/*
 * ProFTPD - mod_sftp user authentication
 * Copyright (c) 2008-2021 TJ Saunders
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA.
 *
 * As a special exemption, TJ Saunders and other respective copyright holders
 * give permission to link this program with OpenSSL, and distribute the
 * resulting executable, without including the source code for OpenSSL in the
 * source distribution.
 */

#include "mod_sftp.h"
#include "ssh2.h"
#include "packet.h"
#include "msg.h"
#include "disconnect.h"
#include "interop.h"
#include "auth.h"
#include "crypto.h"
#include "cipher.h"
#include "mac.h"
#include "compress.h"
#include "session.h"
#include "keys.h"
#include "keystore.h"
#include "kbdint.h"
#include "utf8.h"
#include "display.h"

/* From response.c */
extern pr_response_t *resp_list, *resp_err_list;

/* This value of 6 is the same default as OpenSSH's MaxAuthTries. */
static unsigned int auth_attempts_max = 6;
static unsigned int auth_attempts = 0;

static pool *auth_pool = NULL;
static char *auth_default_dir = NULL;

static const char *auth_avail_meths = NULL;

/* This is a bitset of flags, used to check on the authentication method
 * used by the client, to see if the requested method is even enabled.
 */
static unsigned int auth_meths_enabled_flags = 0;

static array_header *auth_chains = NULL;

static int auth_sent_userauth_banner_file = FALSE;
static int auth_sent_userauth_success = FALSE;

static const char *auth_user = NULL;
static const char *auth_service = NULL;

static const char *trace_channel = "ssh2";

static struct passwd *dup_passwd(pool *p, struct passwd *pw) {
  struct passwd *res = NULL;

  res = pcalloc(p, sizeof(struct passwd));
  res->pw_name = pstrdup(p, pw->pw_name);
  res->pw_uid = pw->pw_uid;
  res->pw_gid = pw->pw_gid;
  res->pw_gecos = pstrdup(p, pw->pw_gecos);
  res->pw_dir = pstrdup(p, pw->pw_dir);
  res->pw_shell = pstrdup(p, pw->pw_shell);

  return res;
}

static void ensure_open_passwd(pool *p) {
  pr_auth_setpwent(p);
  pr_auth_setgrent(p);

  pr_auth_getpwent(p);
  pr_auth_getgrent(p);
}

static const char *get_default_chdir(pool *p) {
  config_rec *c;
  const char *path = NULL;

  c = find_config(main_server->conf, CONF_PARAM, "DefaultChdir", FALSE);
  while (c != NULL) {
    int res;

    pr_signals_handle();

    if (c->argc < 2) {
      path = c->argv[0];
      break;
    }

    res = pr_expr_eval_group_and(((char **) c->argv) + 1);
    if (res) {
      path = c->argv[0];
      break;
    }

    c = find_config_next(c, c->next, CONF_PARAM, "DefaultChdir", FALSE);
  }

  if (path &&
      *path != '/' &&
      *path != '~') {
    path = pdircat(p, session.cwd, path, NULL);
  }

  if (path != NULL) {
    path = path_subst_uservar(p, &path);
  }

  return path;
}

static const char *get_default_root(pool *p) {
  config_rec *c;
  const char *path = NULL;

  c = find_config(main_server->conf, CONF_PARAM, "DefaultRoot", FALSE);
  while (c) {
    int res;

    pr_signals_handle();

    if (c->argc < 2) {
      path = c->argv[0];
      break;
    }

    res = pr_expr_eval_group_and(((char **) c->argv) + 1);
    if (res) {
      path = c->argv[0];
      break;
    }

    c = find_config_next(c, c->next, CONF_PARAM, "DefaultRoot", FALSE);
  }

  if (path) {
    path = path_subst_uservar(p, &path);

    if (strncmp(path, "/", 2) == 0) {
      path = NULL;

    } else {
      char *real_path;
      int xerrno = 0;

      PRIVS_USER
      real_path = dir_realpath(p, path);
      if (real_path == NULL) {
        xerrno = errno;
      }
      PRIVS_RELINQUISH

      if (real_path) {
        path = real_path;

      } else {
        char interp_path[PR_TUNABLE_PATH_MAX + 1];

        memset(interp_path, '\0', sizeof(interp_path));
        (void) pr_fs_interpolate(path, interp_path, sizeof(interp_path) - 1);

        pr_log_pri(PR_LOG_NOTICE,
          "notice: unable to use DefaultRoot %s (resolved to '%s'): %s",
            path, interp_path,
          strerror(xerrno));
      }
    }
  }

  return path;
}

static void set_userauth_methods(void) {
  config_rec *c;
  register unsigned int i;

  if (auth_chains != NULL) {
    return;
  }

  auth_avail_meths = NULL;
  auth_meths_enabled_flags = 0;

  c = find_config(main_server->conf, CONF_PARAM, "SFTPAuthMethods", FALSE);
  if (c != NULL) {
    /* Sanity checking of the configured methods is done in the postparse
     * event listener; we can use this as-is without fear.
     */
    auth_chains = c->argv[0];

