/src/openssh/ssh-agent.c

Source
/* $OpenBSD: ssh-agent.c,v 1.331 2026/08/07 05:18:05 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * The authentication agent program.
 *
 * 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".
 *
 * 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/time.h>
#include <sys/queue.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/wait.h>

#ifdef WITH_OPENSSL
#include <openssl/evp.h>
#include "openbsd-compat/openssl-compat.h"
#endif

#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <poll.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <limits.h>
#include <time.h>
#include <unistd.h>
#include <util.h>

#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "authfd.h"
#include "log.h"
#include "misc.h"
#include "digest.h"
#include "ssherr.h"
#include "match.h"
#include "msg.h"
#include "pathnames.h"
#include "ssh-pkcs11.h"
#include "sk-api.h"
#include "myproposal.h"
#include "version.h"

#ifndef DEFAULT_ALLOWED_PROVIDERS
# define DEFAULT_ALLOWED_PROVIDERS "/usr/lib*/*,/usr/local/lib*/*"
#endif
#ifndef DEFAULT_WEBSAFE_ALLOWLIST
# define DEFAULT_WEBSAFE_ALLOWLIST "ssh:*"
#endif

/* Maximum accepted message length */
#define AGENT_MAX_LEN   (256*1024)
/* Maximum bytes to read from client socket */
#define AGENT_RBUF_LEN    (4096)
/* Maximum number of recorded session IDs/hostkeys per connection */
#define AGENT_MAX_SESSION_IDS   16
/* Maximum size of session ID */
#define AGENT_MAX_SID_LEN   128
/* Maximum number of destination constraints to accept on a key */
#define AGENT_MAX_DEST_CONSTRAINTS  1024
/* Maximum number of associated certificate constraints to accept on a key */
#define AGENT_MAX_EXT_CERTS   1024
/* Max length of username constraint */
#define AGENT_USER_CONSTRAINT_MAX_LEN 256

/* XXX store hostkey_sid in a refcounted tree */

typedef enum {
  AUTH_UNUSED = 0,
  AUTH_SOCKET = 1,
  AUTH_CONNECTION = 2,
} sock_type;

struct hostkey_sid {
  struct sshkey *key;
  struct sshbuf *sid;
  int forwarded;
};

typedef struct socket_entry {
  int fd;
  sock_type type;
  struct sshbuf *input;
  struct sshbuf *output;
  struct sshbuf *request;
  size_t nsession_ids;
  struct hostkey_sid *session_ids;
  int session_bind_attempted;
} SocketEntry;

u_int sockets_alloc = 0;
SocketEntry *sockets = NULL;

typedef struct identity {
  TAILQ_ENTRY(identity) next;
  struct sshkey *key;
  char *comment;
  char *provider;
  time_t death;
  u_int confirm;
  char *sk_provider;
  struct dest_constraint *dest_constraints;
  size_t ndest_constraints;
} Identity;

struct idtable {
  int nentries;
  TAILQ_HEAD(idqueue, identity) idlist;
};

/* private key table */
struct idtable *idtab;

int max_fd = 0;

/* pid of shell == parent of agent */
pid_t parent_pid = -1;
time_t parent_alive_interval = 0;

static sig_atomic_t signalled_exit;
static sig_atomic_t signalled_keydrop;

/* pid of process for which cleanup_socket is applicable */
pid_t cleanup_pid = 0;

/* pathname and directory for AUTH_SOCKET */
static char *socket_name;
static char socket_dir[PATH_MAX];

/* Pattern-list of allowed PKCS#11/Security key paths */
static char *allowed_providers;

/*
 * Allows PKCS11 providers or SK keys that use non-internal providers to
 * be added over a remote connection (identified by session-bind@openssh.com).
 */
static int remote_add_provider;

/* locking */
#define LOCK_SIZE 32
#define LOCK_SALT_SIZE  16
#define LOCK_ROUNDS 1
int locked = 0;
u_char lock_pwhash[LOCK_SIZE];
u_char lock_salt[LOCK_SALT_SIZE];

extern char *__progname;

/* Default lifetime in seconds (0 == forever) */
static int lifetime = 0;

static int fingerprint_hash = SSH_FP_HASH_DEFAULT;

/* Refuse signing of non-SSH messages for web-origin FIDO keys */
static int restrict_websafe = 1;
static char *websafe_allowlist;

static void
close_socket(SocketEntry *e)
{
  size_t i;

  close(e->fd);
  sshbuf_free(e->input);
  sshbuf_free(e->output);
  sshbuf_free(e->request);
  for (i = 0; i < e->nsession_ids; i++) {
    sshkey_free(e->session_ids[i].key);
    sshbuf_free(e->session_ids[i].sid);
  }
  free(e->session_ids);
  memset(e, '\0', sizeof(*e));
  e->fd = -1;
  e->type = AUTH_UNUSED;
}

static void
idtab_init(void)
{
  idtab = xcalloc(1, sizeof(*idtab));
  TAILQ_INIT(&idtab->idlist);
  idtab->nentries = 0;
}

static void
free_dest_constraint_hop(struct dest_constraint_hop *dch)
{
  u_int i;

  if (dch == NULL)
    return;
  free(dch->user);
  free(dch->hostname);
  for (i = 0; i < dch->nkeys; i++)
    sshkey_free(dch->keys[i]);
  free(dch->keys);
  free(dch->key_is_ca);
}

static void
free_dest_constraints(struct dest_constraint *dcs, size_t ndcs)
{
  size_t i;

  for (i = 0; i < ndcs; i++) {
    free_dest_constraint_hop(&dcs[i].from);
    free_dest_constraint_hop(&dcs[i].to);
  }
  free(dcs);
}

#ifdef ENABLE_PKCS11
static void
dup_dest_constraint_hop(const struct dest_constraint_hop *dch,
    struct dest_constraint_hop *out)
{
  u_int i;
  int r;

  out->user = dch->user == NULL ? NULL : xstrdup(dch->user);
  out->hostname = dch->hostname == NULL ? NULL : xstrdup(dch->hostname);
  out->is_ca = dch->is_ca;
  out->nkeys = dch->nkeys;
  out->keys = out->nkeys == 0 ? NULL :
      xcalloc(out->nkeys, sizeof(*out->keys));
  out->key_is_ca = out->nkeys == 0 ? NULL :
      xcalloc(out->nkeys, sizeof(*out->key_is_ca));
  for (i = 0; i < dch->nkeys; i++) {
    if (dch->keys[i] != NULL &&
        (r = sshkey_from_private(dch->keys[i],
        &(out->keys[i]))) != 0)
      fatal_fr(r, "copy key");
    out->key_is_ca[i] = dch->key_is_ca[i];
  }
}

static struct dest_constraint *
dup_dest_constraints(const struct dest_constraint *dcs, size_t ndcs)
{
  size_t i;
  struct dest_constraint *ret;

  if (ndcs == 0)
    return NULL;
  ret = xcalloc(ndcs, sizeof(*ret));
  for (i = 0; i < ndcs; i++) {
    dup_dest_constraint_hop(&dcs[i].from, &ret[i].from);
    dup_dest_constraint_hop(&dcs[i].to, &ret[i].to);
  }
  return ret;
}
#endif /* ENABLE_PKCS11 */

#ifdef DEBUG_CONSTRAINTS
static void
dump_dest_constraint_hop(const struct dest_constraint_hop *dch)
{
  u_int i;
  char *fp;

  debug_f("user %s hostname %s is_ca %d nkeys %u",
      dch->user == NULL ? "(null)" : dch->user,
      dch->hostname == NULL ? "(null)" : dch->hostname,
      dch->is_ca, dch->nkeys);
  for (i = 0; i < dch->nkeys; i++) {
    fp = NULL;
    if (dch->keys[i] != NULL &&
        (fp = sshkey_fingerprint(dch->keys[i],
        SSH_FP_HASH_DEFAULT, SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    debug_f("key %u/%u: %s%s%s key_is_ca %d", i, dch->nkeys,
        dch->keys[i] == NULL ? "" : sshkey_ssh_name(dch->keys[i]),
        dch->keys[i] == NULL ? "" : " ",
        dch->keys[i] == NULL ? "none" : fp,
        dch->key_is_ca[i]);
    free(fp);
  }
}
#endif /* DEBUG_CONSTRAINTS */

static void
dump_dest_constraints(const char *context,
    const struct dest_constraint *dcs, size_t ndcs)
{
#ifdef DEBUG_CONSTRAINTS
  size_t i;

  debug_f("%s: %zu constraints", context, ndcs);
  for (i = 0; i < ndcs; i++) {
    debug_f("constraint %zu / %zu: from: ", i, ndcs);
    dump_dest_constraint_hop(&dcs[i].from);
    debug_f("constraint %zu / %zu: to: ", i, ndcs);
    dump_dest_constraint_hop(&dcs[i].to);
  }
  debug_f("done for %s", context);
#endif /* DEBUG_CONSTRAINTS */
}

static void
free_identity(Identity *id)
{
  sshkey_free(id->key);
  free(id->provider);
  free(id->comment);
  free(id->sk_provider);
  free_dest_constraints(id->dest_constraints, id->ndest_constraints);
  free(id);
}

/*
 * Match 'key' against the key/CA list in a destination constraint hop
 * Returns 0 on success or -1 otherwise.
 */
static int
match_key_hop(const char *tag, const struct sshkey *key,
    const struct dest_constraint_hop *dch)
{
  const char *reason = NULL;
  const char *hostname = dch->hostname ? dch->hostname : "(ORIGIN)";
  u_int i;
  char *fp;

  if (key == NULL)
    return -1;
  /* XXX logspam */
  if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
      SSH_FP_DEFAULT)) == NULL)
    fatal_f("fingerprint failed");
  debug3_f("%s: entering hostname %s, requested key %s %s, %u keys avail",
      tag, hostname, sshkey_type(key), fp, dch->nkeys);
  free(fp);
  for (i = 0; i < dch->nkeys; i++) {
    if (dch->keys[i] == NULL)
      return -1;
    /* XXX logspam */
    if ((fp = sshkey_fingerprint(dch->keys[i], SSH_FP_HASH_DEFAULT,
        SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    debug3_f("%s: key %u: %s%s %s", tag, i,
        dch->key_is_ca[i] ? "CA " : "",
        sshkey_type(dch->keys[i]), fp);
    free(fp);
    if (!sshkey_is_cert(key)) {
      /* plain key */
      if (dch->key_is_ca[i] ||
          !sshkey_equal(key, dch->keys[i]))
        continue;
      return 0;
    }
    /* certificate */
    if (!dch->key_is_ca[i])
      continue;
    if (key->cert == NULL || key->cert->signature_key == NULL)
      return -1; /* shouldn't happen */
    if (!sshkey_equal(key->cert->signature_key, dch->keys[i]))
      continue;
    if (sshkey_cert_check_host(key, hostname,
        SSH_ALLOWED_CA_SIGALGS, &reason) != 0) {
      debug_f("cert %s / hostname %s rejected: %s",
          key->cert->key_id, hostname, reason);
      continue;
    }
    return 0;
  }
  return -1;
}

