/* $OpenBSD: misc-agent.c,v 1.6 2025/06/17 01:19:27 djm Exp $ */

/*

 * Copyright (c) 2025 Damien Miller <djm@mindrot.org>

 *

 * Permission to use, copy, modify, and distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR

 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN

 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF

 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 */

#include "includes.h"

#include <sys/types.h>

#include <sys/socket.h>

#include <sys/stat.h>

#include <sys/un.h>

#include <dirent.h>

#include <errno.h>

#include <fcntl.h>

#include <netdb.h>

#include <stdlib.h>

#include <string.h>

#include <time.h>

#include <unistd.h>

#include "digest.h"

#include "log.h"

#include "misc.h"

#include "pathnames.h"

#include "ssh.h"

#include "xmalloc.h"

/* stuff shared by agent listeners (ssh-agent and sshd agent forwarding) */

#define SOCKET_HOSTNAME_HASHLEN 10 /* length of hostname hash in socket path */

/* used for presenting random strings in unix_listener_tmp and hostname_hash */

static const char presentation_chars[] =

    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

/* returns a text-encoded hash of the hostname of specified length (max 64) */

static char *

hostname_hash(size_t len)

{

  char hostname[NI_MAXHOST], p[65];

  u_char hash[64];

  int r;

  size_t l, i;

  l = ssh_digest_bytes(SSH_DIGEST_SHA512);

  if (len > 64) {

    error_f("bad length %zu >= max %zd", len, l);

    return NULL;

  }

  if (gethostname(hostname, sizeof(hostname)) == -1) {

    error_f("gethostname: %s", strerror(errno));

    return NULL;

  }

  if ((r = ssh_digest_memory(SSH_DIGEST_SHA512,

      hostname, strlen(hostname), hash, sizeof(hash))) != 0) {

    error_fr(r, "ssh_digest_memory");

    return NULL;

  }

  memset(p, '\0', sizeof(p));

  for (i = 0; i < l; i++)

    p[i] = presentation_chars[

        hash[i] % (sizeof(presentation_chars) - 1)];

  /* debug3_f("hostname \"%s\" => hash \"%s\"", hostname, p); */

  p[len] = '\0';

  return xstrdup(p);

}

char *

agent_hostname_hash(void)

{

  return hostname_hash(SOCKET_HOSTNAME_HASHLEN);

}

/*

 * Creates a unix listener at a mkstemp(3)-style path, e.g. "/dir/sock.XXXXXX"

 * Supplied path is modified to the actual one used.

 */

static int

unix_listener_tmp(char *path, int backlog)

{

  struct sockaddr_un sunaddr;

  int good, sock = -1;

  size_t i, xstart;

  mode_t prev_mask;

  /* Find first 'X' template character back from end of string */

  xstart = strlen(path);

  while (xstart > 0 && path[xstart - 1] == 'X')

    xstart--;

  memset(&sunaddr, 0, sizeof(sunaddr));

  sunaddr.sun_family = AF_UNIX;

  prev_mask = umask(0177);

  for (good = 0; !good;) {

    sock = -1;

    /* Randomise path suffix */

    for (i = xstart; path[i] != '\0'; i++) {

      path[i] = presentation_chars[

          arc4random_uniform(sizeof(presentation_chars)-1)];

    }

    debug_f("trying path \"%s\"", path);

    if (strlcpy(sunaddr.sun_path, path,

        sizeof(sunaddr.sun_path)) >= sizeof(sunaddr.sun_path)) {

      error_f("path \"%s\" too long for Unix domain socket",

          path);

      break;

    }

    if ((sock = socket(PF_UNIX, SOCK_STREAM, 0)) == -1) {

      error_f("socket: %.100s", strerror(errno));

      break;

    }

    if (bind(sock, (struct sockaddr *)&sunaddr,

        sizeof(sunaddr)) == -1) {

      if (errno == EADDRINUSE) {

        error_f("bind \"%s\": %.100s",

            path, strerror(errno));

        close(sock);

        sock = -1;

        continue;

      }

      error_f("bind \"%s\": %.100s", path, strerror(errno));

      break;

    }

    if (listen(sock, backlog) == -1) {

      error_f("listen \"%s\": %s", path, strerror(errno));

      break;

    }

    good = 1;

  }

  umask(prev_mask);

  if (good) {

    debug3_f("listening on unix socket \"%s\" as fd=%d",

        path, sock);

  } else if (sock != -1) {

    close(sock);

    sock = -1;

  }

  return sock;

}

/*

 * Create a subdirectory under the supplied home directory if it

 * doesn't already exist

 */

static int

ensure_mkdir(const char *homedir, const char *subdir)

{

  char *path;

  xasprintf(&path, "%s/%s", homedir, subdir);

  if (mkdir(path, 0700) == 0)

    debug("created directory %s", path);

  else if (errno != EEXIST) {

    error_f("mkdir %s: %s", path, strerror(errno));

    free(path);

    return -1;

  }

  free(path);

  return 0;

}

static int

agent_prepare_sockdir(const char *homedir)

{

  if (homedir == NULL || *homedir == '\0' ||

      ensure_mkdir(homedir, _PATH_SSH_USER_DIR) != 0 ||

      ensure_mkdir(homedir, _PATH_SSH_AGENT_SOCKET_DIR) != 0)

    return -1;

  return 0;

}

/* Get a path template for an agent socket in the user's homedir */

static char *

agent_socket_template(const char *homedir, const char *tag)