  } else {
    struct sftp_auth_chain *auth_chain;

    auth_chains = make_array(auth_pool, 0, sizeof(struct sftp_auth_chain *));

    c = find_config(main_server->conf, CONF_PARAM, "SFTPAuthorizedUserKeys",
      FALSE);
    if (c != NULL) {
      auth_chain = sftp_auth_chain_alloc(auth_pool);
      sftp_auth_chain_add_method(auth_chain, SFTP_AUTH_FL_METH_PUBLICKEY,
        "publickey", NULL);
      *((struct sftp_auth_chain **) push_array(auth_chains)) = auth_chain;

    } else {
      pr_trace_msg(trace_channel, 9, "no SFTPAuthorizedUserKeys configured, "
        "not offering 'publickey' authentication");
    }

    c = find_config(main_server->conf, CONF_PARAM, "SFTPAuthorizedHostKeys",
      FALSE);
    if (c != NULL) {
      auth_chain = sftp_auth_chain_alloc(auth_pool);
      sftp_auth_chain_add_method(auth_chain, SFTP_AUTH_FL_METH_HOSTBASED,
        "hostbased", NULL);
      *((struct sftp_auth_chain **) push_array(auth_chains)) = auth_chain;

    } else {
      pr_trace_msg(trace_channel, 9, "no SFTPAuthorizedHostKeys configured, "
        "not offering 'hostbased' authentication");
    }

    if (sftp_kbdint_have_drivers() > 0) {
      auth_chain = sftp_auth_chain_alloc(auth_pool);
      sftp_auth_chain_add_method(auth_chain, SFTP_AUTH_FL_METH_KBDINT,
        "keyboard-interactive", NULL);
      *((struct sftp_auth_chain **) push_array(auth_chains)) = auth_chain;

    } else {
      pr_trace_msg(trace_channel, 9, "no kbdint drivers present, not "
        "offering 'keyboard-interactive' authentication");
    }

    /* The 'password' method is always available. */
    auth_chain = sftp_auth_chain_alloc(auth_pool);
    sftp_auth_chain_add_method(auth_chain, SFTP_AUTH_FL_METH_PASSWORD,
      "password", NULL);
    *((struct sftp_auth_chain **) push_array(auth_chains)) = auth_chain;
  }

  for (i = 0 ; i < auth_chains->nelts; i++) {
    struct sftp_auth_chain *auth_chain;
    struct sftp_auth_method *meth;

    auth_chain = ((struct sftp_auth_chain **) auth_chains->elts)[i];
    meth = ((struct sftp_auth_method **) auth_chain->methods->elts)[0];

    if (!(auth_meths_enabled_flags & meth->method_id)) {
      auth_meths_enabled_flags |= meth->method_id;

      if (auth_avail_meths != NULL) {
        auth_avail_meths = pstrcat(auth_pool, auth_avail_meths, ",",
          meth->method_name, NULL);
      } else {
        auth_avail_meths = meth->method_name;
      }
    }
  }

  pr_trace_msg(trace_channel, 9, "offering authentication methods: %s",
    auth_avail_meths);

  /* Prepare the method-specific APIs, too. */
  if (sftp_auth_hostbased_init(auth_pool) < 0) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "error preparing for 'hostbased' authentication: %s", strerror(errno));
  }

  if (sftp_auth_kbdint_init(auth_pool) < 0) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "error preparing for 'keyboard-interactive' authentication: %s",
      strerror(errno));
  }

  if (sftp_auth_password_init(auth_pool) < 0) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "error preparing for 'password' authentication: %s", strerror(errno));
  }

  if (sftp_auth_publickey_init(auth_pool) < 0) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "error preparing for 'publickey' authentication: %s", strerror(errno));
  }
}

static int setup_env(pool *p, const char *user) {
  struct passwd *pw;
  config_rec *c;
  int login_acl, i, res, root_revoke = TRUE, show_symlinks = FALSE, xerrno;
  struct stat st;
  const char *default_chdir, *default_root, *home_dir;
  const char *sess_ttyname = NULL, *xferlog = NULL;
  cmd_rec *cmd;

  session.hide_password = TRUE;

  pw = pr_auth_getpwnam(p, user);
  if (pw == NULL) {
    xerrno = errno;

