTEM_INT_SFTP    2
#define SUBSYSTEM_INT_SFTP_ERROR  3

#ifdef HAVE_LOGIN_CAP
login_cap_t *lc;
#endif

static int is_child = 0;
static int in_chroot = 0;

/* File containing userauth info, if ExposeAuthInfo set */
static char *auth_info_file = NULL;

/* Name and directory of socket for authentication agent forwarding. */
static char *auth_sock_name = NULL;
static char *auth_sock_dir = NULL; /* only set if directory needs cleanup */

/* removes the agent forwarding socket */

static void
auth_sock_cleanup_proc(struct passwd *pw)
{
  if (auth_sock_name != NULL) {
    temporarily_use_uid(pw);
    agent_listener_cleanup(options.agent_socket_path,
        auth_sock_name, auth_sock_dir);
    free(auth_sock_name);
    auth_sock_name = NULL;
    restore_uid();
  }
}

static int
auth_input_request_forwarding(struct ssh *ssh, struct passwd *pw, int agent_new)
{
  Channel *nc;
  int sock = -1;

  if (auth_sock_name != NULL) {
    error("authentication forwarding requested twice.");
    return 0;
  }

  /* Temporarily drop privileged uid for mkdir/bind. */
  temporarily_use_uid(pw);

  if (agent_listener(options.agent_socket_path, pw->pw_name, pw->pw_uid,
      pw->pw_dir, getpid(), "sshd", &sock, &auth_sock_name,
      &auth_sock_dir) != 0) {
    /* a more detailed error is already logged */
    ssh_packet_send_debug(ssh, "Agent forwarding disabled: "
        "couldn't create listener socket");
    restore_uid();
    goto authsock_err;
  }
  restore_uid();

  /* Allocate a channel for the authentication agent socket. */
  nc = channel_new(ssh, "auth-listener",
      SSH_CHANNEL_AUTH_SOCKET, sock, sock, -1,
      CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
      0, "auth socket", 1);
  nc->path = xstrdup(auth_sock_name);
  nc->agent_new = agent_new;
  return 1;

 authsock_err:
  free(auth_sock_name);
  if (sock != -1)
    close(sock);
  auth_sock_name = NULL;
  return 0;
}

static void
display_loginmsg(void)
{
  int r;

  if (sshbuf_len(loginmsg) == 0)
    return;
  if ((r = sshbuf_put_u8(loginmsg, 0)) != 0)
    fatal_fr(r, "sshbuf_put_u8");
  printf("%s", (char *)sshbuf_ptr(loginmsg));
  sshbuf_reset(loginmsg);
}

static void
prepare_auth_info_file(struct passwd *pw, struct sshbuf *info)
{
  int fd = -1, success = 0;

  if (!options.expose_userauth_info || info == NULL)
    return;

  temporarily_use_uid(pw);
  auth_info_file = xstrdup("/tmp/sshauth.XXXXXXXXXXXXXXX");
  if ((fd = mkstemp(auth_info_file)) == -1) {
    error_f("mkstemp: %s", strerror(errno));
    goto out;
  }
  if (atomicio(vwrite, fd, sshbuf_mutable_ptr(info),
      sshbuf_len(info)) != sshbuf_len(info)) {
    error_f("write: %s", strerror(errno));
    goto out;
  }
  if (close(fd) != 0) {
    error_f("close: %s", strerror(errno));
    goto out;
  }
  success = 1;
 out:
  if (!success) {
    if (fd != -1)
      close(fd);
    free(auth_info_file);
    auth_info_file = NULL;
  }
  restore_uid();
}

static void
set_fwdpermit_from_authopts(struct ssh *ssh, const struct sshauthopt *opts)
{
  char *tmp, *cp, *host;
  int port;
  size_t i;

  if ((options.allow_tcp_forwarding & FORWARD_LOCAL) != 0) {
    channel_clear_permission(ssh, FORWARD_USER, FORWARD_LOCAL);
    for (i = 0; i < auth_opts->npermitopen; i++) {
      tmp = cp = xstrdup(auth_opts->permitopen[i]);
      /* This shouldn't fail as it has already been checked */
      if ((host = hpdelim2(&cp, NULL)) == NULL)
        fatal_f("internal error: hpdelim");
      host = cleanhostname(host);
      if (cp == NULL || (port = permitopen_port(cp)) < 0)
        fatal_f("internal error: permitopen port");
      channel_add_permission(ssh,
          FORWARD_USER, FORWARD_LOCAL, host, port);
      free(tmp);
    }
  }
  if ((options.allow_tcp_forwarding & FORWARD_REMOTE) != 0) {
    channel_clear_permission(ssh, FORWARD_USER, FORWARD_REMOTE);
    for (i = 0; i < auth_opts->npermitlisten; i++) {
      tmp = cp = xstrdup(auth_opts->permitlisten[i]);
      /* This shouldn't fail as it has already been checked */
      if ((host = hpdelim(&cp)) == NULL)
        fatal_f("internal error: hpdelim");
      host = cleanhostname(host);
      if (cp == NULL || (port = permitopen_port(cp)) < 0)
        fatal_f("internal error: permitlisten port");
      channel_add_permission(ssh,
          FORWARD_USER, FORWARD_REMOTE, host, port);
      free(tmp);
    }
  }
}

void
do_authenticated(struct ssh *ssh, Authctxt *authctxt)
{
  setproctitle("%s", authctxt->pw->pw_name);

  auth_log_authopts("active", auth_opts, 0);

  /* set up the channel layer */
  /* XXX - streamlocal? */
  set_fwdpermit_from_authopts(ssh, auth_opts);

  if (!auth_opts->permit_port_forwarding_flag ||
      options.disable_forwarding) {
    channel_disable_admin(ssh, FORWARD_LOCAL);
    channel_disable_admin(ssh, FORWARD_REMOTE);
  } else {
    if ((options.allow_tcp_forwarding & FORWARD_LOCAL) == 0)
      channel_disable_admin(ssh, FORWARD_LOCAL);
    else
      channel_permit_all(ssh, FORWARD_LOCAL);
    if ((options.allow_tcp_forwarding & FORWARD_REMOTE) == 0)
      channel_disable_admin(ssh, FORWARD_REMOTE);
    else
      channel_permit_all(ssh, FORWARD_REMOTE);
  }
  auth_debug_send(ssh);

  prepare_auth_info_file(authctxt->pw, authctxt->session_info);

  do_authenticated2(ssh, authctxt);

  do_cleanup(ssh, authctxt);
}

/* Check untrusted xauth strings for metacharacters */
static int
xauth_valid_string(const char *s)
{
  size_t i;

  for (i = 0; s[i] != '\0'; i++) {
    if (!isalnum((u_char)s[i]) &&
        s[i] != '.' && s[i] != ':' && s[i] != '/' &&
        s[i] != '-' && s[i] != '_')
      return 0;
  }
  return 1;
}

#define USE_PIPES 1
/*
 * This is called to fork and execute a command when we have no tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors and such.
 */
int
do_exec_no_pty(struct ssh *ssh, Session *s, const char *command)
{
  pid_t pid;
#ifdef USE_PIPES
  int pin[2], pout[2], perr[2];

  if (s == NULL)
    fatal("do_exec_no_pty: no session");

  /* Allocate pipes for communicating with the program. */
  if (pipe(pin) == -1) {
    error_f("pipe in: %.100s", strerror(errno));
    return -1;
  }
  if (pipe(pout) == -1) {
    error_f("pipe out: %.100s", strerror(errno));
    close(pin[0]);
    close(pin[1]);
    return -1;
  }
  if (pipe(perr) == -1) {
    error_f("pipe err: %.100s", strerror(errno));
    close(pin[0]);
    close(pin[1]);
    close(pout[0]);
    close(pout[1]);
    return -1;
  }
#else
  int inout[2], err[2];

  if (s == NULL)
    fatal("do_exec_no_pty: no session");

  /* Uses socket pairs to communicate with the program. */
  if (socketpair(AF_UNIX, SOCK_STREAM, 0, inout) == -1) {
    error_f("socketpair #1: %.100s", strerror(errno));
    return -1;
  }
  if (socketpair(AF_UNIX, SOCK_STREAM, 0, err) == -1) {
    error_f("socketpair #2: %.100s", strerror(errno));
    close(inout[0]);
    close(inout[1]);
    return -1;
  }
#endif

  session_proctitle(s);

  /* Fork the child. */
  switch ((pid = fork())) {
  case -1:
    error_f("fork: %.100s", strerror(errno));
#ifdef USE_PIPES
    close(pin[0]);
    close(pin[1]);
    close(pout[0]);
    close(pout[1]);
    close(perr[0]);
    close(perr[1]);
#else
    close(inout[0]);
    close(inout[1]);
    close(err[0]);
    close(err[1]);
#endif
    return -1;
  case 0:
    is_child = 1;

    /*
     * Create a new session and process group since the 4.4BSD
     * setlogin() affects the entire process group.
     */
    if (setsid() == -1)
      error("setsid failed: %.100s", strerror(errno));

#ifdef USE_PIPES
    /*
     * Redirect stdin.  We close the parent side of the socket
     * pair, and make the child side the standard input.
     */
    close(pin[1]);
    if (dup2(pin[0], 0) == -1)
      perror("dup2 stdin");
    close(pin[0]);

    /* Redirect stdout. */
    close(pout[0]);
    if (dup2(pout[1], 1) == -1)
      perror("dup2 stdout");
    close(pout[1]);