/* Check destination constraints on an identity against the hostkey/user */
static int
permitted_by_dest_constraints(const struct sshkey *fromkey,
    const struct sshkey *tokey, Identity *id, const char *user,
    const char **hostnamep)
{
  size_t i;
  struct dest_constraint *d;

  if (hostnamep != NULL)
    *hostnamep = NULL;
  for (i = 0; i < id->ndest_constraints; i++) {
    d = id->dest_constraints + i;
    /* XXX remove logspam */
    debug2_f("constraint %zu %s%s%s (%u keys) > %s%s%s (%u keys)",
        i, d->from.user ? d->from.user : "",
        d->from.user ? "@" : "",
        d->from.hostname ? d->from.hostname : "(ORIGIN)",
        d->from.nkeys,
        d->to.user ? d->to.user : "", d->to.user ? "@" : "",
        d->to.hostname ? d->to.hostname : "(ANY)", d->to.nkeys);

    /* Match 'from' key */
    if (fromkey == NULL) {
      /* We are matching the first hop */
      if (d->from.hostname != NULL || d->from.nkeys != 0)
        continue;
    } else if (match_key_hop("from", fromkey, &d->from) != 0)
      continue;

    /* Match 'to' key */
    if (tokey != NULL && match_key_hop("to", tokey, &d->to) != 0)
      continue;

    /* Match user if specified */
    if (d->to.user != NULL && user != NULL &&
        !match_pattern(user, d->to.user))
      continue;

    /* successfully matched this constraint */
    if (hostnamep != NULL)
      *hostnamep = d->to.hostname;
    debug2_f("allowed for hostname %s",
        d->to.hostname == NULL ? "*" : d->to.hostname);
    return 0;
  }
  /* no match */
  debug2_f("%s identity \"%s\" not permitted for this destination",
      sshkey_type(id->key), id->comment);
  return -1;
}

/*
 * Check whether hostkeys on a SocketEntry and the optionally specified user
 * are permitted by the destination constraints on the Identity.
 * Returns 0 on success or -1 otherwise.
 */
static int
identity_permitted(Identity *id, SocketEntry *e, char *user,
    const char **forward_hostnamep, const char **last_hostnamep)
{
  size_t i;
  const char **hp;
  struct hostkey_sid *hks;
  const struct sshkey *fromkey = NULL;
  const char *test_user;
  char *fp1, *fp2;

  /* XXX remove logspam */
  debug3_f("entering: key %s comment \"%s\", %zu socket bindings, "
      "%zu constraints", sshkey_type(id->key), id->comment,
      e->nsession_ids, id->ndest_constraints);
  if (id->ndest_constraints == 0)
    return 0; /* unconstrained */
  if (e->session_bind_attempted && e->nsession_ids == 0) {
    error_f("previous session bind failed on socket");
    return -1;
  }
  if (e->nsession_ids == 0)
    return 0; /* local use */
  /*
   * Walk through the hops recorded by session_id and try to find a
   * constraint that satisfies each.
   */
  for (i = 0; i < e->nsession_ids; i++) {
    hks = e->session_ids + i;
    if (hks->key == NULL)
      fatal_f("internal error: no bound key");
    /* XXX remove logspam */
    fp1 = fp2 = NULL;
    if (fromkey != NULL &&
        (fp1 = sshkey_fingerprint(fromkey, SSH_FP_HASH_DEFAULT,
        SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    if ((fp2 = sshkey_fingerprint(hks->key, SSH_FP_HASH_DEFAULT,
        SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    debug3_f("socketentry fd=%d, entry %zu %s, "
        "from hostkey %s %s to user %s hostkey %s %s",
        e->fd, i, hks->forwarded ? "FORWARD" : "AUTH",
        fromkey ? sshkey_type(fromkey) : "(ORIGIN)",
        fromkey ? fp1 : "", user ? user : "(ANY)",
        sshkey_type(hks->key), fp2);
    free(fp1);
    free(fp2);
    /*
     * Record the hostnames for the initial forwarding and
     * the final destination.
     */
    hp = NULL;
    if (i == e->nsession_ids - 1)
      hp = last_hostnamep;
    else if (i == 0)
      hp = forward_hostnamep;
    /* Special handling for final recorded binding */
    test_user = NULL;
    if (i == e->nsession_ids - 1) {
      /* Can only check user at final hop */
      test_user = user;
      /*
       * user is only presented for signature requests.
       * If this is the case, make sure last binding is not
       * for a forwarding.
       */
      if (hks->forwarded && user != NULL) {
        error_f("tried to sign on forwarding hop");
        return -1;
      }
    } else if (!hks->forwarded) {
      error_f("tried to forward though signing bind");
      return -1;
    }
    if (permitted_by_dest_constraints(fromkey, hks->key, id,
        test_user, hp) != 0)
      return -1;
    fromkey = hks->key;
  }
  /*
   * Another special case: if the last bound session ID was for a
   * forwarding, and this function is not being called to check a sign
   * request (i.e. no 'user' supplied), then only permit the key if
   * there is a permission that would allow it to be used at another
   * destination. This hides keys that are allowed to be used to
   * authenticate *to* a host but not permitted for *use* beyond it.
   */
  hks = &e->session_ids[e->nsession_ids - 1];
  if (hks->forwarded && user == NULL &&
      permitted_by_dest_constraints(hks->key, NULL, id,
      NULL, NULL) != 0) {
    debug3_f("key permitted at host but not after");
    return -1;
  }

  /* success */
  return 0;
}

static int
socket_is_remote(SocketEntry *e)
{
  return e->session_bind_attempted || (e->nsession_ids != 0);
}

/* return matching private key for given public key */
static Identity *
lookup_identity(struct sshkey *key)
{
  Identity *id;

  TAILQ_FOREACH(id, &idtab->idlist, next) {
    if (sshkey_equal(key, id->key))
      return (id);
  }
  return (NULL);
}

/* Check confirmation of keysign request */
static int
confirm_key(Identity *id, const char *extra)
{
  char *p;
  int ret = -1;

  p = sshkey_fingerprint(id->key, fingerprint_hash, SSH_FP_DEFAULT);
  if (p != NULL &&
      ask_permission("Allow use of key %s?\nKey fingerprint %s.%s%s",
      id->comment, p,
      extra == NULL ? "" : "\n", extra == NULL ? "" : extra))
    ret = 0;
  free(p);

  return (ret);
}

static void
send_status_generic(SocketEntry *e, u_int code)
{
  int r;

  if ((r = sshbuf_put_u32(e->output, 1)) != 0 ||
      (r = sshbuf_put_u8(e->output, code)) != 0)
    fatal_fr(r, "compose");
}

static void
send_status(SocketEntry *e, int success)
{
  send_status_generic(e,
      success ? SSH_AGENT_SUCCESS : SSH_AGENT_FAILURE);
}

/* send list of supported public keys to 'client' */
static void
process_request_identities(SocketEntry *e)
{
  Identity *id;
  struct sshbuf *msg, *keys;
  int r;
  u_int i = 0, nentries = 0;
  char *fp;

  debug2_f("entering");

  if ((msg = sshbuf_new()) == NULL || (keys = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  TAILQ_FOREACH(id, &idtab->idlist, next) {
    if ((fp = sshkey_fingerprint(id->key, SSH_FP_HASH_DEFAULT,
        SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    debug_f("key %u / %u: %s %s", i++, idtab->nentries,
        sshkey_ssh_name(id->key), fp);
    dump_dest_constraints(__func__,
        id->dest_constraints, id->ndest_constraints);
    free(fp);
    /* identity not visible, don't include in response */
    if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
      continue;
    if ((r = sshkey_puts(id->key, keys)) != 0 ||
        (r = sshbuf_put_cstring(keys, id->comment)) != 0) {
      error_fr(r, "compose key/comment");
      continue;
    }
    nentries++;
  }
  debug2_f("replying with %u allowed of %u available keys",
      nentries, idtab->nentries);
  if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
      (r = sshbuf_put_u32(msg, nentries)) != 0 ||
      (r = sshbuf_putb(msg, keys)) != 0)
    fatal_fr(r, "compose");
  if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
    fatal_fr(r, "enqueue");
  sshbuf_free(msg);
  sshbuf_free(keys);
}


static char *
agent_decode_alg(struct sshkey *key, u_int flags)
{
  if (key->type == KEY_RSA) {
    if (flags & SSH_AGENT_RSA_SHA2_256)
      return "rsa-sha2-256";
    else if (flags & SSH_AGENT_RSA_SHA2_512)
      return "rsa-sha2-512";
  } else if (key->type == KEY_RSA_CERT) {
    if (flags & SSH_AGENT_RSA_SHA2_256)
      return "rsa-sha2-256-cert-v01@openssh.com";
    else if (flags & SSH_AGENT_RSA_SHA2_512)
      return "rsa-sha2-512-cert-v01@openssh.com";
  }
  return NULL;
}

/*
 * Attempt to parse the contents of a buffer as a SSH publickey userauth
 * request, checking its contents for consistency and matching the embedded
 * key against the one that is being used for signing.
 * Note: does not modify msg buffer.
 * Optionally extract the username, session ID and/or hostkey from the request.
 */
static int
parse_userauth_request(struct sshbuf *msg, const struct sshkey *expected_key,
    char **userp, struct sshbuf **sess_idp, struct sshkey **hostkeyp)
{
  struct sshbuf *b = NULL, *sess_id = NULL;
  char *user = NULL, *service = NULL, *method = NULL, *pkalg = NULL;
  int r;
  u_char t, sig_follows;
  struct sshkey *mkey = NULL, *hostkey = NULL;

  if (userp != NULL)
    *userp = NULL;
  if (sess_idp != NULL)
    *sess_idp = NULL;
  if (hostkeyp != NULL)
    *hostkeyp = NULL;
  if ((b = sshbuf_fromb(msg)) == NULL)
    fatal_f("sshbuf_fromb");