    /* This is highly unlikely to happen...*/
    pr_log_auth(PR_LOG_NOTICE,
      "USER %s (Login failed): Unable to retrieve user information: %s", user,
      strerror(xerrno));

    errno = xerrno;
    return -1;
  }

  pw = dup_passwd(p, pw);

  if (pw->pw_uid == PR_ROOT_UID) {
    pr_event_generate("mod_auth.root-login", NULL);

    c = find_config(main_server->conf, CONF_PARAM, "RootLogin", FALSE);
    if (c) {
      if (*((int *) c->argv[0]) == FALSE) {
        (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
          "root login attempted, denied by RootLogin configuration");
        pr_log_auth(PR_LOG_NOTICE, "SECURITY VIOLATION: Root login attempted");
        return -1;
      }

    } else {
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "root login attempted, denied by RootLogin configuration");
      pr_log_auth(PR_LOG_NOTICE, "SECURITY VIOLATION: Root login attempted");
      return -1;
    }
  }

  res = pr_auth_is_valid_shell(main_server->conf, pw->pw_shell);
  if (res == FALSE) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "authentication for user '%s' failed: Invalid shell", user);
    pr_log_auth(PR_LOG_NOTICE, "USER %s (Login failed): Invalid shell: '%s'",
      user, pw->pw_shell);
    return -1;
  }

  res = pr_auth_banned_by_ftpusers(main_server->conf, pw->pw_name);
  if (res == TRUE) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "authentication for user '%s' failed: User in " PR_FTPUSERS_PATH, user);
    pr_log_auth(PR_LOG_NOTICE, "USER %s (Login failed): User in "
      PR_FTPUSERS_PATH, pw->pw_name);
    return -1;
  }

  session.user = pstrdup(p, pw->pw_name);
  session.group = pstrdup(p, pr_auth_gid2name(p, pw->pw_gid));

  session.login_uid = pw->pw_uid;
  session.login_gid = pw->pw_gid;

  /* Note that we do NOT need to explicitly call pr_auth_get_home() here;
   * that call already happens in the pr_auth_getpwnam() call above.  To
   * call it again here would cause the home directory to be rewritten twice;
   * depending on the configured rewrite rules, that would lead to an
   * incorrect value (Bug#3421).
   */

  pw->pw_dir = (char *) path_subst_uservar(p, (const char **) &pw->pw_dir);

  if (session.gids == NULL &&
      session.groups == NULL) {
    res = pr_auth_getgroups(p, pw->pw_name, &session.gids, &session.groups);
    if (res < 1) {
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "no supplemental groups found for user '%s'", pw->pw_name);
    }
  }

  login_acl = login_check_limits(main_server->conf, FALSE, TRUE, &i);
  if (!login_acl) {
    pr_log_auth(PR_LOG_NOTICE, "USER %s (Login failed): Limit configuration "
      "denies login", user);
    return -1;
  }

  PRIVS_USER
  home_dir = dir_realpath(p, pw->pw_dir);
  PRIVS_RELINQUISH

  if (home_dir != NULL) {
    sstrncpy(session.cwd, home_dir, sizeof(session.cwd));

  } else {
    sstrncpy(session.cwd, pw->pw_dir, sizeof(session.cwd));
  }

  c = find_config(main_server->conf, CONF_PARAM, "CreateHome", FALSE);
  if (c != NULL) {
    if (*((unsigned char *) c->argv[0]) == TRUE) {
      if (create_home(p, session.cwd, user, pw->pw_uid, pw->pw_gid) < 0) {
        return -1;
      }
    }
  }

  default_chdir = get_default_chdir(p);
  if (default_chdir != NULL) {
    default_chdir = dir_abs_path(p, default_chdir, TRUE);
    sstrncpy(session.cwd, default_chdir, sizeof(session.cwd));
  }

  /* Make sure any <Limit LOGIN> sections still allow access. */
  login_acl = login_check_limits(main_server->conf, FALSE, TRUE, &i);
  if (!login_acl) {
    pr_log_auth(PR_LOG_NOTICE, "USER %s: Limit configuration denies login",
      user);
    return -1;
  }

  resolve_deferred_dirs(main_server);
  fixup_dirs(main_server, CF_DEFER);

  session.wtmp_log = TRUE;

  c = find_config(main_server->conf, CONF_PARAM, "WtmpLog", FALSE);
  if (c &&
      *((unsigned char *) c->argv[0]) == FALSE) {
    session.wtmp_log = FALSE;
  }