    /* Redirect stderr. */
    close(perr[0]);
    if (dup2(perr[1], 2) == -1)
      perror("dup2 stderr");
    close(perr[1]);
#else
    /*
     * Redirect stdin, stdout, and stderr.  Stdin and stdout will
     * use the same socket, as some programs (particularly rdist)
     * seem to depend on it.
     */
    close(inout[1]);
    close(err[1]);
    if (dup2(inout[0], 0) == -1)  /* stdin */
      perror("dup2 stdin");
    if (dup2(inout[0], 1) == -1)  /* stdout (same as stdin) */
      perror("dup2 stdout");
    close(inout[0]);
    if (dup2(err[0], 2) == -1)  /* stderr */
      perror("dup2 stderr");
    close(err[0]);
#endif

    /* Do processing for the child (exec command etc). */
    do_child(ssh, s, command);
    /* NOTREACHED */
  default:
    break;
  }

#ifdef HAVE_CYGWIN
  cygwin_set_impersonation_token(INVALID_HANDLE_VALUE);
#endif

  s->pid = pid;

  /*
   * Clear loginmsg, since it's the child's responsibility to display
   * it to the user, otherwise multiple sessions may accumulate
   * multiple copies of the login messages.
   */
  sshbuf_reset(loginmsg);

#ifdef USE_PIPES
  /* We are the parent.  Close the child sides of the pipes. */
  close(pin[0]);
  close(pout[1]);
  close(perr[1]);

  session_set_fds(ssh, s, pin[1], pout[0], perr[0],
      s->is_subsystem, 0);
#else
  /* We are the parent.  Close the child sides of the socket pairs. */
  close(inout[0]);
  close(err[0]);

  /*
   * Enter the interactive session.  Note: server_loop must be able to
   * handle the case that fdin and fdout are the same.
   */
  session_set_fds(ssh, s, inout[1], inout[1], err[1],
      s->is_subsystem, 0);
#endif
  return 0;
}

/*
 * This is called to fork and execute a command when we have a tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors, controlling tty, updating wtmp, utmp,
 * lastlog, and other such operations.
 */
int
do_exec_pty(struct ssh *ssh, Session *s, const char *command)
{
  int fdout, ptyfd, ttyfd, ptymaster;
  pid_t pid;

  if (s == NULL)
    fatal("do_exec_pty: no session");
  ptyfd = s->ptyfd;
  ttyfd = s->ttyfd;

  /*
   * Create another descriptor of the pty master side for use as the
   * standard input.  We could use the original descriptor, but this
   * simplifies code in server_loop.  The descriptor is bidirectional.
   * Do this before forking (and cleanup in the child) so as to
   * detect and gracefully fail out-of-fd conditions.
   */
  if ((fdout = dup(ptyfd)) == -1) {
    error_f("dup #1: %s", strerror(errno));
    close(ttyfd);
    close(ptyfd);
    return -1;
  }
  /* we keep a reference to the pty master */
  if ((ptymaster = dup(ptyfd)) == -1) {
    error_f("dup #2: %s", strerror(errno));
    close(ttyfd);
    close(ptyfd);
    close(fdout);
    return -1;
  }

  /* Fork the child. */
  switch ((pid = fork())) {
  case -1:
    error_f("fork: %.100s", strerror(errno));
    close(fdout);
    close(ptymaster);
    close(ttyfd);
    close(ptyfd);
    return -1;
  case 0:
    is_child = 1;

    close(fdout);
    close(ptymaster);

    /* Close the master side of the pseudo tty. */
    close(ptyfd);

    /* Make the pseudo tty our controlling tty. */
    pty_make_controlling_tty(&ttyfd, s->tty);

    /* Redirect stdin/stdout/stderr from the pseudo tty. */
    if (dup2(ttyfd, 0) == -1)
      error("dup2 stdin: %s", strerror(errno));
    if (dup2(ttyfd, 1) == -1)
      error("dup2 stdout: %s", strerror(errno));
    if (dup2(ttyfd, 2) == -1)
      error("dup2 stderr: %s", strerror(errno));

    /* Close the extra descriptor for the pseudo tty. */
    close(ttyfd);

    /* record login, etc. similar to login(1) */
#ifndef HAVE_OSF_SIA
    do_login(ssh, s, command);
#endif
    /*
     * Do common processing for the child, such as execing
     * the command.
     */
    do_child(ssh, s, command);
    /* NOTREACHED */
  default:
    break;
  }

#ifdef HAVE_CYGWIN
  cygwin_set_impersonation_token(INVALID_HANDLE_VALUE);
#endif

  s->pid = pid;

  /* Parent.  Close the slave side of the pseudo tty. */
  close(ttyfd);

  /* Enter interactive session. */
  s->ptymaster = ptymaster;
  session_set_fds(ssh, s, ptyfd, fdout, -1, 1, 1);
  return 0;
}

/*
 * This is called to fork and execute a command.  If another command is
 * to be forced, execute that instead.
 */
int
do_exec(struct ssh *ssh, Session *s, const char *command)
{
  int ret;
  const char *forced = NULL, *tty = NULL;
  char session_type[1024];

  if (options.adm_forced_command) {
    original_command = command;
    command = options.adm_forced_command;
    forced = "(config)";
  } else if (auth_opts->force_command != NULL) {
    original_command = command;
    command = auth_opts->force_command;
    forced = "(key-option)";
  }
  s->forced = 0;
  if (forced != NULL) {
    s->forced = 1;
    if (IS_INTERNAL_SFTP(command)) {
      s->is_subsystem = s->is_subsystem ?
          SUBSYSTEM_INT_SFTP : SUBSYSTEM_INT_SFTP_ERROR;
    } else if (s->is_subsystem)
      s->is_subsystem = SUBSYSTEM_EXT;
    snprintf(session_type, sizeof(session_type),
        "forced-command %s '%.900s'", forced, command);
  } else if (s->is_subsystem) {
    snprintf(session_type, sizeof(session_type),
        "subsystem '%.900s'", s->subsys);
  } else if (command == NULL) {
    snprintf(session_type, sizeof(session_type), "shell");
  } else {
    /* NB. we don't log unforced commands to preserve privacy */
    snprintf(session_type, sizeof(session_type), "command");
  }

  if (s->ttyfd != -1) {
    tty = s->tty;
    if (strncmp(tty, "/dev/", 5) == 0)
      tty += 5;
  }

  verbose("Starting session: %s%s%s for %s from %.200s port %d id %d",
      session_type,
      tty == NULL ? "" : " on ",
      tty == NULL ? "" : tty,
      s->pw->pw_name,
      ssh_remote_ipaddr(ssh),
      ssh_remote_port(ssh),
      s->self);

#ifdef SSH_AUDIT_EVENTS
  if (command != NULL)
    mm_audit_run_command(command);
  else if (s->ttyfd == -1) {
    char *shell = s->pw->pw_shell;

    if (shell[0] == '\0') /* empty shell means /bin/sh */
      shell =_PATH_BSHELL;
    mm_audit_run_command(shell);
  }
#endif
  if (s->ttyfd != -1)
    ret = do_exec_pty(ssh, s, command);
  else
    ret = do_exec_no_pty(ssh, s, command);

  original_command = NULL;

  /*
   * Clear loginmsg: it's the child's responsibility to display
   * it to the user, otherwise multiple sessions may accumulate
   * multiple copies of the login messages.
   */
  sshbuf_reset(loginmsg);

  return ret;
}

/* administrative, login(1)-like work */
void
do_login(struct ssh *ssh, Session *s, const char *command)
{
  socklen_t fromlen;
  struct sockaddr_storage from;

  /*
   * Get IP address of client. If the connection is not a socket, let
   * the address be 0.0.0.0.
   */
  memset(&from, 0, sizeof(from));
  fromlen = sizeof(from);
  if (ssh_packet_connection_is_on_socket(ssh)) {
    if (getpeername(ssh_packet_get_connection_in(ssh),
        (struct sockaddr *)&from, &fromlen) == -1) {
      debug("getpeername: %.100s", strerror(errno));
      cleanup_exit(255);
    }
  }

  if (check_quietlogin(s, command))
    return;

  display_loginmsg();

  do_motd();
}

/*
 * Display the message of the day.
 */
void
do_motd(void)
{
  FILE *f;
  char buf[256];

  if (options.print_motd) {
#ifdef HAVE_LOGIN_CAP
    f = fopen(login_getcapstr(lc, "welcome", "/etc/motd",
        "/etc/motd"), "r");
#else
    f = fopen("/etc/motd", "r");
#endif
    if (f) {
      while (fgets(buf, sizeof(buf), f))
        fputs(buf, stdout);
      fclose(f);
    }
  }
}


/*
 * Check for quiet login, either .hushlogin or command given.
 */
int
check_quietlogin(Session *s, const char *command)
{
  char buf[256];
  struct passwd *pw = s->pw;
  struct stat st;

  /* Return 1 if .hushlogin exists or a command given. */
  if (command != NULL)
    return 1;
  snprintf(buf, sizeof(buf), "%.200s/.hushlogin", pw->pw_dir);
#ifdef HAVE_LOGIN_CAP
  if (login_getcapbool(lc, "hushlogin", 0) || stat(buf, &st) >= 0)
    return 1;
#else
  if (stat(buf, &st) >= 0)
    return 1;
#endif
  return 0;
}