  /* SSH userauth request */
  if ((r = sshbuf_froms(b, &sess_id)) != 0)
    goto out;
  if (sshbuf_len(sess_id) == 0) {
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  if ((r = sshbuf_get_u8(b, &t)) != 0 || /* SSH2_MSG_USERAUTH_REQUEST */
      (r = sshbuf_get_cstring(b, &user, NULL)) != 0 || /* server user */
      (r = sshbuf_get_cstring(b, &service, NULL)) != 0 || /* service */
      (r = sshbuf_get_cstring(b, &method, NULL)) != 0 || /* method */
      (r = sshbuf_get_u8(b, &sig_follows)) != 0 || /* sig-follows */
      (r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || /* alg */
      (r = sshkey_froms(b, &mkey)) != 0) /* key */
    goto out;
  if (t != SSH2_MSG_USERAUTH_REQUEST ||
      sig_follows != 1 ||
      strcmp(service, "ssh-connection") != 0 ||
      !sshkey_equal(expected_key, mkey) ||
      sshkey_type_from_name(pkalg) != expected_key->type) {
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  if (strcmp(method, "publickey-hostbound-v00@openssh.com") == 0) {
    if ((r = sshkey_froms(b, &hostkey)) != 0)
      goto out;
  } else if (strcmp(method, "publickey") != 0) {
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  if (sshbuf_len(b) != 0) {
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  /* success */
  r = 0;
  debug3_f("well formed userauth");
  if (userp != NULL) {
    *userp = user;
    user = NULL;
  }
  if (sess_idp != NULL) {
    *sess_idp = sess_id;
    sess_id = NULL;
  }
  if (hostkeyp != NULL) {
    *hostkeyp = hostkey;
    hostkey = NULL;
  }
 out:
  sshbuf_free(b);
  sshbuf_free(sess_id);
  free(user);
  free(service);
  free(method);
  free(pkalg);
  sshkey_free(mkey);
  sshkey_free(hostkey);
  return r;
}

/*
 * Attempt to parse the contents of a buffer as a SSHSIG signature request.
 * Note: does not modify buffer.
 */
static int
parse_sshsig_request(struct sshbuf *msg)
{
  int r;
  struct sshbuf *b;

  if ((b = sshbuf_fromb(msg)) == NULL)
    fatal_f("sshbuf_fromb");

  if ((r = sshbuf_cmp(b, 0, "SSHSIG", 6)) != 0 ||
      (r = sshbuf_consume(b, 6)) != 0 ||
      (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* namespace */
      (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0 || /* reserved */
      (r = sshbuf_get_cstring(b, NULL, NULL)) != 0 || /* hashalg */
      (r = sshbuf_get_string_direct(b, NULL, NULL)) != 0) /* H(msg) */
    goto out;
  if (sshbuf_len(b) != 0) {
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  /* success */
  r = 0;
 out:
  sshbuf_free(b);
  return r;
}

/*
 * This function inspects a message to be signed by a FIDO key that has a
 * web-like application string (i.e. one that does not begin with "ssh:".
 * It checks that the message is one of those expected for SSH operations
 * (pubkey userauth, sshsig, CA key signing) to exclude signing challenges
 * for the web.
 */
static int
check_websafe_message_contents(struct sshkey *key, struct sshbuf *data)
{
  if (parse_userauth_request(data, key, NULL, NULL, NULL) == 0) {
    debug_f("signed data matches public key userauth request");
    return 1;
  }
  if (parse_sshsig_request(data) == 0) {
    debug_f("signed data matches SSHSIG signature request");
    return 1;
  }

  /* XXX check CA signature operation */

  error("web-origin key attempting to sign non-SSH message");
  return 0;
}

static int
buf_equal(const struct sshbuf *a, const struct sshbuf *b)
{
  if (sshbuf_ptr(a) == NULL || sshbuf_ptr(b) == NULL)
    return SSH_ERR_INVALID_ARGUMENT;
  if (sshbuf_len(a) != sshbuf_len(b))
    return SSH_ERR_INVALID_FORMAT;
  if (timingsafe_bcmp(sshbuf_ptr(a), sshbuf_ptr(b), sshbuf_len(a)) != 0)
    return SSH_ERR_INVALID_FORMAT;
  return 0;
}

/* ssh2 only */
static void
process_sign_request2(SocketEntry *e)
{
  u_char *signature = NULL;
  size_t slen = 0;
  u_int compat = 0, flags;
  int r, ok = -1, retried = 0;
  char *fp = NULL, *pin = NULL, *prompt = NULL;
  char *user = NULL, *sig_dest = NULL;
  const char *fwd_host = NULL, *dest_host = NULL;
  struct sshbuf *msg = NULL, *data = NULL, *sid = NULL;
  struct sshkey *key = NULL, *hostkey = NULL;
  struct identity *id;
  struct notifier_ctx *notifier = NULL;

  debug_f("entering");

  if ((msg = sshbuf_new()) == NULL || (data = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  if ((r = sshkey_froms(e->request, &key)) != 0 ||
      (r = sshbuf_get_stringb(e->request, data)) != 0 ||
      (r = sshbuf_get_u32(e->request, &flags)) != 0) {
    error_fr(r, "parse");
    goto send;
  }

  if ((id = lookup_identity(key)) == NULL) {
    verbose_f("%s key not found", sshkey_type(key));
    goto send;
  }
  if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
      SSH_FP_DEFAULT)) == NULL)
    fatal_f("fingerprint failed");

  if (id->ndest_constraints != 0) {
    if (e->nsession_ids == 0) {
      logit_f("refusing use of destination-constrained key "
          "to sign on unbound connection");
      goto send;
    }
    if (parse_userauth_request(data, key, &user, &sid,
        &hostkey) != 0) {
      logit_f("refusing use of destination-constrained key "
         "to sign an unidentified signature");
      goto send;
    }
    /* XXX logspam */
    debug_f("user=%s", user);
    if (identity_permitted(id, e, user, &fwd_host, &dest_host) != 0)
      goto send;
    /* XXX display fwd_host/dest_host in askpass UI */
    /*
     * Ensure that the session ID is the most recent one
     * registered on the socket - it should have been bound by
     * ssh immediately before userauth.
     */
    if (buf_equal(sid,
        e->session_ids[e->nsession_ids - 1].sid) != 0) {
      error_f("unexpected session ID (%zu listed) on "
          "signature request for target user %s with "
          "key %s %s", e->nsession_ids, user,
          sshkey_type(id->key), fp);
      goto send;
    }
    /*
     * Ensure that the hostkey embedded in the signature matches
     * the one most recently bound to the socket. An exception is
     * made for the initial forwarding hop.
     */
    if (e->nsession_ids > 1 && hostkey == NULL) {
      error_f("refusing use of destination-constrained key: "
          "no hostkey recorded in signature for forwarded "
          "connection");
      goto send;
    }
    if (hostkey != NULL && !sshkey_equal(hostkey,
        e->session_ids[e->nsession_ids - 1].key)) {
      error_f("refusing use of destination-constrained key: "
          "mismatch between hostkey in request and most "
          "recently bound session");
      goto send;
    }
    xasprintf(&sig_dest, "public key authentication request for "
        "user \"%s\" to listed host", user);
  }
  if (id->confirm && confirm_key(id, sig_dest) != 0) {
    verbose_f("user refused key");
    goto send;
  }
  if (sshkey_is_sk(id->key)) {
    if (restrict_websafe &&
        match_pattern_list(id->key->sk_application,
        websafe_allowlist, 0) != 1 &&
        !check_websafe_message_contents(key, data)) {
      /* error already logged */
      goto send;
    }
    if (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) {
      notifier = notify_start(0,
          "Confirm user presence for key %s %s%s%s",
          sshkey_type(id->key), fp,
          sig_dest == NULL ? "" : "\n",
          sig_dest == NULL ? "" : sig_dest);
    }
  }
 retry_pin:
  if ((r = sshkey_sign(id->key, &signature, &slen,
      sshbuf_ptr(data), sshbuf_len(data), agent_decode_alg(key, flags),
      id->sk_provider, pin, compat)) != 0) {
    debug_fr(r, "sshkey_sign");
    if (pin == NULL && !retried && sshkey_is_sk(id->key) &&
        r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
      notify_complete(notifier, NULL);
      notifier = NULL;
      /* XXX include sig_dest */
      xasprintf(&prompt, "Enter PIN%sfor %s key %s: ",
          (id->key->sk_flags & SSH_SK_USER_PRESENCE_REQD) ?
          " and confirm user presence " : " ",
          sshkey_type(id->key), fp);
      pin = read_passphrase(prompt, RP_USE_ASKPASS);
      retried = 1;
      goto retry_pin;
    }
    error_fr(r, "sshkey_sign");
    goto send;
  }
  /* Success */
  ok = 0;
  debug_f("good signature");
 send:
  notify_complete(notifier, "User presence confirmed");

  if (ok == 0) {
    if ((r = sshbuf_put_u8(msg, SSH2_AGENT_SIGN_RESPONSE)) != 0 ||
        (r = sshbuf_put_string(msg, signature, slen)) != 0)
      fatal_fr(r, "compose");
  } else if ((r = sshbuf_put_u8(msg, SSH_AGENT_FAILURE)) != 0)
    fatal_fr(r, "compose failure");

  if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
    fatal_fr(r, "enqueue");

  sshbuf_free(sid);
  sshbuf_free(data);
  sshbuf_free(msg);
  sshkey_free(key);
  sshkey_free(hostkey);
  free(fp);
  free(signature);
  free(sig_dest);
  free(user);
  free(prompt);
  if (pin != NULL)
    freezero(pin, strlen(pin));
}

/* shared */
static void
process_remove_identity(SocketEntry *e)
{
  int r, success = 0;
  struct sshkey *key = NULL;
  Identity *id;

  debug2_f("entering");
  if ((r = sshkey_froms(e->request, &key)) != 0) {
    error_fr(r, "parse key");
    goto done;
  }
  if ((id = lookup_identity(key)) == NULL) {
    debug_f("key not found");
    goto done;
  }
  /* identity not visible, cannot be removed */
  if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
    goto done; /* error already logged */
  /* We have this key, free it. */
  if (idtab->nentries < 1)
    fatal_f("internal error: nentries %d", idtab->nentries);
  TAILQ_REMOVE(&idtab->idlist, id, next);
  free_identity(id);
  idtab->nentries--;
  success = 1;
 done:
  sshkey_free(key);
  send_status(e, success);
}

static void
remove_all_identities(void)
{
  Identity *id;

  debug2_f("entering");
  /* Loop over all identities and clear the keys. */
  for (id = TAILQ_FIRST(&idtab->idlist); id;
      id = TAILQ_FIRST(&idtab->idlist)) {
    TAILQ_REMOVE(&idtab->idlist, id, next);
    free_identity(id);
  }

  /* Mark that there are no identities. */
  idtab->nentries = 0;
}

static void
process_remove_all_identities(SocketEntry *e)
{
  remove_all_identities();