  /* As per Bug#3482, we need to disable WtmpLog for FreeBSD 9.0, as
   * an interim measure.
   *
   * The issue is that some platforms update multiple files for a single
   * pututxline(3) call; proftpd tries to update those files manually,
   * do to chroots (after which a pututxline(3) call will fail).  A proper
   * solution requires a separate process, running with the correct
   * privileges, which would handle wtmp logging. The proftpd session
   * processes would send messages to this logging daemon (via Unix domain
   * socket, or FIFO, or TCP socket).
   *
   * Also note that this hack to disable WtmpLog may need to be extended
   * to other platforms in the future.
   */
#if defined(HAVE_UTMPX_H) && \
    defined(__FreeBSD_version) && __FreeBSD_version >= 900007
  if (session.wtmp_log == TRUE) {
    session.wtmp_log = FALSE;

    pr_log_debug(DEBUG5,
      "WtpmLog automatically disabled; see Bug#3482 for details");
  }
#endif

  PRIVS_ROOT

  if (session.wtmp_log) {
    sess_ttyname = pr_session_get_ttyname(p);

    log_wtmp(sess_ttyname, session.user, session.c->remote_name,
      session.c->remote_addr);
  }

#ifdef PR_USE_LASTLOG
  c = find_config(main_server->conf, CONF_PARAM, "UseLastlog", FALSE);
  if (c &&
      *((unsigned char *) c->argv[0]) == TRUE) {
    if (sess_ttyname == NULL) {
      sess_ttyname = pr_session_get_ttyname(p);
    }

    log_lastlog(pw->pw_uid, session.user, sess_ttyname,
      session.c->remote_addr);
  }
#endif /* PR_USE_LASTLOG */

  c = find_config(main_server->conf, CONF_PARAM, "TransferLog", FALSE);
  if (c == NULL) {
    xferlog = PR_XFERLOG_PATH;

  } else {
    xferlog = c->argv[0];
  }

  if (strncasecmp(xferlog, "none", 5) == 0) {
    xferlog_open(NULL);

  } else {
    xferlog_open(xferlog);
  }

  res = set_groups(p, pw->pw_gid, session.gids);
  xerrno = errno;
  PRIVS_RELINQUISH

  if (res < 0) {
    if (xerrno != ENOSYS) {
      pr_log_pri(PR_LOG_WARNING, "unable to set process groups: %s",
        strerror(xerrno));
    }
  }

  default_root = get_default_root(session.pool);
  if (default_root) {
    ensure_open_passwd(p);

    if (pr_auth_chroot(default_root) < 0) {
      pr_log_pri(PR_LOG_WARNING, "unable to set DefaultRoot directory '%s'",
        default_root);
      return -1;
    }

    if (strncmp(session.cwd, default_root, strlen(default_root)) == 0) {
      char *new_cwd;

      new_cwd = &session.cwd[strlen(default_root)];

      if (*new_cwd == '/') {
        new_cwd++;
      }
      session.cwd[0] = '/';

      sstrncpy(&session.cwd[1], new_cwd, sizeof(session.cwd));
    }
  }

  pr_signals_block();
  PRIVS_ROOT
  PRIVS_SETUP(pw->pw_uid, pw->pw_gid)
  pr_signals_unblock();

  /* Should we give up root privs completely here? */
  c = find_config(main_server->conf, CONF_PARAM, "RootRevoke", FALSE);
  if (c != NULL) {
    root_revoke = *((int *) c->argv[0]);

    if (root_revoke == FALSE) {
      pr_log_debug(DEBUG8, MOD_SFTP_VERSION
        ": retaining root privileges per RootRevoke setting");
    }

  } else {
    /* Do a recursive look for any UserOwner directives; honoring that
     * configuration also requires root privs.
     */
    c = find_config(main_server->conf, CONF_PARAM, "UserOwner", TRUE);
    if (c != NULL) {
      pr_log_debug(DEBUG9, MOD_SFTP_VERSION
        ": retaining root privileges per UserOwner setting");
      root_revoke = FALSE;
    }
  }

  if (root_revoke) {
    PRIVS_ROOT
    PRIVS_REVOKE
    session.disable_id_switching = TRUE;
  }

#ifdef HAVE_GETEUID
  if (getegid() != pw->pw_gid ||
      geteuid() != pw->pw_uid) {
    pr_log_pri(PR_LOG_WARNING,
      "process effective IDs do not match expected IDs");
    return -1;
  }
#endif

  if (pw->pw_dir == NULL ||
      strncmp(pw->pw_dir, "", 1) == 0) {
    pr_log_pri(PR_LOG_WARNING, "Home directory for user '%s' is NULL/empty",
      session.user);
    return -1;
  }

  c = find_config(main_server->conf, CONF_PARAM, "ShowSymlinks", FALSE);
  if (c) {
    if (*((unsigned char *) c->argv[0]) == TRUE) {
      show_symlinks = TRUE;
    }
  }

  if (pr_fsio_chdir_canon(session.cwd, !show_symlinks) < 0) {
    xerrno = errno;

    if (session.chroot_path != NULL ||
        default_root != NULL) {

      pr_log_debug(DEBUG2, "unable to chdir to %s (%s), defaulting to chroot "
        "directory %s", session.cwd, strerror(xerrno),
        (session.chroot_path ? session.chroot_path : default_root));

      if (pr_fsio_chdir_canon("/", !show_symlinks) == -1) {
        xerrno = errno;

        pr_log_pri(PR_LOG_NOTICE, "%s chdir(\"/\") failed: %s", session.user,
          strerror(xerrno));
        errno = xerrno;
        return -1;
      }