{

  char *hostnamehash, *ret;

  if ((hostnamehash = hostname_hash(SOCKET_HOSTNAME_HASHLEN)) == NULL)

    return NULL;

  xasprintf(&ret, "%s/%s/s.%s.%s.XXXXXXXXXX",

      homedir, _PATH_SSH_AGENT_SOCKET_DIR, hostnamehash, tag);

  free(hostnamehash);

  return ret;

}

int

agent_listener(const char *homedir, const char *tag, int *sockp, char **pathp)

{

  int sock;

  char *path;

  *sockp = -1;

  *pathp = NULL;

  if (agent_prepare_sockdir(homedir) != 0)

    return -1; /* error already logged */

  if ((path = agent_socket_template(homedir, tag)) == NULL)

    return -1; /* error already logged */

  if ((sock = unix_listener_tmp(path, SSH_LISTEN_BACKLOG)) == -1) {

    free(path);

    return -1; /* error already logged */

  }

  /* success */

  *sockp = sock;

  *pathp = path;

  return 0;

}

static int

socket_is_stale(const char *path)

{

  int fd, r;

  struct sockaddr_un sunaddr;

  socklen_t l = sizeof(r);

  /* attempt non-blocking connect on socket */

  memset(&sunaddr, '\0', sizeof(sunaddr));

  sunaddr.sun_family = AF_UNIX;

  if (strlcpy(sunaddr.sun_path, path,

      sizeof(sunaddr.sun_path)) >= sizeof(sunaddr.sun_path)) {

    debug_f("path for \"%s\" too long for sockaddr_un", path);

    return 0;

  }

  if ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) == -1) {

    error_f("socket: %s", strerror(errno));

    return 0;

  }

  set_nonblock(fd);

  /* a socket without a listener should yield an error immediately */

  if (connect(fd, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) == -1) {

    debug_f("connect \"%s\": %s", path, strerror(errno));

    close(fd);

    return 1;

  }

  if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &r, &l) == -1) {

    debug_f("getsockopt: %s", strerror(errno));

    close(fd);

    return 0;

  }

  if (r != 0) {

    debug_f("socket error on %s: %s", path, strerror(errno));

    close(fd);

    return 1;

  }

  close(fd);

  debug_f("socket %s seems still active", path);

  return 0;

}

#ifndef HAVE_FSTATAT

# define fstatat(x, y, buf, z) lstat(path, buf)

#endif

#ifndef HAVE_UNLINKAT

# define unlinkat(x, y, z) unlink(path)

#endif

void

agent_cleanup_stale(const char *homedir, int ignore_hosthash)

{

  DIR *d = NULL;

  struct dirent *dp;

  struct stat sb;

  char *prefix = NULL, *dirpath = NULL, *path = NULL;

  struct timespec now, sub, *mtimp = NULL;

  /* Only consider sockets last modified > 1 hour ago */

  if (clock_gettime(CLOCK_REALTIME, &now) != 0) {

    error_f("clock_gettime: %s", strerror(errno));

    return;

  }

  sub.tv_sec = 60 * 60;

  sub.tv_nsec = 0;

  timespecsub(&now, &sub, &now);

  /* Only consider sockets from the same hostname */

  if (!ignore_hosthash) {

    if ((path = agent_hostname_hash()) == NULL) {

      error_f("couldn't get hostname hash");

      return;

    }

    xasprintf(&prefix, "s.%s.", path);

    free(path);

    path = NULL;

  }

  xasprintf(&dirpath, "%s/%s", homedir, _PATH_SSH_AGENT_SOCKET_DIR);

  if ((d = opendir(dirpath)) == NULL) {

    if (errno != ENOENT)

      error_f("opendir \"%s\": %s", dirpath, strerror(errno));

    goto out;

  }

  path = NULL;

  while ((dp = readdir(d)) != NULL) {

    free(path);

    xasprintf(&path, "%s/%s", dirpath, dp->d_name);

#ifdef HAVE_DIRENT_D_TYPE

    if (dp->d_type != DT_SOCK && dp->d_type != DT_UNKNOWN)

      continue;

#endif

    if (fstatat(dirfd(d), dp->d_name,

        &sb, AT_SYMLINK_NOFOLLOW) != 0 && errno != ENOENT) {

      error_f("stat \"%s/%s\": %s",

          dirpath, dp->d_name, strerror(errno));

      continue;

    }

    if (!S_ISSOCK(sb.st_mode))

      continue;

#ifdef HAVE_STRUCT_STAT_ST_MTIM

    mtimp = &sb.st_mtim;

#else

    sub.tv_sec = sb.st_mtime;

    sub.tv_nsec = 0;

    mtimp = ⊂

#endif

    if (timespeccmp(mtimp, &now, >)) {

      debug3_f("Ignoring recent socket \"%s/%s\"",

          dirpath, dp->d_name);

      continue;

    }

    if (!ignore_hosthash &&

        strncmp(dp->d_name, prefix, strlen(prefix)) != 0) {

      debug3_f("Ignoring socket \"%s/%s\" "

          "from different host", dirpath, dp->d_name);

      continue;

    }

    if (socket_is_stale(path)) {

      debug_f("cleanup stale socket %s", path);

      unlinkat(dirfd(d), dp->d_name, 0);

    }

  }

 out:

  if (d != NULL)

    closedir(d);

  free(path);

  free(dirpath);

  free(prefix);

}

#undef unlinkat

#undef fstatat