  /* Send success. */
  send_status(e, 1);
}

/* removes expired keys and returns number of seconds until the next expiry */
static time_t
reaper(void)
{
  time_t deadline = 0, now = monotime();
  Identity *id, *nxt;

  for (id = TAILQ_FIRST(&idtab->idlist); id; id = nxt) {
    nxt = TAILQ_NEXT(id, next);
    if (id->death == 0)
      continue;
    if (now >= id->death) {
      debug("expiring key '%s'", id->comment);
      TAILQ_REMOVE(&idtab->idlist, id, next);
      free_identity(id);
      idtab->nentries--;
    } else
      deadline = (deadline == 0) ? id->death :
          MINIMUM(deadline, id->death);
  }
  if (deadline == 0 || deadline <= now)
    return 0;
  else
    return (deadline - now);
}

static int
parse_dest_constraint_hop(struct sshbuf *b, struct dest_constraint_hop *dch)
{
  u_char key_is_ca;
  size_t elen = 0, userlen = 0;
  int r;
  struct sshkey *k = NULL;
  char *fp;

  memset(dch, '\0', sizeof(*dch));
  if ((r = sshbuf_get_cstring(b, &dch->user, &userlen)) != 0 ||
      (r = sshbuf_get_cstring(b, &dch->hostname, NULL)) != 0 ||
      (r = sshbuf_get_string_direct(b, NULL, &elen)) != 0) {
    error_fr(r, "parse");
    goto out;
  }
  if (elen != 0) {
    error_f("unsupported extensions (len %zu)", elen);
    r = SSH_ERR_FEATURE_UNSUPPORTED;
    goto out;
  }
  if (*dch->hostname == '\0') {
    free(dch->hostname);
    dch->hostname = NULL;
  }
  if (*dch->user == '\0') {
    free(dch->user);
    dch->user = NULL;
  } else if (userlen > AGENT_USER_CONSTRAINT_MAX_LEN) {
    error_f("user match pattern too long");
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  while (sshbuf_len(b) != 0) {
    dch->keys = xrecallocarray(dch->keys, dch->nkeys,
        dch->nkeys + 1, sizeof(*dch->keys));
    dch->key_is_ca = xrecallocarray(dch->key_is_ca, dch->nkeys,
        dch->nkeys + 1, sizeof(*dch->key_is_ca));
    if ((r = sshkey_froms(b, &k)) != 0 ||
        (r = sshbuf_get_u8(b, &key_is_ca)) != 0)
      goto out;
    if ((fp = sshkey_fingerprint(k, SSH_FP_HASH_DEFAULT,
        SSH_FP_DEFAULT)) == NULL)
      fatal_f("fingerprint failed");
    debug3_f("%s%s%s: adding %skey %s %s",
        dch->user == NULL ? "" : dch->user,
        dch->user == NULL ? "" : "@",
        dch->hostname, key_is_ca ? "CA " : "", sshkey_type(k), fp);
    free(fp);
    dch->keys[dch->nkeys] = k;
    dch->key_is_ca[dch->nkeys] = key_is_ca != 0;
    dch->nkeys++;
    k = NULL; /* transferred */
  }
  /* success */
  r = 0;
 out:
  sshkey_free(k);
  return r;
}

static int
parse_dest_constraint(struct sshbuf *m, struct dest_constraint *dc)
{
  struct sshbuf *b = NULL, *frombuf = NULL, *tobuf = NULL;
  int r;
  size_t elen = 0;

  debug3_f("entering");

  memset(dc, '\0', sizeof(*dc));
  if ((r = sshbuf_froms(m, &b)) != 0 ||
      (r = sshbuf_froms(b, &frombuf)) != 0 ||
      (r = sshbuf_froms(b, &tobuf)) != 0 ||
      (r = sshbuf_get_string_direct(b, NULL, &elen)) != 0) {
    error_fr(r, "parse");
    goto out;
  }
  if ((r = parse_dest_constraint_hop(frombuf, &dc->from)) != 0 ||
      (r = parse_dest_constraint_hop(tobuf, &dc->to)) != 0)
    goto out; /* already logged */
  if (elen != 0) {
    error_f("unsupported extensions (len %zu)", elen);
    r = SSH_ERR_FEATURE_UNSUPPORTED;
    goto out;
  }
  debug2_f("parsed %s (%u keys) > %s%s%s (%u keys)",
      dc->from.hostname ? dc->from.hostname : "(ORIGIN)", dc->from.nkeys,
      dc->to.user ? dc->to.user : "", dc->to.user ? "@" : "",
      dc->to.hostname ? dc->to.hostname : "(ANY)", dc->to.nkeys);
  /* check consistency */
  if ((dc->from.hostname == NULL) != (dc->from.nkeys == 0) ||
      dc->from.user != NULL) {
    error_f("inconsistent \"from\" specification");
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  if (dc->to.hostname == NULL || dc->to.nkeys == 0) {
    error_f("incomplete \"to\" specification");
    r = SSH_ERR_INVALID_FORMAT;
    goto out;
  }
  /* success */
  r = 0;
 out:
  sshbuf_free(b);
  sshbuf_free(frombuf);
  sshbuf_free(tobuf);
  return r;
}

static int
parse_key_constraint_extension(struct sshbuf *m, char **sk_providerp,
    struct dest_constraint **dcsp, size_t *ndcsp, int *cert_onlyp,
    struct sshkey ***certs, size_t *ncerts)
{
  char *ext_name = NULL;
  int r;
  struct sshbuf *b = NULL;
  u_char v;
  struct sshkey *k;

  if ((r = sshbuf_get_cstring(m, &ext_name, NULL)) != 0) {
    error_fr(r, "parse constraint extension");
    goto out;
  }
  debug_f("constraint ext %s", ext_name);
  if (strcmp(ext_name, "sk-provider@openssh.com") == 0) {
    if (sk_providerp == NULL) {
      error_f("%s not valid here", ext_name);
      r = SSH_ERR_INVALID_FORMAT;
      goto out;
    }
    if (*sk_providerp != NULL) {
      error_f("%s already set", ext_name);
      r = SSH_ERR_INVALID_FORMAT;
      goto out;
    }
    if ((r = sshbuf_get_cstring(m, sk_providerp, NULL)) != 0) {
      error_fr(r, "parse %s", ext_name);
      goto out;
    }
  } else if (strcmp(ext_name,
      "restrict-destination-v00@openssh.com") == 0) {
    if (*dcsp != NULL) {
      error_f("%s already set", ext_name);
      r = SSH_ERR_INVALID_FORMAT;
      goto out;
    }
    if ((r = sshbuf_froms(m, &b)) != 0) {
      error_fr(r, "parse %s outer", ext_name);
      goto out;
    }
    while (sshbuf_len(b) != 0) {
      if (*ndcsp >= AGENT_MAX_DEST_CONSTRAINTS) {
        error_f("too many %s constraints", ext_name);
        r = SSH_ERR_INVALID_FORMAT;
        goto out;
      }
      *dcsp = xrecallocarray(*dcsp, *ndcsp, *ndcsp + 1,
          sizeof(**dcsp));
      if ((r = parse_dest_constraint(b,
          *dcsp + (*ndcsp)++)) != 0)
        goto out; /* error already logged */
    }
  } else if (strcmp(ext_name,
      "associated-certs-v00@openssh.com") == 0) {
    if (certs == NULL || ncerts == NULL || cert_onlyp == NULL) {
      error_f("%s not valid here", ext_name);
      r = SSH_ERR_INVALID_FORMAT;
      goto out;
    }
    if (*certs != NULL) {
      error_f("%s already set", ext_name);
      r = SSH_ERR_INVALID_FORMAT;
      goto out;
    }
    if ((r = sshbuf_get_u8(m, &v)) != 0 ||
        (r = sshbuf_froms(m, &b)) != 0) {
      error_fr(r, "parse %s", ext_name);
      goto out;
    }
    *cert_onlyp = v != 0;
    while (sshbuf_len(b) != 0) {
      if (*ncerts >= AGENT_MAX_EXT_CERTS) {
        error_f("too many %s constraints", ext_name);
        r = SSH_ERR_INVALID_FORMAT;
        goto out;
      }
      *certs = xrecallocarray(*certs, *ncerts, *ncerts + 1,
          sizeof(**certs));
      if ((r = sshkey_froms(b, &k)) != 0) {
        error_fr(r, "parse key");
        goto out;
      }
      (*certs)[(*ncerts)++] = k;
    }
  } else {
    error_f("unsupported constraint \"%s\"", ext_name);
    r = SSH_ERR_FEATURE_UNSUPPORTED;
    goto out;
  }
  /* success */
  r = 0;
 out:
  free(ext_name);
  sshbuf_free(b);
  return r;
}

static int
parse_key_constraints(struct sshbuf *m, struct sshkey *k, time_t *deathp,
    u_int *secondsp, int *confirmp, char **sk_providerp,
    struct dest_constraint **dcsp, size_t *ndcsp,
    int *cert_onlyp, size_t *ncerts, struct sshkey ***certs)
{
  u_char ctype;
  int r;
  u_int seconds;

  while (sshbuf_len(m)) {
    if ((r = sshbuf_get_u8(m, &ctype)) != 0) {
      error_fr(r, "parse constraint type");
      goto out;
    }
    switch (ctype) {
    case SSH_AGENT_CONSTRAIN_LIFETIME:
      if (*deathp != 0) {
        error_f("lifetime already set");
        r = SSH_ERR_INVALID_FORMAT;
        goto out;
      }
      if ((r = sshbuf_get_u32(m, &seconds)) != 0) {
        error_fr(r, "parse lifetime constraint");
        goto out;
      }
      *deathp = monotime() + seconds;
      *secondsp = seconds;
      break;
    case SSH_AGENT_CONSTRAIN_CONFIRM:
      if (*confirmp != 0) {
        error_f("confirm already set");
        r = SSH_ERR_INVALID_FORMAT;
        goto out;
      }
      *confirmp = 1;
      break;
    case SSH_AGENT_CONSTRAIN_EXTENSION:
      if ((r = parse_key_constraint_extension(m,
          sk_providerp, dcsp, ndcsp,
          cert_onlyp, certs, ncerts)) != 0)
        goto out; /* error already logged */
      break;
    default:
      error_f("Unknown constraint %d", ctype);
      r = SSH_ERR_FEATURE_UNSUPPORTED;
      goto out;
    }
  }
  /* success */
  r = 0;
 out:
  return r;
}

static void
process_add_identity(SocketEntry *e)
{
  Identity *id;
  int success = 0, confirm = 0;
  char *fp, *comment = NULL, *sk_provider = NULL;
  char canonical_provider[PATH_MAX];
  time_t death = 0;
  u_int seconds = 0;
  struct dest_constraint *dest_constraints = NULL;
  size_t ndest_constraints = 0;
  struct sshkey *k = NULL;
  int r = SSH_ERR_INTERNAL_ERROR;

  debug2_f("entering");
  if ((r = sshkey_private_deserialize(e->request, &k)) != 0 ||
      k == NULL ||
      (r = sshbuf_get_cstring(e->request, &comment, NULL)) != 0) {
    error_fr(r, "parse");
    goto out;
  }
  if (parse_key_constraints(e->request, k, &death, &seconds, &confirm,
      &sk_provider, &dest_constraints, &ndest_constraints,
      NULL, NULL, NULL) != 0) {
    error_f("failed to parse constraints");
    sshbuf_reset(e->request);
    goto out;
  }
  dump_dest_constraints(__func__, dest_constraints, ndest_constraints);