    } else if (default_chdir) {
      pr_log_debug(DEBUG2, "unable to chdir to %s (%s), defaulting to home "
        "directory %s", session.cwd, strerror(errno), pw->pw_dir);

      if (pr_fsio_chdir_canon(pw->pw_dir, !show_symlinks) == -1) {
        xerrno = errno;

        pr_log_pri(PR_LOG_NOTICE, "%s chdir(\"%s\") failed: %s", session.user,
          session.cwd, strerror(xerrno));
        errno = xerrno;
        return -1;
      }

    } else {
      pr_log_pri(PR_LOG_NOTICE, "%s chdir(\"%s\") failed: %s", session.user,
        session.cwd, strerror(xerrno));
      errno = xerrno;
      return -1;
    }

  } else {
    pr_log_debug(DEBUG10, "changed directory to '%s'", session.cwd);
  }

  sstrncpy(session.cwd, pr_fs_getcwd(), sizeof(session.cwd));
  sstrncpy(session.vwd, pr_fs_getvwd(), sizeof(session.vwd));

  /* Make sure directory config pointers are set correctly */
  cmd = pr_cmd_alloc(p, 1, C_PASS);
  cmd->cmd_class = CL_AUTH|CL_SSH;
  cmd->arg = "";
  dir_check_full(p, cmd, G_NONE, session.cwd, NULL);

  session.proc_prefix = pstrdup(session.pool, session.c->remote_name);
  session.sf_flags = 0;

  pr_log_auth(PR_LOG_INFO, "USER %s: Login successful", user);

  if (pw->pw_uid == PR_ROOT_UID) {
    pr_log_auth(PR_LOG_WARNING, "ROOT SFTP login successful");
  }

  if (pr_fsio_stat(session.cwd, &st) != -1) {
    build_dyn_config(p, session.cwd, &st, TRUE);
  }

  pr_scoreboard_entry_update(session.pid,
    PR_SCORE_USER, session.user,
    PR_SCORE_CWD, session.cwd,
    NULL);

  pr_timer_remove(PR_TIMER_LOGIN, ANY_MODULE);

  auth_default_dir = pstrdup(session.pool, pr_fs_getvwd());

  session.user = pstrdup(session.pool, session.user);

  if (session.group) {
    session.group = pstrdup(session.pool, session.group);
  }

  session.groups = copy_array_str(session.pool, session.groups);

  pr_resolve_fs_map();
  return 0;
}

static int send_userauth_banner_file(void) {
  struct ssh2_packet *pkt;
  char *path;
  unsigned char *buf, *ptr;
  const char *msg;
  int res;
  uint32_t buflen, bufsz;
  config_rec *c;
  pr_fh_t *fh;
  pool *sub_pool;
  struct stat st;

  if (auth_sent_userauth_banner_file) {
    /* Already sent the banner; no need to do it again. */
    return 0;
  }

  c = find_config(main_server->conf, CONF_PARAM, "SFTPDisplayBanner", FALSE);
  if (c == NULL) {
    return 0;
  }
  path = c->argv[0];

  if (!sftp_interop_supports_feature(SFTP_SSH2_FEAT_USERAUTH_BANNER)) {
    pr_trace_msg(trace_channel, 3, "unable to send SFTPDisplayBanner '%s': "
      "USERAUTH_BANNER supported by client", path);
    return 0;
  }

  fh = pr_fsio_open_canon(path, O_RDONLY);
  if (fh == NULL) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "error opening SFTPDisplayBanner '%s': %s", path, strerror(errno));
    return 0;
  }

  res = pr_fsio_fstat(fh, &st);
  if (res < 0) {
    int xerrno = errno;

    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "unable to stat SFTPDisplayBanner '%s': %s", path, strerror(xerrno));

    pr_fsio_close(fh);
    return 0;
  }

  if (S_ISDIR(st.st_mode)) {
    int xerrno = EISDIR;