/*
 * Reads environment variables from the given file and adds/overrides them
 * into the environment.  If the file does not exist, this does nothing.
 * Otherwise, it must consist of empty lines, comments (line starts with '#')
 * and assignments of the form name=value.  No other forms are allowed.
 * If allowlist is not NULL, then it is interpreted as a pattern list and
 * only variable names that match it will be accepted.
 */
static void
read_environment_file(char ***env, u_int *envsize,
  const char *filename, const char *allowlist)
{
  FILE *f;
  char *line = NULL, *cp, *value;
  size_t linesize = 0;
  u_int lineno = 0;

  f = fopen(filename, "r");
  if (!f)
    return;

  while (getline(&line, &linesize, f) != -1) {
    if (++lineno > 1000)
      fatal("Too many lines in environment file %s", filename);
    for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
      ;
    if (!*cp || *cp == '#' || *cp == '\n')
      continue;

    cp[strcspn(cp, "\n")] = '\0';

    value = strchr(cp, '=');
    if (value == NULL) {
      fprintf(stderr, "Bad line %u in %.100s\n", lineno,
          filename);
      continue;
    }
    /*
     * Replace the equals sign by nul, and advance value to
     * the value string.
     */
    *value = '\0';
    value++;
    if (allowlist != NULL &&
        match_pattern_list(cp, allowlist, 0) != 1)
      continue;
    child_set_env(env, envsize, cp, value);
  }
  free(line);
  fclose(f);
}

#ifdef HAVE_ETC_DEFAULT_LOGIN
/*
 * Return named variable from specified environment, or NULL if not present.
 */
static char *
child_get_env(char **env, const char *name)
{
  int i;
  size_t len;

  len = strlen(name);
  for (i=0; env[i] != NULL; i++)
    if (strncmp(name, env[i], len) == 0 && env[i][len] == '=')
      return(env[i] + len + 1);
  return NULL;
}

/*
 * Read /etc/default/login.
 * We pick up the PATH (or SUPATH for root) and UMASK.
 */
static void
read_etc_default_login(char ***env, u_int *envsize, uid_t uid)
{
  char **tmpenv = NULL, *var;
  u_int i, tmpenvsize = 0;
  u_long mask;

  /*
   * We don't want to copy the whole file to the child's environment,
   * so we use a temporary environment and copy the variables we're
   * interested in.
   */
  read_environment_file(&tmpenv, &tmpenvsize, "/etc/default/login",
      options.permit_user_env_allowlist);

  if (tmpenv == NULL)
    return;

  if (uid == 0)
    var = child_get_env(tmpenv, "SUPATH");
  else
    var = child_get_env(tmpenv, "PATH");
  if (var != NULL)
    child_set_env(env, envsize, "PATH", var);

  if ((var = child_get_env(tmpenv, "UMASK")) != NULL)
    if (sscanf(var, "%5lo", &mask) == 1)
      umask((mode_t)mask);

  for (i = 0; tmpenv[i] != NULL; i++)
    free(tmpenv[i]);
  free(tmpenv);
}
#endif /* HAVE_ETC_DEFAULT_LOGIN */

#if defined(USE_PAM) || defined(HAVE_CYGWIN)
static void
copy_environment_denylist(char **source, char ***env, u_int *envsize,
    const char *denylist)
{
  char *var_name, *var_val;
  int i;

  if (source == NULL)
    return;

  for(i = 0; source[i] != NULL; i++) {
    var_name = xstrdup(source[i]);
    if ((var_val = strstr(var_name, "=")) == NULL) {
      free(var_name);
      continue;
    }
    *var_val++ = '\0';

    if (denylist == NULL ||
        match_pattern_list(var_name, denylist, 0) != 1) {
      debug3("Copy environment: %s=%s", var_name, var_val);
      child_set_env(env, envsize, var_name, var_val);
    }

    free(var_name);
  }
}
#endif /* defined(USE_PAM) || defined(HAVE_CYGWIN) */

#ifdef HAVE_CYGWIN
static void
copy_environment(char **source, char ***env, u_int *envsize)
{
  copy_environment_denylist(source, env, envsize, NULL);
}
#endif

static char **
do_setup_env(struct ssh *ssh, Session *s, const char *shell)
{
  char buf[256];
  size_t n;
  u_int i, envsize;
  char *ocp, *cp, *value, **env, *laddr;
  struct passwd *pw = s->pw;
#if !defined (HAVE_LOGIN_CAP) && !defined (HAVE_CYGWIN)
  char *path = NULL;
#endif

  /* Initialize the environment. */
  envsize = 100;
  env = xcalloc(envsize, sizeof(char *));
  env[0] = NULL;

#ifdef HAVE_CYGWIN
  /*
   * The Windows environment contains some setting which are
   * important for a running system. They must not be dropped.
   */
  {
    char **p;

    p = fetch_windows_environment();
    copy_environment(p, &env, &envsize);
    free_windows_environment(p);
  }
#endif

#ifdef GSSAPI
  /* Allow any GSSAPI methods that we've used to alter
   * the child's environment as they see fit
   */
  ssh_gssapi_do_child(&env, &envsize);
#endif

  /* Set basic environment. */
  for (i = 0; i < s->num_env; i++)
    child_set_env(&env, &envsize, s->env[i].name, s->env[i].val);

  child_set_env(&env, &envsize, "USER", pw->pw_name);
  child_set_env(&env, &envsize, "LOGNAME", pw->pw_name);
#ifdef _AIX
  child_set_env(&env, &envsize, "LOGIN", pw->pw_name);
#endif
  child_set_env(&env, &envsize, "HOME", pw->pw_dir);
#ifdef HAVE_LOGIN_CAP
  if (setusercontext(lc, pw, pw->pw_uid, LOGIN_SETPATH) < 0)
    child_set_env(&env, &envsize, "PATH", _PATH_STDPATH);
  else
    child_set_env(&env, &envsize, "PATH", getenv("PATH"));
#else /* HAVE_LOGIN_CAP */
# ifndef HAVE_CYGWIN
  /*
   * There's no standard path on Windows. The path contains
   * important components pointing to the system directories,
   * needed for loading shared libraries. So the path better
   * remains intact here.
   */
#  ifdef HAVE_ETC_DEFAULT_LOGIN
  read_etc_default_login(&env, &envsize, pw->pw_uid);
  path = child_get_env(env, "PATH");
#  endif /* HAVE_ETC_DEFAULT_LOGIN */
  if (path == NULL || *path == '\0') {
    child_set_env(&env, &envsize, "PATH",
        s->pw->pw_uid == 0 ?  SUPERUSER_PATH : _PATH_STDPATH);
  }
# endif /* HAVE_CYGWIN */
#endif /* HAVE_LOGIN_CAP */

  if (!options.use_pam) {
    snprintf(buf, sizeof buf, "%.200s/%.50s",
        _PATH_MAILDIR, pw->pw_name);
    child_set_env(&env, &envsize, "MAIL", buf);
  }

  /* Normal systems set SHELL by default. */
  child_set_env(&env, &envsize, "SHELL", shell);

  if (getenv("TZ"))
    child_set_env(&env, &envsize, "TZ", getenv("TZ"));
#ifdef HAVE_LOGIN_CAP
  if (getenv("XDG_RUNTIME_DIR")) {
    child_set_env(&env, &envsize, "XDG_RUNTIME_DIR",
        getenv("XDG_RUNTIME_DIR"));
  }
#endif /* HAVE_LOGIN_CAP */
  if (s->term)
    child_set_env(&env, &envsize, "TERM", s->term);
  if (s->display)
    child_set_env(&env, &envsize, "DISPLAY", s->display);

  /*
   * Since we clear KRB5CCNAME at startup, if it's set now then it
   * must have been set by a native authentication method (eg AIX or
   * SIA), so copy it to the child.
   */
  {
    char *cp;

    if ((cp = getenv("KRB5CCNAME")) != NULL)
      child_set_env(&env, &envsize, "KRB5CCNAME", cp);
  }

#ifdef _AIX
  {
    char *cp;

    if ((cp = getenv("AUTHSTATE")) != NULL)
      child_set_env(&env, &envsize, "AUTHSTATE", cp);
    read_environment_file(&env, &envsize, "/etc/environment",
        options.permit_user_env_allowlist);
  }
#endif
#ifdef KRB5
  if (s->authctxt->krb5_ccname)
    child_set_env(&env, &envsize, "KRB5CCNAME",
        s->authctxt->krb5_ccname);
#endif
  if (auth_sock_name != NULL)
    child_set_env(&env, &envsize, SSH_AUTHSOCKET_ENV_NAME,
        auth_sock_name);


  /* Set custom environment options from pubkey authentication. */
  if (options.permit_user_env) {
    for (n = 0 ; n < auth_opts->nenv; n++) {
      ocp = xstrdup(auth_opts->env[n]);
      cp = strchr(ocp, '=');
      if (cp != NULL) {
        *cp = '\0';
        /* Apply PermitUserEnvironment allowlist */
        if (options.permit_user_env_allowlist == NULL ||
            match_pattern_list(ocp,
            options.permit_user_env_allowlist, 0) == 1)
          child_set_env(&env, &envsize,
              ocp, cp + 1);
      }
      free(ocp);
    }
  }

  /* read $HOME/.ssh/environment. */
  if (options.permit_user_env) {
    snprintf(buf, sizeof buf, "%.200s/%s/environment",
        pw->pw_dir, _PATH_SSH_USER_DIR);
    read_environment_file(&env, &envsize, buf,
        options.permit_user_env_allowlist);
  }

#ifdef USE_PAM
  /*
   * Pull in any environment variables that may have
   * been set by PAM.
   */
  if (options.use_pam) {
    char **p;