  if (sk_provider != NULL) {
    if (!sshkey_is_sk(k)) {
      error("Cannot add provider: %s is not an "
          "authenticator-hosted key", sshkey_type(k));
      goto out;
    }
    if (strcasecmp(sk_provider, "internal") == 0) {
      debug_f("internal provider");
    } else {
      if (socket_is_remote(e) && !remote_add_provider) {
        verbose("failed add of SK provider \"%.100s\": "
            "remote addition of providers is disabled",
            sk_provider);
        goto out;
      }
      if (realpath(sk_provider, canonical_provider) == NULL) {
        verbose("failed provider \"%.100s\": "
            "realpath: %s", sk_provider,
            strerror(errno));
        goto out;
      }
      free(sk_provider);
      sk_provider = xstrdup(canonical_provider);
      if (match_pattern_list(sk_provider,
          allowed_providers, 0) != 1) {
        error("Refusing add key: "
            "provider %s not allowed", sk_provider);
        goto out;
      }
    }
  }
  if ((r = sshkey_shield_private(k)) != 0) {
    error_fr(r, "shield private");
    goto out;
  }
  if (lifetime && !death)
    death = monotime() + lifetime;
  if ((id = lookup_identity(k)) == NULL) {
    id = xcalloc(1, sizeof(Identity));
    TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
    /* Increment the number of identities. */
    idtab->nentries++;
  } else {
    /* identity not visible, do not update */
    if (identity_permitted(id, e, NULL, NULL, NULL) != 0)
      goto out; /* error already logged */
    /* key state might have been updated */
    sshkey_free(id->key);
    free(id->comment);
    free(id->sk_provider);
    free_dest_constraints(id->dest_constraints,
        id->ndest_constraints);
  }
  /* success */
  id->key = k;
  id->comment = comment;
  id->death = death;
  id->confirm = confirm;
  id->sk_provider = sk_provider;
  id->dest_constraints = dest_constraints;
  id->ndest_constraints = ndest_constraints;

  if ((fp = sshkey_fingerprint(k, SSH_FP_HASH_DEFAULT,
      SSH_FP_DEFAULT)) == NULL)
    fatal_f("sshkey_fingerprint failed");
  debug_f("add %s %s \"%.100s\" (life: %u) (confirm: %u) "
      "(provider: %s) (destination constraints: %zu)",
      sshkey_ssh_name(k), fp, comment, seconds, confirm,
      sk_provider == NULL ? "none" : sk_provider, ndest_constraints);
  free(fp);
  /* transferred */
  k = NULL;
  comment = NULL;
  sk_provider = NULL;
  dest_constraints = NULL;
  ndest_constraints = 0;
  success = 1;
 out:
  free(sk_provider);
  free(comment);
  sshkey_free(k);
  free_dest_constraints(dest_constraints, ndest_constraints);
  send_status(e, success);
}

/* XXX todo: encrypt sensitive data with passphrase */
static void
process_lock_agent(SocketEntry *e, int lock)
{
  int r, success = 0, delay;
  char *passwd;
  u_char passwdhash[LOCK_SIZE];
  static u_int fail_count = 0;
  size_t pwlen;

  debug2_f("entering");
  /*
   * This is deliberately fatal: the user has requested that we lock,
   * but we can't parse their request properly. The only safe thing to
   * do is abort.
   */
  if ((r = sshbuf_get_cstring(e->request, &passwd, &pwlen)) != 0)
    fatal_fr(r, "parse");
  if (pwlen == 0) {
    debug("empty password not supported");
  } else if (locked && !lock) {
    if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
        passwdhash, sizeof(passwdhash), LOCK_ROUNDS) < 0)
      fatal("bcrypt_pbkdf");
    if (timingsafe_bcmp(passwdhash, lock_pwhash, LOCK_SIZE) == 0) {
      debug("agent unlocked");
      locked = 0;
      fail_count = 0;
      explicit_bzero(lock_pwhash, sizeof(lock_pwhash));
      success = 1;
    } else {
      /* delay in 0.1s increments up to 10s */
      if (fail_count < 100)
        fail_count++;
      delay = 100000 * fail_count;
      debug("unlock failed, delaying %0.1lf seconds",
          (double)delay/1000000);
      // usleep(delay);
    }
    explicit_bzero(passwdhash, sizeof(passwdhash));
  } else if (!locked && lock) {
    debug("agent locked");
    locked = 1;
    arc4random_buf(lock_salt, sizeof(lock_salt));
    if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
        lock_pwhash, sizeof(lock_pwhash), LOCK_ROUNDS) < 0)
      fatal("bcrypt_pbkdf");
    success = 1;
  }
  freezero(passwd, pwlen);
  send_status(e, success);
}

static void
no_identities(SocketEntry *e)
{
  struct sshbuf *msg;
  int r;

  if ((msg = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  if ((r = sshbuf_put_u8(msg, SSH2_AGENT_IDENTITIES_ANSWER)) != 0 ||
      (r = sshbuf_put_u32(msg, 0)) != 0 ||
      (r = sshbuf_put_stringb(e->output, msg)) != 0)
    fatal_fr(r, "compose");
  sshbuf_free(msg);
}

#ifdef ENABLE_PKCS11
/* Add an identity to idlist; takes ownership of 'key' and 'comment' */
static void
add_p11_identity(struct sshkey *key, char *comment, const char *provider,
    time_t death, u_int confirm, struct dest_constraint *dest_constraints,
    size_t ndest_constraints)
{
  Identity *id;

  if (lookup_identity(key) != NULL) {
    sshkey_free(key);
    free(comment);
    return;
  }
  id = xcalloc(1, sizeof(Identity));
  id->key = key;
  id->comment = comment;
  id->provider = xstrdup(provider);
  id->death = death;
  id->confirm = confirm;
  id->dest_constraints = dup_dest_constraints(dest_constraints,
      ndest_constraints);
  id->ndest_constraints = ndest_constraints;
  TAILQ_INSERT_TAIL(&idtab->idlist, id, next);
  idtab->nentries++;
}

static void
process_add_smartcard_key(SocketEntry *e)
{
  char *provider = NULL, *pin = NULL, canonical_provider[PATH_MAX];
  char **comments = NULL;
  int r, i, count = 0, success = 0, confirm = 0;
  u_int seconds = 0;
  time_t death = 0;
  struct sshkey **keys = NULL, *k;
  struct dest_constraint *dest_constraints = NULL;
  size_t j, ndest_constraints = 0, ncerts = 0;
  struct sshkey **certs = NULL;
  int cert_only = 0;

  debug2_f("entering");
  if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
      (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0) {
    error_fr(r, "parse");
    goto send;
  }
  if (parse_key_constraints(e->request, NULL, &death, &seconds, &confirm,
      NULL, &dest_constraints, &ndest_constraints, &cert_only,
      &ncerts, &certs) != 0) {
    error_f("failed to parse constraints");
    goto send;
  }
  dump_dest_constraints(__func__, dest_constraints, ndest_constraints);
  if (socket_is_remote(e) && !remote_add_provider) {
    verbose("failed PKCS#11 add of \"%.100s\": remote addition of "
        "providers is disabled", provider);
    goto send;
  }
  if (realpath(provider, canonical_provider) == NULL) {
    verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
        provider, strerror(errno));
    goto send;
  }
  if (match_pattern_list(canonical_provider, allowed_providers, 0) != 1) {
    verbose("refusing PKCS#11 add of \"%.100s\": "
        "provider not allowed", canonical_provider);
    goto send;
  }
  debug_f("add %.100s", canonical_provider);
  if (lifetime && !death)
    death = monotime() + lifetime;

  count = pkcs11_add_provider(canonical_provider, pin, &keys, &comments);
  for (i = 0; i < count; i++) {
    if (comments[i] == NULL || comments[i][0] == '\0') {
      free(comments[i]);
      comments[i] = xstrdup(canonical_provider);
    }
    for (j = 0; j < ncerts; j++) {
      if (!sshkey_is_cert(certs[j]))
        continue;
      if (!sshkey_equal_public(keys[i], certs[j]))
        continue;
      if (pkcs11_make_cert(keys[i], certs[j], &k) != 0)
        continue;
      add_p11_identity(k, xstrdup(comments[i]),
          canonical_provider, death, confirm,
          dest_constraints, ndest_constraints);
      success = 1;
    }
    if (!cert_only && lookup_identity(keys[i]) == NULL) {
      add_p11_identity(keys[i], comments[i],
          canonical_provider, death, confirm,
          dest_constraints, ndest_constraints);
      keys[i] = NULL;   /* transferred */
      comments[i] = NULL; /* transferred */
      success = 1;
    }
    /* XXX update constraints for existing keys */
    sshkey_free(keys[i]);
    free(comments[i]);
  }
send:
  free(pin);
  free(provider);
  free(keys);
  free(comments);
  free_dest_constraints(dest_constraints, ndest_constraints);
  for (j = 0; j < ncerts; j++)
    sshkey_free(certs[j]);
  free(certs);
  send_status(e, success);
}

static void
process_remove_smartcard_key(SocketEntry *e)
{
  char *provider = NULL, *pin = NULL, canonical_provider[PATH_MAX];
  int r, success = 0;
  Identity *id, *nxt;

  debug2_f("entering");
  if ((r = sshbuf_get_cstring(e->request, &provider, NULL)) != 0 ||
      (r = sshbuf_get_cstring(e->request, &pin, NULL)) != 0) {
    error_fr(r, "parse");
    goto send;
  }
  free(pin);

  if (realpath(provider, canonical_provider) == NULL) {
    verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
        provider, strerror(errno));
    goto send;
  }

  debug_f("remove %.100s", canonical_provider);
  for (id = TAILQ_FIRST(&idtab->idlist); id; id = nxt) {
    nxt = TAILQ_NEXT(id, next);
    /* Skip file--based keys */
    if (id->provider == NULL)
      continue;
    if (!strcmp(canonical_provider, id->provider)) {
      TAILQ_REMOVE(&idtab->idlist, id, next);
      free_identity(id);
      idtab->nentries--;
    }
  }
  if (pkcs11_del_provider(canonical_provider) == 0)
    success = 1;
  else
    error_f("pkcs11_del_provider failed");
send:
  free(provider);
  send_status(e, success);
}
#endif /* ENABLE_PKCS11 */

static int
process_ext_session_bind(SocketEntry *e)
{
  int r, sid_match, key_match;
  struct sshkey *key = NULL;
  struct sshbuf *sid = NULL, *sig = NULL;
  char *fp = NULL;
  size_t i;
  u_char fwd = 0;