    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "unable to use SFTPDisplayBanner '%s': %s", path, strerror(xerrno));
    
    pr_fsio_close(fh);
    return 0;
  }

  sub_pool = make_sub_pool(auth_pool);
  pr_pool_tag(sub_pool, "SSH2 auth banner pool");

  msg = sftp_display_fh_get_msg(sub_pool, fh);
  pr_fsio_close(fh);

  if (msg == NULL) {
    destroy_pool(sub_pool);
    return -1;
  }

  pr_trace_msg(trace_channel, 3,
    "sending userauth banner from SFTPDisplayBanner file '%s'", path);

  pkt = sftp_ssh2_packet_create(sub_pool);

  buflen = bufsz = strlen(msg) + 32;
  ptr = buf = palloc(pkt->pool, bufsz);

  sftp_msg_write_byte(&buf, &buflen, SFTP_SSH2_MSG_USER_AUTH_BANNER);
  sftp_msg_write_string(&buf, &buflen, msg);

  /* XXX locale of banner */
  sftp_msg_write_string(&buf, &buflen, "");

  pkt->payload = ptr;
  pkt->payload_len = (bufsz - buflen);

  res = sftp_ssh2_packet_write(sftp_conn->wfd, pkt);
  destroy_pool(pkt->pool);

  if (res < 0) {
    destroy_pool(sub_pool);
    return -1;
  }

  auth_sent_userauth_banner_file = TRUE;
  destroy_pool(sub_pool);
  return 0;
}

static int send_userauth_failure(char *failed_meth) {
  struct ssh2_packet *pkt;
  unsigned char *buf, *ptr;
  char *meths;
  uint32_t buflen, bufsz = 1024;
  int res;

  pkt = sftp_ssh2_packet_create(auth_pool);

  if (failed_meth) {
    register unsigned int i;

    auth_avail_meths = NULL;
    auth_meths_enabled_flags = 0;

    for (i = 0 ; i < auth_chains->nelts; i++) {
      register unsigned int j;
      struct sftp_auth_chain *auth_chain;
      struct sftp_auth_method *meth = NULL;

      pr_signals_handle();
      auth_chain = ((struct sftp_auth_chain **) auth_chains->elts)[i];

      for (j = 0; j < auth_chain->methods->nelts; j++) {
        struct sftp_auth_method *m;

        m = ((struct sftp_auth_method **) auth_chain->methods->elts)[j];
        if (m->succeeded != TRUE &&
            m->failed != TRUE) {
          meth = m;
          break;
        }
      }

      if (meth == NULL) {
        /* All of the methods in this list have failed; check the next
         * list.
         */
        continue;
      }

      if (strcmp(meth->method_name, failed_meth) != 0) {
        if (!(auth_meths_enabled_flags & meth->method_id)) {
          auth_meths_enabled_flags |= meth->method_id;

          if (auth_avail_meths != NULL) {
            auth_avail_meths = pstrcat(auth_pool, auth_avail_meths, ",",
              meth->method_name, NULL);
          } else {
            auth_avail_meths = meth->method_name;
          }
        }
      } else {
        meth->failed = TRUE;
      }
    }

    if (auth_avail_meths == NULL) {
      /* If there are no more auth methods available, we have to disconnect. */
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "no more auth methods available, disconnecting");
      SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
        NULL);
    }

  } else {
    if (auth_avail_meths == NULL) {
      /* This situation can happen when the authentication method succeeded,
       * BUT the subsequent login actions failed (such as failing to chroot,
       * no such home directory, etc etc).  But we still need a list
       * of authentication methods to send back to the client in this message;
       * we thus use the empty string.
       */
      auth_avail_meths = "";
    }
  }

  meths = pstrdup(pkt->pool, auth_avail_meths);

  buflen = bufsz;
  ptr = buf = palloc(pkt->pool, bufsz);

  sftp_msg_write_byte(&buf, &buflen, SFTP_SSH2_MSG_USER_AUTH_FAILURE);
  sftp_msg_write_string(&buf, &buflen, meths);
  sftp_msg_write_bool(&buf, &buflen, FALSE);

  pkt->payload = ptr;
  pkt->payload_len = (bufsz - buflen);

  (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
    "sending userauth failure; remaining userauth methods: %s", meths);

  res = sftp_ssh2_packet_write(sftp_conn->wfd, pkt);
  if (res < 0) {
    destroy_pool(pkt->pool);
    return -1;
  }

  return 0;
}

static int send_userauth_success(void) {
  struct ssh2_packet *pkt;
  unsigned char *buf, *ptr;
  uint32_t buflen, bufsz = 1024;
  int res;

  if (auth_sent_userauth_success) {
    return 0;
  }

  pkt = sftp_ssh2_packet_create(auth_pool);

  buflen = bufsz;
  ptr = buf = palloc(pkt->pool, bufsz);

  sftp_msg_write_byte(&buf, &buflen, SFTP_SSH2_MSG_USER_AUTH_SUCCESS);

  pkt->payload = ptr;
  pkt->payload_len = (bufsz - buflen);