    /*
     * Don't allow PAM-internal env vars to leak
     * back into the session environment.
     */
#define PAM_ENV_DENYLIST  "SSH_AUTH_INFO*,SSH_CONNECTION*"
    p = fetch_pam_child_environment();
    copy_environment_denylist(p, &env, &envsize,
        PAM_ENV_DENYLIST);
    free_pam_environment(p);

    p = fetch_pam_environment();
    copy_environment_denylist(p, &env, &envsize,
        PAM_ENV_DENYLIST);
    free_pam_environment(p);
  }
#endif /* USE_PAM */

  /* Environment specified by admin */
  for (i = 0; i < options.num_setenv; i++) {
    cp = xstrdup(options.setenv[i]);
    if ((value = strchr(cp, '=')) == NULL) {
      /* shouldn't happen; vars are checked in servconf.c */
      fatal("Invalid config SetEnv: %s", options.setenv[i]);
    }
    *value++ = '\0';
    child_set_env(&env, &envsize, cp, value);
    free(cp);
  }

  /* SSH_CLIENT deprecated */
  snprintf(buf, sizeof buf, "%.50s %d %d",
      ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
      ssh_local_port(ssh));
  child_set_env(&env, &envsize, "SSH_CLIENT", buf);

  laddr = get_local_ipaddr(ssh_packet_get_connection_in(ssh));
  snprintf(buf, sizeof buf, "%.50s %d %.50s %d",
      ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
      laddr, ssh_local_port(ssh));
  free(laddr);
  child_set_env(&env, &envsize, "SSH_CONNECTION", buf);

  if (tun_fwd_ifnames != NULL)
    child_set_env(&env, &envsize, "SSH_TUNNEL", tun_fwd_ifnames);
  if (auth_info_file != NULL)
    child_set_env(&env, &envsize, "SSH_USER_AUTH", auth_info_file);
  if (s->ttyfd != -1)
    child_set_env(&env, &envsize, "SSH_TTY", s->tty);
  if (original_command)
    child_set_env(&env, &envsize, "SSH_ORIGINAL_COMMAND",
        original_command);

  if (debug_flag) {
    /* dump the environment */
    fprintf(stderr, "Environment:\n");
    for (i = 0; env[i]; i++)
      fprintf(stderr, "  %.200s\n", env[i]);
  }
  return env;
}

/*
 * Run $HOME/.ssh/rc, /etc/ssh/sshrc, or xauth (whichever is found
 * first in this order).
 */
static void
do_rc_files(struct ssh *ssh, Session *s, const char *shell)
{
  FILE *f = NULL;
  char *cmd = NULL, *user_rc = NULL;
  int do_xauth;
  struct stat st;

  do_xauth =
      s->display != NULL && s->auth_proto != NULL && s->auth_data != NULL;
  xasprintf(&user_rc, "%s/%s", s->pw->pw_dir, _PATH_SSH_USER_RC);

  /* ignore _PATH_SSH_USER_RC for subsystems and admin forced commands */
  if (!s->is_subsystem && options.adm_forced_command == NULL &&
      auth_opts->permit_user_rc && options.permit_user_rc &&
      stat(user_rc, &st) >= 0) {
    if (xasprintf(&cmd, "%s -c '%s %s'", shell, _PATH_BSHELL,
        user_rc) == -1)
      fatal_f("xasprintf: %s", strerror(errno));
    if (debug_flag)
      fprintf(stderr, "Running %s\n", cmd);
    f = popen(cmd, "w");
    if (f) {
      if (do_xauth)
        fprintf(f, "%s %s\n", s->auth_proto,
            s->auth_data);
      pclose(f);
    } else
      fprintf(stderr, "Could not run %s\n",
          user_rc);
  } else if (stat(_PATH_SSH_SYSTEM_RC, &st) >= 0) {
    if (debug_flag)
      fprintf(stderr, "Running %s %s\n", _PATH_BSHELL,
          _PATH_SSH_SYSTEM_RC);
    f = popen(_PATH_BSHELL " " _PATH_SSH_SYSTEM_RC, "w");
    if (f) {
      if (do_xauth)
        fprintf(f, "%s %s\n", s->auth_proto,
            s->auth_data);
      pclose(f);
    } else
      fprintf(stderr, "Could not run %s\n",
          _PATH_SSH_SYSTEM_RC);
  } else if (do_xauth && options.xauth_location != NULL) {
    /* Add authority data to .Xauthority if appropriate. */
    if (debug_flag) {
      fprintf(stderr,
          "Running %.500s remove %.100s\n",
          options.xauth_location, s->auth_display);
      fprintf(stderr,
          "%.500s add %.100s %.100s %.100s\n",
          options.xauth_location, s->auth_display,
          s->auth_proto, s->auth_data);
    }
    if (xasprintf(&cmd, "%s -q -", options.xauth_location) == -1)
      fatal_f("xasprintf: %s", strerror(errno));
    f = popen(cmd, "w");
    if (f) {
      fprintf(f, "remove %s\n",
          s->auth_display);
      fprintf(f, "add %s %s %s\n",
          s->auth_display, s->auth_proto,
          s->auth_data);
      pclose(f);
    } else {
      fprintf(stderr, "Could not run %s\n",
          cmd);
    }
  }
  free(cmd);
  free(user_rc);
}

static void
do_nologin(struct passwd *pw)
{
  FILE *f = NULL;
  char buf[1024], *nl, *def_nl = _PATH_NOLOGIN;
  struct stat sb;

#ifdef HAVE_LOGIN_CAP
  if (login_getcapbool(lc, "ignorenologin", 0) || pw->pw_uid == 0)
    return;
  nl = login_getcapstr(lc, "nologin", def_nl, def_nl);
#else
  if (pw->pw_uid == 0)
    return;
  nl = def_nl;
#endif
  if (stat(nl, &sb) == -1)
    return;

  /* /etc/nologin exists.  Print its contents if we can and exit. */
  logit("User %.100s not allowed because %s exists", pw->pw_name, nl);
  if ((f = fopen(nl, "r")) != NULL) {
    while (fgets(buf, sizeof(buf), f))
      fputs(buf, stderr);
    fclose(f);
  }
  exit(254);
}

/*
 * Chroot into a directory after checking it for safety: all path components
 * must be root-owned directories with strict permissions.
 */
static void
safely_chroot(const char *path, uid_t uid)
{
  const char *cp;
  char component[PATH_MAX];
  struct stat st;

  if (!path_absolute(path))
    fatal("chroot path does not begin at root");
  if (strlen(path) >= sizeof(component))
    fatal("chroot path too long");

  /*
   * Descend the path, checking that each component is a
   * root-owned directory with strict permissions.
   */
  for (cp = path; cp != NULL;) {
    if ((cp = strchr(cp, '/')) == NULL)
      strlcpy(component, path, sizeof(component));
    else {
      cp++;
      memcpy(component, path, cp - path);
      component[cp - path] = '\0';
    }

    debug3_f("checking '%s'", component);

    if (stat(component, &st) != 0)
      fatal_f("stat(\"%s\"): %s",
          component, strerror(errno));
    if (st.st_uid != 0 || (st.st_mode & 022) != 0)
      fatal("bad ownership or modes for chroot "
          "directory %s\"%s\"",
          cp == NULL ? "" : "component ", component);
    if (!S_ISDIR(st.st_mode))
      fatal("chroot path %s\"%s\" is not a directory",
          cp == NULL ? "" : "component ", component);

  }

  if (chdir(path) == -1)
    fatal("Unable to chdir to chroot path \"%s\": "
        "%s", path, strerror(errno));
  if (chroot(path) == -1)
    fatal("chroot(\"%s\"): %s", path, strerror(errno));
  if (chdir("/") == -1)
    fatal_f("chdir(/) after chroot: %s", strerror(errno));
  verbose("Changed root directory to \"%s\"", path);
}

/* Set login name, uid, gid, and groups. */
void
do_setusercontext(struct passwd *pw)
{
  char uidstr[32], *chroot_path, *tmp;

  platform_setusercontext(pw);

  if (platform_privileged_uidswap()) {
#ifdef HAVE_LOGIN_CAP
    if (setusercontext(lc, pw, pw->pw_uid,
        (LOGIN_SETALL & ~(LOGIN_SETPATH|LOGIN_SETUSER))) < 0) {
      perror("unable to set user context");
      exit(1);
    }
#else
    if (setlogin(pw->pw_name) < 0)
      error("setlogin failed: %s", strerror(errno));
    if (setgid(pw->pw_gid) < 0) {
      perror("setgid");
      exit(1);
    }
    /* Initialize the group list. */
    if (initgroups(pw->pw_name, pw->pw_gid) < 0) {
      perror("initgroups");
      exit(1);
    }
    endgrent();
#endif

    platform_setusercontext_post_groups(pw);

    if (!in_chroot && options.chroot_directory != NULL &&
        strcasecmp(options.chroot_directory, "none") != 0) {
      tmp = tilde_expand_filename(options.chroot_directory,
          pw->pw_uid);
      snprintf(uidstr, sizeof(uidstr), "%llu",
          (unsigned long long)pw->pw_uid);
      chroot_path = percent_expand(tmp, "h", pw->pw_dir,
          "u", pw->pw_name, "U", uidstr, (char *)NULL);
      safely_chroot(chroot_path, pw->pw_uid);
      free(tmp);
      free(chroot_path);
      /* Make sure we don't attempt to chroot again */
      free(options.chroot_directory);
      options.chroot_directory = NULL;
      in_chroot = 1;
    }