  debug2_f("entering");
  e->session_bind_attempted = 1;
  if ((r = sshkey_froms(e->request, &key)) != 0 ||
      (r = sshbuf_froms(e->request, &sid)) != 0 ||
      (r = sshbuf_froms(e->request, &sig)) != 0 ||
      (r = sshbuf_get_u8(e->request, &fwd)) != 0) {
    error_fr(r, "parse");
    goto out;
  }
  if (sshbuf_len(sid) > AGENT_MAX_SID_LEN) {
    error_f("session ID too long");
    goto out;
  }
  if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
      SSH_FP_DEFAULT)) == NULL)
    fatal_f("fingerprint failed");
  /* check signature with hostkey on session ID */
  if ((r = sshkey_verify(key, sshbuf_ptr(sig), sshbuf_len(sig),
      sshbuf_ptr(sid), sshbuf_len(sid), NULL, 0, NULL)) != 0) {
    error_fr(r, "sshkey_verify for %s %s", sshkey_type(key), fp);
    goto out;
  }
  /* check whether sid/key already recorded */
  for (i = 0; i < e->nsession_ids; i++) {
    if (!e->session_ids[i].forwarded) {
      error_f("attempt to bind session ID to socket "
          "previously bound for authentication attempt");
      r = -1;
      goto out;
    }
    sid_match = buf_equal(sid, e->session_ids[i].sid) == 0;
    key_match = sshkey_equal(key, e->session_ids[i].key);
    if (sid_match && key_match) {
      debug_f("session ID already recorded for %s %s",
          sshkey_type(key), fp);
      r = 0;
      goto out;
    } else if (sid_match) {
      error_f("session ID recorded against different key "
          "for %s %s", sshkey_type(key), fp);
      r = -1;
      goto out;
    }
    /*
     * new sid with previously-seen key can happen, e.g. multiple
     * connections to the same host.
     */
  }
  /* record new key/sid */
  if (e->nsession_ids >= AGENT_MAX_SESSION_IDS) {
    error_f("too many session IDs recorded");
    r = -1;
    goto out;
  }
  e->session_ids = xrecallocarray(e->session_ids, e->nsession_ids,
      e->nsession_ids + 1, sizeof(*e->session_ids));
  i = e->nsession_ids++;
  debug_f("recorded %s %s (slot %zu of %d)", sshkey_type(key), fp, i,
      AGENT_MAX_SESSION_IDS);
  e->session_ids[i].key = key;
  e->session_ids[i].forwarded = fwd != 0;
  key = NULL; /* transferred */
  /* can't transfer sid; it's refcounted and scoped to request's life */
  if ((e->session_ids[i].sid = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new");
  if ((r = sshbuf_putb(e->session_ids[i].sid, sid)) != 0)
    fatal_fr(r, "sshbuf_putb session ID");
  /* success */
  r = 0;
 out:
  free(fp);
  sshkey_free(key);
  sshbuf_free(sid);
  sshbuf_free(sig);
  return r == 0 ? 1 : 0;
}

static int
process_ext_query(SocketEntry *e)
{
  int r;
  struct sshbuf *msg = NULL;

  debug2_f("entering");
  if ((msg = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  if ((r = sshbuf_put_u8(msg, SSH_AGENT_EXTENSION_RESPONSE)) != 0 ||
      (r = sshbuf_put_cstring(msg, "query")) != 0 ||
      /* string[]     supported extension types */
      (r = sshbuf_put_cstring(msg, "session-bind@openssh.com")) != 0)
    fatal_fr(r, "compose");
  if ((r = sshbuf_put_stringb(e->output, msg)) != 0)
    fatal_fr(r, "enqueue");
  sshbuf_free(msg);
  return 1;
}

static void
process_extension(SocketEntry *e)
{
  int r, replied = 0, success = 0;
  char *name;

  debug2_f("entering");
  if ((r = sshbuf_get_cstring(e->request, &name, NULL)) != 0) {
    error_fr(r, "parse");
    send_status(e, 0);
    return;
  }

  /*
   * This function can be called while the agent is locked to allow
   * session binds to be processed for new channels.
   * Other operations should be refused when locked.
   */

  if (strcmp(name, "session-bind@openssh.com") == 0) {
    success = process_ext_session_bind(e);
  } else if (locked) {
    debug_f("attempt to use extension \"%s\" while locked", name);
    goto generic_fail;
  } else if (strcmp(name, "query") == 0) {
    replied = success = process_ext_query(e);
  } else {
    debug_f("unsupported extension \"%s\"", name);
 generic_fail:
    free(name);
    send_status(e, 0);
    return;
  }
  free(name);
  /* Agent failures are signalled with a different error code */
  if (!replied) {
    send_status_generic(e,
        success ? SSH_AGENT_SUCCESS : SSH_AGENT_EXTENSION_FAILURE);
  }
}

/*
 * dispatch incoming message.
 * returns 1 on success, 0 for incomplete messages or -1 on error.
 */
static int
process_message(u_int socknum)
{
  u_int msg_len;
  u_char type;
  const u_char *cp;
  int r;
  SocketEntry *e;

  if (socknum >= sockets_alloc)
    fatal_f("sock %u >= allocated %u", socknum, sockets_alloc);
  e = &sockets[socknum];

  if (sshbuf_len(e->input) < 5)
    return 0;   /* Incomplete message header. */
  cp = sshbuf_ptr(e->input);
  msg_len = PEEK_U32(cp);
  if (msg_len > AGENT_MAX_LEN) {
    debug_f("socket %u (fd=%d) message too long %u > %u",
        socknum, e->fd, msg_len, AGENT_MAX_LEN);
    return -1;
  }
  if (sshbuf_len(e->input) < msg_len + 4)
    return 0;   /* Incomplete message body. */

  /* move the current input to e->request */
  sshbuf_reset(e->request);
  if ((r = sshbuf_get_stringb(e->input, e->request)) != 0 ||
      (r = sshbuf_get_u8(e->request, &type)) != 0) {
    if (r == SSH_ERR_MESSAGE_INCOMPLETE ||
        r == SSH_ERR_STRING_TOO_LARGE) {
      error_fr(r, "parse");
      return -1;
    }
    fatal_fr(r, "parse");
  }

  debug_f("socket %u (fd=%d) type %d", socknum, e->fd, type);

  /* check whether agent is locked */
  if (locked && type != SSH_AGENTC_UNLOCK) {
    switch (type) {
    case SSH2_AGENTC_REQUEST_IDENTITIES:
      /* send empty lists */
      no_identities(e);
      break;
    case SSH_AGENTC_EXTENSION:
      process_extension(e);
      break;
    default:
      /* send a fail message for all other request types */
      send_status(e, 0);
    }
    sshbuf_reset(e->request);
    return 1;
  }

  switch (type) {
  case SSH_AGENTC_LOCK:
  case SSH_AGENTC_UNLOCK:
    process_lock_agent(e, type == SSH_AGENTC_LOCK);
    break;
  case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
    process_remove_all_identities(e); /* safe for !WITH_SSH1 */
    break;
  /* ssh2 */
  case SSH2_AGENTC_SIGN_REQUEST:
    process_sign_request2(e);
    break;
  case SSH2_AGENTC_REQUEST_IDENTITIES:
    process_request_identities(e);
    break;
  case SSH2_AGENTC_ADD_IDENTITY:
  case SSH2_AGENTC_ADD_ID_CONSTRAINED:
    process_add_identity(e);
    break;
  case SSH2_AGENTC_REMOVE_IDENTITY:
    process_remove_identity(e);
    break;
  case SSH2_AGENTC_REMOVE_ALL_IDENTITIES:
    process_remove_all_identities(e);
    break;
#ifdef ENABLE_PKCS11
  case SSH_AGENTC_ADD_SMARTCARD_KEY:
  case SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED:
    process_add_smartcard_key(e);
    break;
  case SSH_AGENTC_REMOVE_SMARTCARD_KEY:
    process_remove_smartcard_key(e);
    break;
#endif /* ENABLE_PKCS11 */
  case SSH_AGENTC_EXTENSION:
    process_extension(e);
    break;
  default:
    /* Unknown message.  Respond with failure. */
    error("Unknown message %d", type);
    sshbuf_reset(e->request);
    send_status(e, 0);
    break;
  }
  return 1;
}

static void
new_socket(sock_type type, int fd)
{
  u_int i, old_alloc, new_alloc;

  debug_f("type = %s", type == AUTH_CONNECTION ? "CONNECTION" :
      (type == AUTH_SOCKET ? "SOCKET" : "UNKNOWN"));
  set_nonblock(fd);

  if (fd > max_fd)
    max_fd = fd;

  for (i = 0; i < sockets_alloc; i++)
    if (sockets[i].type == AUTH_UNUSED) {
      sockets[i].fd = fd;
      if ((sockets[i].input = sshbuf_new()) == NULL ||
          (sockets[i].output = sshbuf_new()) == NULL ||
          (sockets[i].request = sshbuf_new()) == NULL)
        fatal_f("sshbuf_new failed");
      sockets[i].type = type;
      return;
    }
  old_alloc = sockets_alloc;
  new_alloc = sockets_alloc + 10;
  sockets = xrecallocarray(sockets, old_alloc, new_alloc,
      sizeof(sockets[0]));
  for (i = old_alloc; i < new_alloc; i++)
    sockets[i].type = AUTH_UNUSED;
  sockets_alloc = new_alloc;
  sockets[old_alloc].fd = fd;
  if ((sockets[old_alloc].input = sshbuf_new()) == NULL ||
      (sockets[old_alloc].output = sshbuf_new()) == NULL ||
      (sockets[old_alloc].request = sshbuf_new()) == NULL)
    fatal_f("sshbuf_new failed");
  sockets[old_alloc].type = type;
}

static int
handle_socket_read(u_int socknum)
{
  struct sockaddr_un sunaddr;
  socklen_t slen;
  uid_t euid;
  gid_t egid;
  int fd;

  slen = sizeof(sunaddr);
  fd = accept(sockets[socknum].fd, (struct sockaddr *)&sunaddr, &slen);
  if (fd == -1) {
    error("accept from AUTH_SOCKET: %s", strerror(errno));
    return -1;
  }
  if (getpeereid(fd, &euid, &egid) == -1) {
    error("getpeereid %d failed: %s", fd, strerror(errno));
    close(fd);
    return -1;
  }
  if ((euid != 0) && (getuid() != euid)) {
    error("uid mismatch: peer euid %u != uid %u",
        (u_int) euid, (u_int) getuid());
    close(fd);
    return -1;
  }
  new_socket(AUTH_CONNECTION, fd);
  return 0;
}

static int
handle_conn_read(u_int socknum)
{
  char buf[AGENT_RBUF_LEN];
  ssize_t len;
  int r;

  if ((len = read(sockets[socknum].fd, buf, sizeof(buf))) <= 0) {
    if (len == -1) {
      if (errno == EAGAIN || errno == EINTR)
        return 0;
      error_f("read error on socket %u (fd %d): %s",
          socknum, sockets[socknum].fd, strerror(errno));
    }
    return -1;
  }
  if ((r = sshbuf_put(sockets[socknum].input, buf, len)) != 0)
    fatal_fr(r, "compose");
  explicit_bzero(buf, sizeof(buf));
  for (;;) {
    if ((r = process_message(socknum)) == -1)
      return -1;
    else if (r == 0)
      break;
  }
  return 0;
}