  (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
    "sending userauth success");

  res = sftp_ssh2_packet_write(sftp_conn->wfd, pkt);
  if (res < 0) {
    destroy_pool(pkt->pool);
    return -1;
  }

  auth_sent_userauth_success = TRUE;

  /* We call the compression init routines here as well, in case the
   * client selected "delayed" compression.
   */
  sftp_compress_init_read(SFTP_COMPRESS_FL_AUTHENTICATED);
  sftp_compress_init_write(SFTP_COMPRESS_FL_AUTHENTICATED);

  return 0;
}

static int set_userauth_success(const char *succeeded_meth) {
  register unsigned int i;
  int completed = FALSE;

  auth_avail_meths = NULL;
  auth_meths_enabled_flags = 0;

  for (i = 0 ; i < auth_chains->nelts; i++) {
    register unsigned int j;
    struct sftp_auth_chain *auth_chain;

    pr_signals_handle();
    auth_chain = ((struct sftp_auth_chain **) auth_chains->elts)[i];

    for (j = 0; j < auth_chain->methods->nelts; j++) {
      struct sftp_auth_method *meth = NULL;

      meth = ((struct sftp_auth_method **) auth_chain->methods->elts)[j];
      if (meth->succeeded != TRUE &&
          meth->failed != TRUE) {

        if (strcmp(meth->method_name, succeeded_meth) == 0) {
          /* TODO: What about submethods, for kbdint drivers? */
          meth->succeeded = TRUE;
        }

        /* Add the next method in the list (if any) to the available methods. */
        j++;
        if (j < auth_chain->methods->nelts) {
          meth = ((struct sftp_auth_method **) auth_chain->methods->elts)[j];

          if (!(auth_meths_enabled_flags & meth->method_id)) {
            auth_meths_enabled_flags |= meth->method_id;

            if (auth_avail_meths != NULL) {
              auth_avail_meths = pstrcat(auth_pool, auth_avail_meths, ",",
                meth->method_name, NULL);
            } else {
              auth_avail_meths = meth->method_name;
            }
          }
        }

        break;
      }
    }
  }

  /* Now, having marked the list items that have succeeded, check each list
   * to see if any has been completed.
   */

  for (i = 0 ; i < auth_chains->nelts; i++) {
    register unsigned int j;
    struct sftp_auth_chain *auth_chain;
    int ok = TRUE;

    pr_signals_handle();
    auth_chain = ((struct sftp_auth_chain **) auth_chains->elts)[i];

    for (j = 0; j < auth_chain->methods->nelts; j++) {
      struct sftp_auth_method *meth = NULL;

      meth = ((struct sftp_auth_method **) auth_chain->methods->elts)[j];
      if (meth->succeeded != TRUE) {
        ok = FALSE;
        break;
      }
    }

    if (ok == TRUE) {
      /* We have a successfully completed list! */
      auth_chain->completed = completed = TRUE;
      break;
    }
  }

  if (completed == TRUE) {
    return 1;
  }

  if (auth_avail_meths == NULL) {
    /* If there are no more auth methods available, we have to disconnect. */
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "no more auth methods available, disconnecting");
    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
      NULL);
  }

  return 0;
}

static int send_userauth_methods(char partial_success) {
  struct ssh2_packet *pkt;
  unsigned char *buf, *ptr;
  uint32_t buflen, bufsz = 1024;
  int res;

  pkt = sftp_ssh2_packet_create(auth_pool);

  buflen = bufsz;
  ptr = buf = palloc(pkt->pool, bufsz);

  (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
    "sending acceptable userauth methods: %s", auth_avail_meths);
  
  sftp_msg_write_byte(&buf, &buflen, SFTP_SSH2_MSG_USER_AUTH_FAILURE);
  sftp_msg_write_string(&buf, &buflen, auth_avail_meths);
  sftp_msg_write_bool(&buf, &buflen, partial_success);

  pkt->payload = ptr;
  pkt->payload_len = (bufsz - buflen);

  res = sftp_ssh2_packet_write(sftp_conn->wfd, pkt);
  if (res < 0) {
    destroy_pool(pkt->pool);
    return -1;
  }

  return 0;
}

static void add_cmd_note(cmd_rec *cmd, const char *key, const char *val) {
  int res;

  res = pr_table_add(cmd->notes, key, val, 0);
  if (res < 0 &&
      errno != EEXIST) {
    pr_trace_msg(trace_channel, 19, "error adding '%s' command note: %s",
      key, strerror(errno));
  }
}

static void remove_cmd_note(cmd_rec *cmd, const char *key) {
  (void) pr_table_remove(cmd->notes, key, NULL);
}

static void dispatch_cmd_err(cmd_rec *cmd) {
  pr_response_add_err(R_530, "Login incorrect.");
  pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
  pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
  pr_response_clear(&resp_err_list);
}