#ifdef HAVE_LOGIN_CAP
    if (setusercontext(lc, pw, pw->pw_uid, LOGIN_SETUSER) < 0) {
      perror("unable to set user context (setuser)");
      exit(1);
    }
    /* 
     * FreeBSD's setusercontext() will not apply the user's
     * own umask setting unless running with the user's UID.
     */
    (void) setusercontext(lc, pw, pw->pw_uid, LOGIN_SETUMASK);
#else
# ifdef USE_LIBIAF
    /*
     * In a chroot environment, the set_id() will always fail;
     * typically because of the lack of necessary authentication
     * services and runtime such as ./usr/lib/libiaf.so,
     * ./usr/lib/libpam.so.1, and ./etc/passwd We skip it in the
     * internal sftp chroot case.  We'll lose auditing and ACLs but
     * permanently_set_uid will take care of the rest.
     */
    if (!in_chroot && set_id(pw->pw_name) != 0)
      fatal("set_id(%s) Failed", pw->pw_name);
# endif /* USE_LIBIAF */
    /* Permanently switch to the desired uid. */
    permanently_set_uid(pw);
#endif
  } else if (options.chroot_directory != NULL &&
      strcasecmp(options.chroot_directory, "none") != 0) {
    fatal("server lacks privileges to chroot to ChrootDirectory");
  }

  if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid)
    fatal("Failed to set uids to %u.", (u_int) pw->pw_uid);
}

static void
do_pwchange(Session *s)
{
  fflush(NULL);
  fprintf(stderr, "WARNING: Your password has expired.\n");
  if (s->ttyfd != -1) {
    fprintf(stderr,
        "You must change your password now and log in again!\n");
#ifdef WITH_SELINUX
    setexeccon(NULL);
#endif
#ifdef PASSWD_NEEDS_USERNAME
    execl(_PATH_PASSWD_PROG, "passwd", s->pw->pw_name,
        (char *)NULL);
#else
    execl(_PATH_PASSWD_PROG, "passwd", (char *)NULL);
#endif
    perror("passwd");
  } else {
    fprintf(stderr,
        "Password change required but no TTY available.\n");
  }
  exit(1);
}

static void
child_close_fds(struct ssh *ssh)
{
  extern int auth_sock;

  if (auth_sock != -1) {
    close(auth_sock);
    auth_sock = -1;
  }

  if (ssh_packet_get_connection_in(ssh) ==
      ssh_packet_get_connection_out(ssh))
    close(ssh_packet_get_connection_in(ssh));
  else {
    close(ssh_packet_get_connection_in(ssh));
    close(ssh_packet_get_connection_out(ssh));
  }
  /*
   * Close all descriptors related to channels.  They will still remain
   * open in the parent.
   */
  /* XXX better use close-on-exec? -markus */
  channel_close_all(ssh);

  /*
   * Close any extra file descriptors.  Note that there may still be
   * descriptors left by system functions.  They will be closed later.
   */
  endpwent();

  /* Stop directing logs to a high-numbered fd before we close it */
  log_redirect_stderr_to(NULL);

  /*
   * Close any extra open file descriptors so that we don't have them
   * hanging around in clients.  Note that we want to do this after
   * initgroups, because at least on Solaris 2.3 it leaves file
   * descriptors open.
   */
  closefrom(STDERR_FILENO + 1);
}

/*
 * Performs common processing for the child, such as setting up the
 * environment, closing extra file descriptors, setting the user and group
 * ids, and executing the command or shell.
 */
#define ARGV_MAX 10
void
do_child(struct ssh *ssh, Session *s, const char *command)
{
  extern char **environ;
  char **env, *argv[ARGV_MAX], remote_id[512];
  const char *shell, *shell0;
  struct passwd *pw = s->pw;
  int r = 0;

  sshpkt_fmt_connection_id(ssh, remote_id, sizeof(remote_id));

  /* remove keys from memory */
  ssh_packet_clear_keys(ssh);

  /* Force a password change */
  if (s->authctxt->force_pwchange) {
    do_setusercontext(pw);
    child_close_fds(ssh);
    do_pwchange(s);
    exit(1);
  }

  /*
   * Login(1) does this as well, and it needs uid 0 for the "-h"
   * switch, so we let login(1) to this for us.
   */
#ifdef HAVE_OSF_SIA
  session_setup_sia(pw, s->ttyfd == -1 ? NULL : s->tty);
  if (!check_quietlogin(s, command))
    do_motd();
#else /* HAVE_OSF_SIA */
  /* When PAM is enabled we rely on it to do the nologin check */
  if (!options.use_pam)
    do_nologin(pw);
  do_setusercontext(pw);
  /*
   * PAM session modules in do_setusercontext may have
   * generated messages, so if this in an interactive
   * login then display them too.
   */
  if (!check_quietlogin(s, command))
    display_loginmsg();
#endif /* HAVE_OSF_SIA */

#ifdef USE_PAM
  if (options.use_pam && !is_pam_session_open()) {
    debug3("PAM session not opened, exiting");
    display_loginmsg();
    exit(254);
  }
#endif

  /*
   * Get the shell from the password data.  An empty shell field is
   * legal, and means /bin/sh.
   */
  shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;

  /*
   * Make sure $SHELL points to the shell from the password file,
   * even if shell is overridden from login.conf
   */
  env = do_setup_env(ssh, s, shell);

#ifdef HAVE_LOGIN_CAP
  shell = login_getcapstr(lc, "shell", (char *)shell, (char *)shell);
#endif

  /*
   * Close the connection descriptors; note that this is the child, and
   * the server will still have the socket open, and it is important
   * that we do not shutdown it.  Note that the descriptors cannot be
   * closed before building the environment, as we call
   * ssh_remote_ipaddr there.
   */
  child_close_fds(ssh);

  /*
   * Must take new environment into use so that .ssh/rc,
   * /etc/ssh/sshrc and xauth are run in the proper environment.
   */
  environ = env;

#if defined(KRB5) && defined(USE_AFS)
  /*
   * At this point, we check to see if AFS is active and if we have
   * a valid Kerberos 5 TGT. If so, it seems like a good idea to see
   * if we can (and need to) extend the ticket into an AFS token. If
   * we don't do this, we run into potential problems if the user's
   * home directory is in AFS and it's not world-readable.
   */

  if (options.kerberos_get_afs_token && k_hasafs() &&
      (s->authctxt->krb5_ctx != NULL)) {
    char cell[64];

    debug("Getting AFS token");

    k_setpag();

    if (k_afs_cell_of_file(pw->pw_dir, cell, sizeof(cell)) == 0)
      krb5_afslog(s->authctxt->krb5_ctx,
          s->authctxt->krb5_fwd_ccache, cell, NULL);

    krb5_afslog_home(s->authctxt->krb5_ctx,
        s->authctxt->krb5_fwd_ccache, NULL, NULL, pw->pw_dir);
  }
#endif

  /* Change current directory to the user's home directory. */
  if (chdir(pw->pw_dir) == -1) {
    /* Suppress missing homedir warning for chroot case */
#ifdef HAVE_LOGIN_CAP
    r = login_getcapbool(lc, "requirehome", 0);
#endif
    if (r || !in_chroot) {
      fprintf(stderr, "Could not chdir to home "
          "directory %s: %s\n", pw->pw_dir,
          strerror(errno));
    }
    if (r)
      exit(1);
  }

  closefrom(STDERR_FILENO + 1);

  do_rc_files(ssh, s, shell);

  /* restore SIGPIPE for child */
  ssh_signal(SIGPIPE, SIG_DFL);

  if (s->is_subsystem == SUBSYSTEM_INT_SFTP_ERROR) {
    error("Connection from %s: refusing non-sftp session",
        remote_id);
    printf("This service allows sftp connections only.\n");
    fflush(NULL);
    exit(1);
  } else if (s->is_subsystem == SUBSYSTEM_INT_SFTP) {
    extern int optind, optreset;
    int sftp_argc;
    char **sftp_argv;

    setproctitle("%s@%s", s->pw->pw_name, INTERNAL_SFTP_NAME);
    if (argv_split(command == NULL ? "sftp-server" : command,
        &sftp_argc, &sftp_argv, 1) != 0) {
      error("internal error: can't split internal-sftp "
          "arguments");
      exit(1);
    }
    optind = optreset = 1;
    __progname = sftp_argv[0];
#ifdef WITH_SELINUX
    ssh_selinux_change_context("sftpd_t");
#endif
    exit(sftp_server_main(sftp_argc, sftp_argv, s->pw));
  }

  fflush(NULL);

  /* Get the last component of the shell name. */
  if ((shell0 = strrchr(shell, '/')) != NULL)
    shell0++;
  else
    shell0 = shell;

  /*
   * If we have no command, execute the shell.  In this case, the shell
   * name to be passed in argv[0] is preceded by '-' to indicate that
   * this is a login shell.
   */
  if (!command) {
    char argv0[256];

    /* Start the shell.  Set initial character to '-'. */
    argv0[0] = '-';

    if (strlcpy(argv0 + 1, shell0, sizeof(argv0) - 1)
        >= sizeof(argv0) - 1) {
      errno = EINVAL;
      perror(shell);
      exit(1);
    }

    /* Execute the shell. */
    argv[0] = argv0;
    argv[1] = NULL;
    execve(shell, argv, env);