static int
handle_conn_write(u_int socknum)
{
  ssize_t len;
  int r;

  if (sshbuf_len(sockets[socknum].output) == 0)
    return 0; /* shouldn't happen */
  if ((len = write(sockets[socknum].fd,
      sshbuf_ptr(sockets[socknum].output),
      sshbuf_len(sockets[socknum].output))) <= 0) {
    if (len == -1) {
      if (errno == EAGAIN || errno == EINTR)
        return 0;
      error_f("read error on socket %u (fd %d): %s",
          socknum, sockets[socknum].fd, strerror(errno));
    }
    return -1;
  }
  if ((r = sshbuf_consume(sockets[socknum].output, len)) != 0)
    fatal_fr(r, "consume");
  return 0;
}

static void
after_poll(struct pollfd *pfd, size_t npfd, u_int maxfds)
{
  size_t i;
  u_int socknum, activefds = npfd;

  for (i = 0; i < npfd; i++) {
    if (pfd[i].revents == 0)
      continue;
    /* Find sockets entry */
    for (socknum = 0; socknum < sockets_alloc; socknum++) {
      if (sockets[socknum].type != AUTH_SOCKET &&
          sockets[socknum].type != AUTH_CONNECTION)
        continue;
      if (pfd[i].fd == sockets[socknum].fd)
        break;
    }
    if (socknum >= sockets_alloc) {
      error_f("no socket for fd %d", pfd[i].fd);
      continue;
    }
    /* Process events */
    switch (sockets[socknum].type) {
    case AUTH_SOCKET:
      if ((pfd[i].revents & (POLLIN|POLLERR)) == 0)
        break;
      if (npfd > maxfds) {
        debug3("out of fds (active %u >= limit %u); "
            "skipping accept", activefds, maxfds);
        break;
      }
      if (handle_socket_read(socknum) == 0)
        activefds++;
      break;
    case AUTH_CONNECTION:
      if ((pfd[i].revents & (POLLIN|POLLHUP|POLLERR)) != 0 &&
          handle_conn_read(socknum) != 0)
        goto close_sock;
      if ((pfd[i].revents & (POLLOUT|POLLHUP)) != 0 &&
          handle_conn_write(socknum) != 0) {
 close_sock:
        if (activefds == 0)
          fatal("activefds == 0 at close_sock");
        close_socket(&sockets[socknum]);
        activefds--;
        break;
      }
      break;
    default:
      break;
    }
  }
}

static int
prepare_poll(struct pollfd **pfdp, size_t *npfdp, struct timespec *timeoutp, u_int maxfds)
{
  struct pollfd *pfd = *pfdp;
  size_t i, j, npfd = 0;
  time_t deadline;
  int r;

  /* Count active sockets */
  for (i = 0; i < sockets_alloc; i++) {
    switch (sockets[i].type) {
    case AUTH_SOCKET:
    case AUTH_CONNECTION:
      npfd++;
      break;
    case AUTH_UNUSED:
      break;
    default:
      fatal("Unknown socket type %d", sockets[i].type);
      break;
    }
  }
  if (npfd != *npfdp &&
      (pfd = recallocarray(pfd, *npfdp, npfd, sizeof(*pfd))) == NULL)
    fatal_f("recallocarray failed");
  *pfdp = pfd;
  *npfdp = npfd;

  for (i = j = 0; i < sockets_alloc; i++) {
    switch (sockets[i].type) {
    case AUTH_SOCKET:
      if (npfd > maxfds) {
        debug3("out of fds (active %zu >= limit %u); "
            "skipping arming listener", npfd, maxfds);
        break;
      }
      pfd[j].fd = sockets[i].fd;
      pfd[j].revents = 0;
      pfd[j].events = POLLIN;
      j++;
      break;
    case AUTH_CONNECTION:
      pfd[j].fd = sockets[i].fd;
      pfd[j].revents = 0;
      /*
       * Only prepare to read if we can handle a full-size
       * input read buffer and enqueue a max size reply..
       */
      if ((r = sshbuf_check_reserve(sockets[i].input,
          AGENT_RBUF_LEN)) == 0 &&
          (r = sshbuf_check_reserve(sockets[i].output,
          AGENT_MAX_LEN)) == 0)
        pfd[j].events = POLLIN;
      else if (r != SSH_ERR_NO_BUFFER_SPACE)
        fatal_fr(r, "reserve");
      if (sshbuf_len(sockets[i].output) > 0)
        pfd[j].events |= POLLOUT;
      j++;
      break;
    default:
      break;
    }
  }
  deadline = reaper();
  if (parent_alive_interval != 0)
    deadline = (deadline == 0) ? parent_alive_interval :
        MINIMUM(deadline, parent_alive_interval);
  if (deadline != 0)
    ptimeout_deadline_sec(timeoutp, deadline);
  return (1);
}

static void
cleanup_socket(void)
{
  if (cleanup_pid != 0 && getpid() != cleanup_pid)
    return;
  debug_f("cleanup");
  if (socket_name != NULL) {
    unlink(socket_name);
    free(socket_name);
    socket_name = NULL;
  }
  if (socket_dir[0])
    rmdir(socket_dir);
}

void
cleanup_exit(int i)
{
  cleanup_socket();
#ifdef ENABLE_PKCS11
  pkcs11_terminate();
#endif
  _exit(i);
}

static void
cleanup_handler(int sig)
{
  signalled_exit = sig;
}

static void
keydrop_handler(int sig)
{
  signalled_keydrop = sig;
}

static void
check_parent_exists(void)
{
  /*
   * If our parent has exited then getppid() will return (pid_t)1,
   * so testing for that should be safe.
   */
  if (parent_pid != -1 && getppid() != parent_pid) {
    /* printf("Parent has died - Authentication agent exiting.\n"); */
    cleanup_socket();
    _exit(2);
  }
}

static void
usage(void)
{
  fprintf(stderr,
      "usage: ssh-agent [-c | -s] [-DdTU] [-a bind_address] [-E fingerprint_hash]\n"
      "                 [-O option] [-P allowed_providers] [-t life]\n"
      "       ssh-agent [-TU] [-a bind_address] [-E fingerprint_hash] [-O option]\n"
      "                 [-P allowed_providers] [-t life] command [arg ...]\n"
      "       ssh-agent [-c | -s] -k\n"
      "       ssh-agent -u\n"
      "       ssh-agent -V\n");
  exit(1);
}

int
main(int ac, char **av)
{
  int c_flag = 0, d_flag = 0, D_flag = 0, k_flag = 0;
  int s_flag = 0, T_flag = 0, u_flag = 0, U_flag = 0;
  int sock = -1, ch, result, saved_errno;
  pid_t pid;
  char *homedir = NULL, *shell, *format, *pidstr, *agentsocket = NULL;
  char *cp, pidstrbuf[1 + 3 * sizeof pid];
  char *fdstr;
  const char *errstr = NULL;
  const char *ccp;
#ifdef HAVE_SETRLIMIT
  struct rlimit rlim;
#endif
  extern int optind;
  extern char *optarg;
  size_t len;
  mode_t prev_mask;
  struct timespec timeout;
  struct pollfd *pfd = NULL;
  size_t npfd = 0;
  u_int maxfds;
  sigset_t nsigset, osigset;
  int socket_activated = 0;

  /* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
  sanitise_stdfd();

  /* drop */
  (void)setegid(getgid());
  (void)setgid(getgid());

  platform_disable_tracing(0);  /* strict=no */

#ifdef RLIMIT_NOFILE
  if (getrlimit(RLIMIT_NOFILE, &rlim) == -1)
    fatal("%s: getrlimit: %s", __progname, strerror(errno));
#endif

  __progname = ssh_get_progname(av[0]);
  seed_rng();

  while ((ch = getopt(ac, av, "cDdksTuUVE:a:O:P:t:")) != -1) {
    switch (ch) {
    case 'E':
      fingerprint_hash = ssh_digest_alg_by_name(optarg);
      if (fingerprint_hash == -1)
        fatal("Invalid hash algorithm \"%s\"", optarg);
      break;
    case 'c':
      if (s_flag)
        usage();
      c_flag++;
      break;
    case 'k':
      k_flag++;
      break;
    case 'O':
      if (strcmp(optarg, "no-restrict-websafe") == 0)
        restrict_websafe = 0;
      else if (strcmp(optarg, "allow-remote-pkcs11") == 0)
        remote_add_provider = 1;
      else if ((ccp = strprefix(optarg,
          "websafe-allow=", 0)) != NULL) {
        if (websafe_allowlist != NULL)
          fatal("websafe-allow already set");
        websafe_allowlist = xstrdup(ccp);
      } else
        fatal("Unknown -O option");
      break;
    case 'P':
      if (allowed_providers != NULL)
        fatal("-P option already specified");
      allowed_providers = xstrdup(optarg);
      break;
    case 's':
      if (c_flag)
        usage();
      s_flag++;
      break;
    case 'd':
      if (d_flag || D_flag)
        usage();
      d_flag++;
      break;
    case 'D':
      if (d_flag || D_flag)
        usage();
      D_flag++;
      break;
    case 'a':
      agentsocket = optarg;
      break;
    case 't':
      if ((lifetime = convtime(optarg)) == -1) {
        fprintf(stderr, "Invalid lifetime\n");
        usage();
      }
      break;
    case 'T':
      T_flag++;
      break;
    case 'u':
      u_flag++;
      break;
    case 'U':
      U_flag++;
      break;
    case 'V':
      fprintf(stderr, "%s, %s\n",
          SSH_VERSION, SSH_OPENSSL_VERSION);
      exit(0);
    default:
      usage();
    }
  }
  ac -= optind;
  av += optind;

  if (ac > 0 &&
      (c_flag || k_flag || s_flag || d_flag || D_flag || u_flag))
    usage();

  log_init(__progname,
      d_flag ? SYSLOG_LEVEL_DEBUG3 : SYSLOG_LEVEL_INFO,
      SYSLOG_FACILITY_AUTH, 1);

  if (allowed_providers == NULL)
    allowed_providers = xstrdup(DEFAULT_ALLOWED_PROVIDERS);
  if (websafe_allowlist == NULL)
    websafe_allowlist = xstrdup(DEFAULT_WEBSAFE_ALLOWLIST);

  if (ac == 0 && !c_flag && !s_flag) {
    shell = getenv("SHELL");
    if (shell != NULL && (len = strlen(shell)) > 2 &&
        strncmp(shell + len - 3, "csh", 3) == 0)
      c_flag = 1;
  }
  if (k_flag) {
    pidstr = getenv(SSH_AGENTPID_ENV_NAME);
    if (pidstr == NULL) {
      fprintf(stderr, "%s not set, cannot kill agent\n",
          SSH_AGENTPID_ENV_NAME);
      exit(1);
    }
    pid = (int)strtonum(pidstr, 2, INT_MAX, &errstr);
    if (errstr) {
      fprintf(stderr,
          "%s=\"%s\", which is not a good PID: %s\n",
          SSH_AGENTPID_ENV_NAME, pidstr, errstr);
      exit(1);
    }
    if (kill(pid, SIGTERM) == -1) {
      perror("kill");
      exit(1);
    }
    format = c_flag ? "unsetenv %s;\n" : "unset %s;\n";
    printf(format, SSH_AUTHSOCKET_ENV_NAME);
    printf(format, SSH_AGENTPID_ENV_NAME);
    printf("echo Agent pid %ld killed;\n", (long)pid);
    exit(0);
  }
  if (u_flag) {
    if ((homedir = get_homedir()) == NULL)
      fatal("Couldn't determine home directory");
    agent_cleanup_stale(homedir, u_flag > 1);
    printf("Deleted stale agent sockets in ~/%s\n",
        _PATH_SSH_AGENT_SOCKET_DIR);
    exit(0);
  }

  /*
   * Minimum file descriptors:
   * stdio (3) + listener (1) + syslog (1 maybe) + connection (1) +
   * a few spare for libc / stack protectors / sanitisers, etc.
   */
#define SSH_AGENT_MIN_FDS (3+1+1+1+4)
  if (rlim.rlim_cur < SSH_AGENT_MIN_FDS)
    fatal("%s: file descriptor rlimit %lld too low (minimum %u)",
        __progname, (long long)rlim.rlim_cur, SSH_AGENT_MIN_FDS);
  maxfds = rlim.rlim_cur - SSH_AGENT_MIN_FDS;

  parent_pid = getpid();

  /* Has the socket been provided via socket activation? */
  if (agentsocket == NULL && ac == 0 && (d_flag || D_flag) &&
      (pidstr = getenv("LISTEN_PID")) != NULL &&
      (fdstr = getenv("LISTEN_FDS")) != NULL) {
    if (strcmp(fdstr, "1") != 0) {
      fatal("unexpected LISTEN_FDS contents "
          "(want: \"1\" got\"%s\"", fdstr);
    }
    if (fcntl(3, F_GETFL) == -1)
      fatal("LISTEN_FDS set but fd 3 unavailable");
    pid = (int)strtonum(pidstr, 1, INT_MAX, &errstr);
    if (errstr != NULL)
      fatal("invalid LISTEN_PID: %s", errstr);
    if (pid != getpid())
      fatal("bad LISTEN_PID: %d vs pid %d", pid, getpid());
    debug("using socket activation on fd=3");
    sock = 3;
    socket_activated = 1;
  }

  if (sock == -1 && agentsocket == NULL && !T_flag) {
    /* Default case: ~/.ssh/agent/[socket] */
    if ((homedir = get_homedir()) == NULL)
      fatal("Couldn't determine home directory");
    if (!U_flag)
      agent_cleanup_stale(homedir, 0);
    if (agent_listener(homedir, "agent", &sock, &socket_name) != 0)
      fatal_f("Couldn't prepare agent socket");
    free(homedir);
  } else if (sock == -1) {
    if (T_flag) {
      /*
       * Create private directory for agent socket
       * in $TMPDIR.
       */
      mktemp_proto(socket_dir, sizeof(socket_dir));
      if (mkdtemp(socket_dir) == NULL) {
        perror("mkdtemp: private socket dir");
        exit(1);
      }
      xasprintf(&socket_name, "%s/agent.%ld",
          socket_dir, (long)parent_pid);
    } else {
      /* Try to use specified agent socket */
      socket_dir[0] = '\0';
      socket_name = xstrdup(agentsocket);
    }
    /* Listen on socket */
    prev_mask = umask(0177);
    if ((sock = unix_listener(socket_name,
        SSH_LISTEN_BACKLOG, 0)) < 0) {
      *socket_name = '\0'; /* Don't unlink existing file */
      cleanup_exit(1);
    }
    umask(prev_mask);
  }

  closefrom(sock == -1 ? STDERR_FILENO + 1 : sock + 1);

  /*
   * Create socket early so it will exist before command gets run from
   * the parent.
   */
  if (sock == -1) {
    prev_mask = umask(0177);
    sock = unix_listener(socket_name, SSH_LISTEN_BACKLOG, 0);
    if (sock < 0) {
      /* XXX - unix_listener() calls error() not perror() */
      *socket_name = '\0'; /* Don't unlink existing file */
      cleanup_exit(1);
    }
    umask(prev_mask);
  }

  /*
   * Fork, and have the parent execute the command, if any, or present
   * the socket data.  The child continues as the authentication agent.
   */
  if (D_flag || d_flag) {
    log_init(__progname,
        d_flag ? SYSLOG_LEVEL_DEBUG3 : SYSLOG_LEVEL_INFO,
        SYSLOG_FACILITY_AUTH, 1);
    if (socket_name != NULL) {
      cp = argv_assemble(1, &socket_name);
      format = c_flag ?
          "setenv %s %s;\n" : "%s=%s; export %s;\n";
      printf(format, SSH_AUTHSOCKET_ENV_NAME, cp,
          SSH_AUTHSOCKET_ENV_NAME);
      free(cp);
      printf("echo Agent pid %ld;\n", (long)parent_pid);
      fflush(stdout);
    }
    goto skip;
  }
  pid = fork();
  if (pid == -1) {
    perror("fork");
    cleanup_exit(1);
  }
  if (pid != 0) {   /* Parent - execute the given command. */
    close(sock);
    snprintf(pidstrbuf, sizeof pidstrbuf, "%ld", (long)pid);
    if (ac == 0) {
      format = c_flag ? "setenv %s %s;\n" : "%s=%s; export %s;\n";
      cp = argv_assemble(1, &socket_name);
      printf(format, SSH_AUTHSOCKET_ENV_NAME, cp,
          SSH_AUTHSOCKET_ENV_NAME);
      printf(format, SSH_AGENTPID_ENV_NAME, pidstrbuf,
          SSH_AGENTPID_ENV_NAME);
      free(cp);
      printf("echo Agent pid %ld;\n", (long)pid);
      exit(0);
    }
    if (setenv(SSH_AUTHSOCKET_ENV_NAME, socket_name, 1) == -1 ||
        setenv(SSH_AGENTPID_ENV_NAME, pidstrbuf, 1) == -1) {
      perror("setenv");
      exit(1);
    }
    execvp(av[0], av);
    perror(av[0]);
    exit(1);
  }
  /* child */
  log_init(__progname, SYSLOG_LEVEL_INFO, SYSLOG_FACILITY_AUTH, 0);

  if (setsid() == -1) {
    error("setsid: %s", strerror(errno));
    cleanup_exit(1);
  }

  (void)chdir("/");
  if (stdfd_devnull(1, 1, 1) == -1)
    error_f("stdfd_devnull failed");

#ifdef HAVE_SETRLIMIT
  /* deny core dumps, since memory contains unencrypted private keys */
  rlim.rlim_cur = rlim.rlim_max = 0;
  if (setrlimit(RLIMIT_CORE, &rlim) == -1) {
    error("setrlimit RLIMIT_CORE: %s", strerror(errno));
    cleanup_exit(1);
  }
#endif

skip:

  cleanup_pid = getpid();

#ifdef ENABLE_PKCS11
  pkcs11_init(0);
#endif
  new_socket(AUTH_SOCKET, sock);
  if (ac > 0)
    parent_alive_interval = 10;
  idtab_init();
  ssh_signal(SIGPIPE, SIG_IGN);
  ssh_signal(SIGINT, (d_flag | D_flag) ? cleanup_handler : SIG_IGN);
  ssh_signal(SIGHUP, cleanup_handler);
  ssh_signal(SIGTERM, cleanup_handler);
  ssh_signal(SIGUSR1, keydrop_handler);

  sigemptyset(&nsigset);
  sigaddset(&nsigset, SIGINT);
  sigaddset(&nsigset, SIGHUP);
  sigaddset(&nsigset, SIGTERM);
  sigaddset(&nsigset, SIGUSR1);

  if (socket_name != NULL && unveil(socket_name, "c") == -1) {
    fatal("%s: unveil %s %s", __progname, socket_name,
        strerror(errno));
  }
  if (*socket_dir != '\0' && unveil(socket_dir, "c") == -1) {
    fatal("%s: unveil %s %s", __progname, socket_dir,
        strerror(errno));
  }
  if (unveil("/", "r") == -1)
    fatal("%s: unveil /: %s", __progname, strerror(errno));
  if ((ccp = getenv("SSH_SK_HELPER")) == NULL || *ccp == '\0')
    ccp = _PATH_SSH_SK_HELPER;
  if (unveil(ccp, "x") == -1)
    fatal("%s: unveil %s: %s", __progname, ccp, strerror(errno));
  if ((ccp = getenv("SSH_PKCS11_HELPER")) == NULL || *ccp == '\0')
    ccp = _PATH_SSH_PKCS11_HELPER;
  if (unveil(ccp, "x") == -1)
    fatal("%s: unveil %s: %s", __progname, ccp, strerror(errno));
  if ((ccp = getenv("SSH_ASKPASS")) == NULL || *ccp == '\0')
    ccp = _PATH_SSH_ASKPASS_DEFAULT;
  if (unveil(ccp, "x") == -1)
    fatal("%s: unveil %s: %s", __progname, ccp, strerror(errno));
  if (unveil("/dev/null", "rw") == -1)
    fatal("%s: unveil /dev/null: %s", __progname, strerror(errno));
  if (pledge("stdio rpath cpath wpath unix id proc exec", NULL) == -1)
    fatal("%s: pledge: %s", __progname, strerror(errno));
  platform_pledge_agent();

  while (1) {
    sigprocmask(SIG_BLOCK, &nsigset, &osigset);
    if (signalled_exit != 0) {
      logit("exiting on signal %d", (int)signalled_exit);
      cleanup_exit((signalled_exit == SIGTERM &&
          socket_activated) ? 0 : 2);
    }
    if (signalled_keydrop) {
      logit("signal %d received; removing all keys",
          (int)signalled_keydrop);
      remove_all_identities();
      signalled_keydrop = 0;
    }
    ptimeout_init(&timeout);
    prepare_poll(&pfd, &npfd, &timeout, maxfds);
    result = ppoll(pfd, npfd, ptimeout_get_tsp(&timeout), &osigset);
    sigprocmask(SIG_SETMASK, &osigset, NULL);
    saved_errno = errno;
    if (parent_alive_interval != 0)
      check_parent_exists();
    (void) reaper();  /* remove expired keys */
    if (result == -1) {
      if (saved_errno == EINTR)
        continue;
      fatal("poll: %s", strerror(saved_errno));
    } else if (result > 0)
      after_poll(pfd, npfd, maxfds);
  }
  /* NOTREACHED */
}

Coverage Report

Created: 2026-08-13 07:14