    /* Executing the shell failed. */
    perror(shell);
    exit(1);
  }
  /*
   * Execute the command using the user's shell.  This uses the -c
   * option to execute the command.
   */
  argv[0] = (char *) shell0;
  argv[1] = "-c";
  argv[2] = (char *) command;
  argv[3] = NULL;
  execve(shell, argv, env);
  perror(shell);
  exit(1);
}

void
session_unused(int id)
{
  debug3_f("session id %d unused", id);
  if (id >= options.max_sessions ||
      id >= sessions_nalloc) {
    fatal_f("insane session id %d (max %d nalloc %d)",
        id, options.max_sessions, sessions_nalloc);
  }
  memset(&sessions[id], 0, sizeof(*sessions));
  sessions[id].self = id;
  sessions[id].used = 0;
  sessions[id].chanid = -1;
  sessions[id].ptyfd = -1;
  sessions[id].ttyfd = -1;
  sessions[id].ptymaster = -1;
  sessions[id].x11_chanids = NULL;
  sessions[id].next_unused = sessions_first_unused;
  sessions_first_unused = id;
}

Session *
session_new(void)
{
  Session *s, *tmp;

  if (sessions_first_unused == -1) {
    if (sessions_nalloc >= options.max_sessions)
      return NULL;
    debug2_f("allocate (allocated %d max %d)",
        sessions_nalloc, options.max_sessions);
    tmp = xrecallocarray(sessions, sessions_nalloc,
        sessions_nalloc + 1, sizeof(*sessions));
    if (tmp == NULL) {
      error_f("cannot allocate %d sessions",
          sessions_nalloc + 1);
      return NULL;
    }
    sessions = tmp;
    session_unused(sessions_nalloc++);
  }

  if (sessions_first_unused >= sessions_nalloc ||
      sessions_first_unused < 0) {
    fatal_f("insane first_unused %d max %d nalloc %d",
        sessions_first_unused, options.max_sessions,
        sessions_nalloc);
  }

  s = &sessions[sessions_first_unused];
  if (s->used)
    fatal_f("session %d already used", sessions_first_unused);
  sessions_first_unused = s->next_unused;
  s->used = 1;
  s->next_unused = -1;
  debug("session_new: session %d", s->self);

  return s;
}

static void
session_dump(void)
{
  int i;
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];

    debug("dump: used %d next_unused %d session %d "
        "channel %d pid %ld",
        s->used,
        s->next_unused,
        s->self,
        s->chanid,
        (long)s->pid);
  }
}

int
session_open(Authctxt *authctxt, int chanid)
{
  Session *s = session_new();
  debug("session_open: channel %d", chanid);
  if (s == NULL) {
    error("no more sessions");
    return 0;
  }
  s->authctxt = authctxt;
  s->pw = authctxt->pw;
  if (s->pw == NULL || !authctxt->valid)
    fatal("no user for session %d", s->self);
  debug("session_open: session %d: link with channel %d", s->self, chanid);
  s->chanid = chanid;
  return 1;
}

Session *
session_by_tty(char *tty)
{
  int i;
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];
    if (s->used && s->ttyfd != -1 && strcmp(s->tty, tty) == 0) {
      debug("session_by_tty: session %d tty %s", i, tty);
      return s;
    }
  }
  debug("session_by_tty: unknown tty %.100s", tty);
  session_dump();
  return NULL;
}

static Session *
session_by_channel(int id)
{
  int i;
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];
    if (s->used && s->chanid == id) {
      debug("session_by_channel: session %d channel %d",
          i, id);
      return s;
    }
  }
  debug("session_by_channel: unknown channel %d", id);
  session_dump();
  return NULL;
}

static Session *
session_by_x11_channel(int id)
{
  int i, j;

  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];

    if (s->x11_chanids == NULL || !s->used)
      continue;
    for (j = 0; s->x11_chanids[j] != -1; j++) {
      if (s->x11_chanids[j] == id) {
        debug("session_by_x11_channel: session %d "
            "channel %d", s->self, id);
        return s;
      }
    }
  }
  debug("session_by_x11_channel: unknown channel %d", id);
  session_dump();
  return NULL;
}

static Session *
session_by_pid(pid_t pid)
{
  int i;
  debug("session_by_pid: pid %ld", (long)pid);
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];
    if (s->used && s->pid == pid)
      return s;
  }
  error("session_by_pid: unknown pid %ld", (long)pid);
  session_dump();
  return NULL;
}

static int
session_window_change_req(struct ssh *ssh, Session *s)
{
  int r;

  if ((r = sshpkt_get_u32(ssh, &s->col)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->row)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->xpixel)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->ypixel)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);
  pty_change_window_size(s->ptyfd, s->row, s->col, s->xpixel, s->ypixel);
  return 1;
}

static int
session_pty_req(struct ssh *ssh, Session *s)
{
  int r;

  if (!auth_opts->permit_pty_flag || !options.permit_tty) {
    debug("Allocating a pty not permitted for this connection.");
    return 0;
  }
  if (s->ttyfd != -1) {
    ssh_packet_disconnect(ssh, "Protocol error: you already have a pty.");
    return 0;
  }

  if ((r = sshpkt_get_cstring(ssh, &s->term, NULL)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->col)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->row)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->xpixel)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->ypixel)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  if (strcmp(s->term, "") == 0) {
    free(s->term);
    s->term = NULL;
  }

  /* Allocate a pty and open it. */
  debug("Allocating pty.");
  if (!mm_pty_allocate(&s->ptyfd, &s->ttyfd, s->tty, sizeof(s->tty))) {
    free(s->term);
    s->term = NULL;
    s->ptyfd = -1;
    s->ttyfd = -1;
    error("session_pty_req: session %d alloc failed", s->self);
    return 0;
  }
  debug("session_pty_req: session %d alloc %s", s->self, s->tty);

  ssh_tty_parse_modes(ssh, s->ttyfd);

  if ((r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  /* Set window size from the packet. */
  pty_change_window_size(s->ptyfd, s->row, s->col, s->xpixel, s->ypixel);

  session_proctitle(s);
  return 1;
}

static int
session_subsystem_req(struct ssh *ssh, Session *s)
{
  struct stat st;
  int r, success = 0, found = 0;
  char *prog, *cmd, *type;
  u_int i;

  if ((r = sshpkt_get_cstring(ssh, &s->subsys, NULL)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);
  debug2("subsystem request for %.100s by user %s", s->subsys,
      s->pw->pw_name);

  for (i = 0; i < options.num_subsystems; i++) {
    if (strcmp(s->subsys, options.subsystem_name[i]) != 0)
      continue;
    found = 1;
    prog = options.subsystem_command[i];
    cmd = options.subsystem_args[i];
    if (strcmp(INTERNAL_SFTP_NAME, prog) == 0) {
      s->is_subsystem = SUBSYSTEM_INT_SFTP;
      debug("subsystem: %s", prog);
    } else {
      if (stat(prog, &st) == -1)
        debug("subsystem: cannot stat %s: %s",
            prog, strerror(errno));
      s->is_subsystem = SUBSYSTEM_EXT;
      debug("subsystem: exec() %s", cmd);
    }
    xasprintf(&type, "session:subsystem:%s",
        options.subsystem_name[i]);
    channel_set_xtype(ssh, s->chanid, type);
    free(type);
    success = do_exec(ssh, s, cmd) == 0;
    break;
  }

  if (!success) {
    logit("subsystem request for %.100s by user %s failed, %s",
        s->subsys, s->pw->pw_name,
        found ? "execution failed" : "subsystem not found");
  }

  return success;
}

static int
session_x11_req(struct ssh *ssh, Session *s)
{
  int r, success;
  u_char single_connection = 0;

  if (s->auth_proto != NULL || s->auth_data != NULL) {
    error("session_x11_req: session %d: "
        "x11 forwarding already active", s->self);
    return 0;
  }
  if ((r = sshpkt_get_u8(ssh, &single_connection)) != 0 ||
      (r = sshpkt_get_cstring(ssh, &s->auth_proto, NULL)) != 0 ||
      (r = sshpkt_get_cstring(ssh, &s->auth_data, NULL)) != 0 ||
      (r = sshpkt_get_u32(ssh, &s->screen)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  s->single_connection = single_connection;

  if (xauth_valid_string(s->auth_proto) &&
      xauth_valid_string(s->auth_data))
    success = session_setup_x11fwd(ssh, s);
  else {
    success = 0;
    error("Invalid X11 forwarding data");
  }
  if (!success) {
    free(s->auth_proto);
    free(s->auth_data);
    s->auth_proto = NULL;
    s->auth_data = NULL;
  }
  return success;
}

static int
session_shell_req(struct ssh *ssh, Session *s)
{
  int r;

  if ((r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  channel_set_xtype(ssh, s->chanid, "session:shell");

  return do_exec(ssh, s, NULL) == 0;
}

static int
session_exec_req(struct ssh *ssh, Session *s)
{
  u_int success;
  int r;
  char *command = NULL;

  if ((r = sshpkt_get_cstring(ssh, &command, NULL)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  channel_set_xtype(ssh, s->chanid, "session:command");

  success = do_exec(ssh, s, command) == 0;
  free(command);
  return success;
}

static int
session_break_req(struct ssh *ssh, Session *s)
{
  int r;

  if ((r = sshpkt_get_u32(ssh, NULL)) != 0 || /* ignore */
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  if (s->ptymaster == -1 || tcsendbreak(s->ptymaster, 0) == -1)
    return 0;
  return 1;
}

static int
session_env_req(struct ssh *ssh, Session *s)
{
  char *name, *val;
  u_int i;
  int r;

  if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0 ||
      (r = sshpkt_get_cstring(ssh, &val, NULL)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);

  /* Don't set too many environment variables */
  if (s->num_env > 128) {
    debug2("Ignoring env request %s: too many env vars", name);
    goto fail;
  }

  for (i = 0; i < options.num_accept_env; i++) {
    if (match_pattern(name, options.accept_env[i])) {
      debug2("Setting env %d: %s=%s", s->num_env, name, val);
      s->env = xrecallocarray(s->env, s->num_env,
          s->num_env + 1, sizeof(*s->env));
      s->env[s->num_env].name = name;
      s->env[s->num_env].val = val;
      s->num_env++;
      return (1);
    }
  }
  debug2("Ignoring env request %s: disallowed name", name);

 fail:
  free(name);
  free(val);
  return (0);
}

/*
 * Conversion of signals from ssh channel request names.
 * Subset of signals from RFC 4254 section 6.10C, with SIGINFO as
 * local extension.
 */
static int
name2sig(char *name)
{
#define SSH_SIG(x) if (strcmp(name, #x) == 0) return SIG ## x
  SSH_SIG(HUP);
  SSH_SIG(INT);
  SSH_SIG(KILL);
  SSH_SIG(QUIT);
  SSH_SIG(TERM);
  SSH_SIG(USR1);
  SSH_SIG(USR2);
#undef  SSH_SIG
#ifdef SIGINFO
  if (strcmp(name, "INFO@openssh.com") == 0)
    return SIGINFO;
#endif
  return -1;
}

static int
session_signal_req(struct ssh *ssh, Session *s)
{
  char *signame = NULL;
  int r, sig, success = 0;

  if ((r = sshpkt_get_cstring(ssh, &signame, NULL)) != 0 ||
      (r = sshpkt_get_end(ssh)) != 0) {
    error_fr(r, "parse");
    goto out;
  }
  if ((sig = name2sig(signame)) == -1) {
    error_f("unsupported signal \"%s\"", signame);
    goto out;
  }
  if (s->pid <= 0) {
    error_f("no pid for session %d", s->self);
    goto out;
  }
  if (s->forced || s->is_subsystem) {
    error_f("refusing to send signal %s to %s session",
        signame, s->forced ? "forced-command" : "subsystem");
    goto out;
  }

  debug_f("signal %s, killpg(%ld, %d)", signame, (long)s->pid, sig);
  temporarily_use_uid(s->pw);
  r = killpg(s->pid, sig);
  restore_uid();
  if (r != 0) {
    error_f("killpg(%ld, %d): %s", (long)s->pid,
        sig, strerror(errno));
    goto out;
  }

  /* success */
  success = 1;
 out:
  free(signame);
  return success;
}

static int
session_auth_agent_req(struct ssh *ssh, Session *s, int agent_new)
{
  static int called = 0;
  int r;

  if ((r = sshpkt_get_end(ssh)) != 0)
    sshpkt_fatal(ssh, r, "%s: parse packet", __func__);
  if (!auth_opts->permit_agent_forwarding_flag ||
      !options.allow_agent_forwarding ||
      options.disable_forwarding) {
    debug_f("agent forwarding disabled");
    return 0;
  }
  if (called)
    return 0;

  called = 1;
  return auth_input_request_forwarding(ssh, s->pw, agent_new);
}

int
session_input_channel_req(struct ssh *ssh, Channel *c, const char *rtype)
{
  int success = 0;
  Session *s;

  if ((s = session_by_channel(c->self)) == NULL) {
    logit_f("no session %d req %.100s", c->self, rtype);
    return 0;
  }
  debug_f("session %d req %s", s->self, rtype);

  /*
   * a session is in LARVAL state until a shell, a command
   * or a subsystem is executed
   */
  if (c->type == SSH_CHANNEL_LARVAL) {
    if (strcmp(rtype, "shell") == 0) {
      success = session_shell_req(ssh, s);
    } else if (strcmp(rtype, "exec") == 0) {
      success = session_exec_req(ssh, s);
    } else if (strcmp(rtype, "pty-req") == 0) {
      success = session_pty_req(ssh, s);
    } else if (strcmp(rtype, "x11-req") == 0) {
      success = session_x11_req(ssh, s);
    } else if (strcmp(rtype, "auth-agent-req@openssh.com") == 0) {
      success = session_auth_agent_req(ssh, s, 0);
    } else if (strcmp(rtype, "agent-req") == 0) {
      success = session_auth_agent_req(ssh, s, 1);
    } else if (strcmp(rtype, "subsystem") == 0) {
      success = session_subsystem_req(ssh, s);
    } else if (strcmp(rtype, "env") == 0) {
      success = session_env_req(ssh, s);
    }
  }
  if (strcmp(rtype, "window-change") == 0) {
    success = session_window_change_req(ssh, s);
  } else if (strcmp(rtype, "break") == 0) {
    success = session_break_req(ssh, s);
  } else if (strcmp(rtype, "signal") == 0) {
    success = session_signal_req(ssh, s);
  }

  return success;
}

void
session_set_fds(struct ssh *ssh, Session *s,
    int fdin, int fdout, int fderr, int ignore_fderr, int is_tty)
{
  /*
   * now that have a child and a pipe to the child,
   * we can activate our channel and register the fd's
   */
  if (s->chanid == -1)
    fatal("no channel for session %d", s->self);
  channel_set_fds(ssh, s->chanid,
      fdout, fdin, fderr,
      ignore_fderr ? CHAN_EXTENDED_IGNORE : CHAN_EXTENDED_READ,
      1, is_tty, CHAN_SES_WINDOW_DEFAULT);
}

/*
 * Function to perform pty cleanup. Also called if we get aborted abnormally
 * (e.g., due to a dropped connection).
 */
void
session_pty_cleanup2(Session *s)
{
  if (s == NULL) {
    error_f("no session");
    return;
  }
  if (s->ttyfd == -1)
    return;

  debug_f("session %d release %s", s->self, s->tty);

  /* Record that the user has logged out. */
  if (s->pid != 0)
    record_logout(s->pid, s->tty, s->pw->pw_name);

  /* Release the pseudo-tty. */
  if (getuid() == 0)
    pty_release(s->tty);

  /*
   * Close the server side of the socket pairs.  We must do this after
   * the pty cleanup, so that another process doesn't get this pty
   * while we're still cleaning up.
   */
  if (s->ptymaster != -1 && close(s->ptymaster) == -1)
    error("close(s->ptymaster/%d): %s",
        s->ptymaster, strerror(errno));

  /* unlink pty from session */
  s->ttyfd = -1;
}

void
session_pty_cleanup(Session *s)
{
  mm_session_pty_cleanup2(s);
}

static char *
sig2name(int sig)
{
#define SSH_SIG(x) if (sig == SIG ## x) return #x
  SSH_SIG(ABRT);
  SSH_SIG(ALRM);
  SSH_SIG(FPE);
  SSH_SIG(HUP);
  SSH_SIG(ILL);
  SSH_SIG(INT);
  SSH_SIG(KILL);
  SSH_SIG(PIPE);
  SSH_SIG(QUIT);
  SSH_SIG(SEGV);
  SSH_SIG(TERM);
  SSH_SIG(USR1);
  SSH_SIG(USR2);
#undef  SSH_SIG
  return "SIG@openssh.com";
}

static void
session_close_x11(struct ssh *ssh, int id)
{
  Channel *c;

  if ((c = channel_by_id(ssh, id)) == NULL) {
    debug_f("x11 channel %d missing", id);
  } else {
    /* Detach X11 listener */
    debug_f("detach x11 channel %d", id);
    channel_cancel_cleanup(ssh, id);
    if (c->ostate != CHAN_OUTPUT_CLOSED)
      chan_mark_dead(ssh, c);
  }
}

static void
session_close_single_x11(struct ssh *ssh, int id, int force, void *arg)
{
  Session *s;
  u_int i;

  debug3_f("channel %d", id);
  channel_cancel_cleanup(ssh, id);
  if ((s = session_by_x11_channel(id)) == NULL)
    fatal_f("no x11 channel %d", id);
  for (i = 0; s->x11_chanids[i] != -1; i++) {
    debug_f("session %d: closing channel %d",
        s->self, s->x11_chanids[i]);
    /*
     * The channel "id" is already closing, but make sure we
     * close all of its siblings.
     */
    if (s->x11_chanids[i] != id)
      session_close_x11(ssh, s->x11_chanids[i]);
  }
  free(s->x11_chanids);
  s->x11_chanids = NULL;
  free(s->display);
  s->display = NULL;
  free(s->auth_proto);
  s->auth_proto = NULL;
  free(s->auth_data);
  s->auth_data = NULL;
  free(s->auth_display);
  s->auth_display = NULL;
}

static void
session_exit_message(struct ssh *ssh, Session *s, int status)
{
  Channel *c;
  int r;
  char *note = NULL;

  if ((c = channel_lookup(ssh, s->chanid)) == NULL)
    fatal_f("session %d: no channel %d", s->self, s->chanid);

  if (WIFEXITED(status)) {
    channel_request_start(ssh, s->chanid, "exit-status", 0);
    if ((r = sshpkt_put_u32(ssh, WEXITSTATUS(status))) != 0 ||
        (r = sshpkt_send(ssh)) != 0)
      sshpkt_fatal(ssh, r, "%s: exit reply", __func__);
    xasprintf(&note, "exit %d", WEXITSTATUS(status));
  } else if (WIFSIGNALED(status)) {
    channel_request_start(ssh, s->chanid, "exit-signal", 0);
#ifndef WCOREDUMP
# define WCOREDUMP(x) (0)
#endif
    if ((r = sshpkt_put_cstring(ssh, sig2name(WTERMSIG(status)))) != 0 ||
        (r = sshpkt_put_u8(ssh, WCOREDUMP(status)? 1 : 0)) != 0 ||
        (r = sshpkt_put_cstring(ssh, "")) != 0 ||
        (r = sshpkt_put_cstring(ssh, "")) != 0 ||
        (r = sshpkt_send(ssh)) != 0)
      sshpkt_fatal(ssh, r, "%s: exit reply", __func__);
    xasprintf(&note, "signal %d%s", WTERMSIG(status),
        WCOREDUMP(status) ? " core dumped" : "");
  } else {
    /* Some weird exit cause.  Just exit. */
    ssh_packet_disconnect(ssh, "wait returned status %04x.",
        status);
  }

  debug_f("session %d channel %d pid %ld %s", s->self, s->chanid,
      (long)s->pid, note == NULL ? "UNKNOWN" : note);
  free(note);

  /* disconnect channel */
  debug_f("release channel %d", s->chanid);

  /*
   * Adjust cleanup callback attachment to send close messages when
   * the channel gets EOF. The session will be then be closed
   * by session_close_by_channel when the child sessions close their fds.
   */
  channel_register_cleanup(ssh, c->self, session_close_by_channel, 1);

  /*
   * emulate a write failure with 'chan_write_failed', nobody will be
   * interested in data we write.
   * Note that we must not call 'chan_read_failed', since there could
   * be some more data waiting in the pipe.
   */
  if (c->ostate != CHAN_OUTPUT_CLOSED)
    chan_write_failed(ssh, c);
}

void
session_close(struct ssh *ssh, Session *s)
{
  u_int i;

  verbose("Close session: user %s from %.200s port %d id %d",
      s->pw->pw_name,
      ssh_remote_ipaddr(ssh),
      ssh_remote_port(ssh),
      s->self);

  if (s->ttyfd != -1)
    session_pty_cleanup(s);
  free(s->term);
  free(s->display);
  free(s->x11_chanids);
  free(s->auth_display);
  free(s->auth_data);
  free(s->auth_proto);
  free(s->subsys);
  if (s->env != NULL) {
    for (i = 0; i < s->num_env; i++) {
      free(s->env[i].name);
      free(s->env[i].val);
    }
    free(s->env);
  }
  session_proctitle(s);
  session_unused(s->self);
}

void
session_close_by_pid(struct ssh *ssh, pid_t pid, int status)
{
  Session *s = session_by_pid(pid);
  if (s == NULL) {
    debug_f("no session for pid %ld", (long)pid);
    return;
  }
  if (s->chanid != -1)
    session_exit_message(ssh, s, status);
  if (s->ttyfd != -1)
    session_pty_cleanup(s);
  s->pid = 0;
}

/*
 * this is called when a channel dies before
 * the session 'child' itself dies
 */
void
session_close_by_channel(struct ssh *ssh, int id, int force, void *arg)
{
  Session *s = session_by_channel(id);
  u_int i;

  if (s == NULL) {
    debug_f("no session for id %d", id);
    return;
  }
  debug_f("channel %d child %ld", id, (long)s->pid);
  if (s->pid != 0) {
    debug_f("channel %d: has child, ttyfd %d", id, s->ttyfd);
    /*
     * delay detach of session (unless this is a forced close),
     * but release pty, since the fd's to the child are already
     * closed
     */
    if (s->ttyfd != -1)
      session_pty_cleanup(s);
    if (!force)
      return;
  }
  /* detach by removing callback */
  channel_cancel_cleanup(ssh, s->chanid);

  /* Close any X11 listeners associated with this session */
  if (s->x11_chanids != NULL) {
    for (i = 0; s->x11_chanids[i] != -1; i++) {
      session_close_x11(ssh, s->x11_chanids[i]);
      s->x11_chanids[i] = -1;
    }
  }

  s->chanid = -1;
  session_close(ssh, s);
}

void
session_destroy_all(struct ssh *ssh, void (*closefunc)(Session *))
{
  int i;
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];
    if (s->used) {
      if (closefunc != NULL)
        closefunc(s);
      else
        session_close(ssh, s);
    }
  }
}

static char *
session_tty_list(void)
{
  static char buf[1024];
  int i;
  char *cp;

  buf[0] = '\0';
  for (i = 0; i < sessions_nalloc; i++) {
    Session *s = &sessions[i];
    if (s->used && s->ttyfd != -1) {

      if (strncmp(s->tty, "/dev/", 5) != 0) {
        cp = strrchr(s->tty, '/');
        cp = (cp == NULL) ? s->tty : cp + 1;
      } else
        cp = s->tty + 5;

      if (buf[0] != '\0')
        strlcat(buf, ",", sizeof buf);
      strlcat(buf, cp, sizeof buf);
    }
  }
  if (buf[0] == '\0')
    strlcpy(buf, "notty", sizeof buf);
  return buf;
}

void
session_proctitle(Session *s)
{
  if (s->pw == NULL)
    error("no user for session %d", s->self);
  else
    setproctitle("%s@%s", s->pw->pw_name, session_tty_list());
}

int
session_setup_x11fwd(struct ssh *ssh, Session *s)
{
  struct stat st;
  char display[512], auth_display[512];
  char hostname[NI_MAXHOST];
  u_int i;

  if (!auth_opts->permit_x11_forwarding_flag) {
    ssh_packet_send_debug(ssh, "X11 forwarding disabled by key options.");
    return 0;
  }
  if (!options.x11_forwarding || options.disable_forwarding) {
    debug("X11 forwarding disabled in server configuration file.");
    return 0;
  }
  if (options.xauth_location == NULL ||
      (stat(options.xauth_location, &st) == -1)) {
    ssh_packet_send_debug(ssh, "No xauth program; cannot forward X11.");
    return 0;
  }
  if (s->display != NULL) {
    debug("X11 display already set.");
    return 0;
  }
  if (x11_create_display_inet(ssh, options.x11_display_offset,
      options.x11_use_localhost, s->single_connection,
      &s->display_number, &s->x11_chanids) == -1) {
    debug("x11_create_display_inet failed.");
    return 0;
  }
  for (i = 0; s->x11_chanids[i] != -1; i++) {
    channel_register_cleanup(ssh, s->x11_chanids[i],
        session_close_single_x11, 0);
  }

  /* Set up a suitable value for the DISPLAY variable. */
  if (gethostname(hostname, sizeof(hostname)) == -1)
    fatal("gethostname: %.100s", strerror(errno));
  /*
   * auth_display must be used as the displayname when the
   * authorization entry is added with xauth(1).  This will be
   * different than the DISPLAY string for localhost displays.
   */
  if (options.x11_use_localhost) {
    snprintf(display, sizeof display, "localhost:%u.%u",
        s->display_number, s->screen);
    snprintf(auth_display, sizeof auth_display, "unix:%u.%u",
        s->display_number, s->screen);
    s->display = xstrdup(display);
    s->auth_display = xstrdup(auth_display);
  } else {
#ifdef IPADDR_IN_DISPLAY
    struct hostent *he;
    struct in_addr my_addr;

    he = gethostbyname(hostname);
    if (he == NULL) {
      error("Can't get IP address for X11 DISPLAY.");
      ssh_packet_send_debug(ssh, "Can't get IP address for X11 DISPLAY.");
      return 0;
    }
    memcpy(&my_addr, he->h_addr_list[0], sizeof(struct in_addr));
    snprintf(display, sizeof display, "%.50s:%u.%u", inet_ntoa(my_addr),
        s->display_number, s->screen);
#else
    snprintf(display, sizeof display, "%.400s:%u.%u", hostname,
        s->display_number, s->screen);
#endif
    s->display = xstrdup(display);
    s->auth_display = xstrdup(display);
  }

  return 1;
}

static void
do_authenticated2(struct ssh *ssh, Authctxt *authctxt)
{
  server_loop2(ssh, authctxt);
}

void
do_cleanup(struct ssh *ssh, Authctxt *authctxt)
{
  static int called = 0;

  debug("do_cleanup");

  /* no cleanup if we're in the child for login shell */
  if (is_child)
    return;

  /* avoid double cleanup */
  if (called)
    return;
  called = 1;

  if (authctxt == NULL)
    return;

#ifdef USE_PAM
  if (options.use_pam) {
    sshpam_cleanup();
    sshpam_thread_cleanup();
  }
#endif

  if (!authctxt->authenticated)
    return;

#ifdef KRB5
  if (options.kerberos_ticket_cleanup &&
      authctxt->krb5_ctx)
    krb5_cleanup_proc(authctxt);
#endif

#ifdef GSSAPI
  if (options.gss_cleanup_creds)
    ssh_gssapi_cleanup_creds();
#endif

  /* remove agent socket */
  auth_sock_cleanup_proc(authctxt->pw);

  /* remove userauth info */
  if (auth_info_file != NULL) {
    temporarily_use_uid(authctxt->pw);
    unlink(auth_info_file);
    restore_uid();
    free(auth_info_file);
    auth_info_file = NULL;
  }

  /*
   * Cleanup ptys/utmp only if privsep is disabled,
   * or if running in monitor.
   */
  if (mm_is_monitor())
    session_destroy_all(ssh, session_pty_cleanup2);
}

/* Return a name for the remote host that fits inside utmp_size */

const char *
session_get_remote_name_or_ip(struct ssh *ssh, u_int utmp_size, int use_dns)
{
  const char *remote = "";

  if (utmp_size > 0)
    remote = auth_get_canonical_hostname(ssh, use_dns);
  if (utmp_size == 0 || strlen(remote) > utmp_size)
    remote = ssh_remote_ipaddr(ssh);
  return remote;
}


Coverage Report

Created: 2026-10-13 06:57