static void dispatch_nonfatal_pass(cmd_rec *cmd, const char *method) {
  const char *note = "mod_sftp.nonfatal-attempt";

  add_cmd_note(cmd, note, method);
  dispatch_cmd_err(cmd);
  remove_cmd_note(cmd, note);
}

static void incr_auth_attempts(const char *user, cmd_rec *pass_cmd) {
  auth_attempts++;

  if (auth_attempts_max > 0 &&
      auth_attempts >= auth_attempts_max) {
    pr_log_auth(PR_LOG_NOTICE,
      "Maximum login attempts (%u) exceeded, connection refused",
      auth_attempts_max);
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "Maximum login attempts (%u) exceeded, refusing connection for user '%s'",
      auth_attempts_max, user);

    /* Ensure that the "mod_auth.orig_user" session note exists before
     * dispatching to the PASS error handlers.  Some of them look for this
     * session note (Issue #693).
     */
    if (pr_table_add_dup(session.notes, "mod_auth.orig-user", user, 0) < 0 &&
        errno != EEXIST) {
      pr_log_debug(DEBUG3, "error stashing 'mod_auth.orig-user' in "
        "session.notes: %s", strerror(errno));
    }

    dispatch_cmd_err(pass_cmd);
    pr_event_generate("mod_auth.max-login-attempts", session.c);
    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_BY_APPLICATION, NULL);
  }
}

/* Return -1 on error, 0 to continue, and 1 if the authentication succeeded. */
static int handle_userauth_req(struct ssh2_packet *pkt, char **service) {
  unsigned char *buf;
  const char *orig_user, *user;
  char *method;
  uint32_t buflen;
  cmd_rec *cmd, *user_cmd, *pass_cmd;
  int res, send_userauth_fail = FALSE;
  config_rec *c;

  buf = pkt->payload;
  buflen = pkt->payload_len;

  orig_user = sftp_msg_read_string(pkt->pool, &buf, &buflen);

  user_cmd = pr_cmd_alloc(pkt->pool, 2, pstrdup(pkt->pool, C_USER), orig_user);
  user_cmd->cmd_class = CL_AUTH|CL_SSH;
  user_cmd->arg = (char *) orig_user;

  pass_cmd = pr_cmd_alloc(pkt->pool, 1, pstrdup(pkt->pool, C_PASS));
  pass_cmd->cmd_class = CL_AUTH|CL_SSH;
  pass_cmd->arg = pstrdup(pkt->pool, "(hidden)");

  /* Dispatch these as PRE_CMDs, so that mod_delay's tactics can be used
   * to ameliorate any timing-based attacks.
   */
  if (pr_cmd_dispatch_phase(user_cmd, PRE_CMD, 0) < 0) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "authentication request for user '%s' blocked by '%s' handler",
      orig_user, (char *) user_cmd->argv[0]);

    dispatch_cmd_err(user_cmd);
    return -1;
  }

  if (strcmp(orig_user, user_cmd->arg) == 0) {
    user = orig_user;

  } else {
    user = user_cmd->arg;
  }

  if (auth_user != NULL) {
    /* Check to see if the client has requested a different user name in
     * this USERAUTH_REQUEST.  As per Section 5 of RFC4252, if the user
     * name changes, we can disconnect the client.
     */
    if (strcmp(orig_user, auth_user) != 0) {
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "client used different user name '%s' in USERAUTH_REQUEST (was '%s'), "
        "disconnecting", orig_user, auth_user);

      dispatch_cmd_err(user_cmd);
      return -1;
    }

  } else {
    auth_user = pstrdup(auth_pool, orig_user);
  }

  *service = sftp_msg_read_string(pkt->pool, &buf, &buflen);
  if (auth_service != NULL) {
    /* Check to see if the client has requested a different service name in
     * this USERAUTH_REQUEST.  As per Section 5 of RFC4252, if the service
     * name changes, we can disconnect the client.
     */
    if (strcmp(*service, auth_service) != 0) {
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "client used different service name '%s' in USERAUTH_REQUEST (was "
        "'%s'), disconnecting", *service, auth_service);

      dispatch_cmd_err(user_cmd);
      return -1;
    }

  } else {

    /* Check to see if the requested service is one that we support.
     *
     * As far as I can tell, the only defined 'service names' are:
     *
     *  ssh-userauth (RFC4252)
     *  ssh-connection (RFC4254)
     *
     * If the requested service name is NOT one of the above,
     * we should disconnect, as recommended by RFC4252.
     */

    if (strncmp(*service, "ssh-userauth", 13) == 0 ||
        strncmp(*service, "ssh-connection", 15) == 0) {
      auth_service = pstrdup(auth_pool, *service);

    } else {
      (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
        "client requested unknown/unsupported service name '%s' in "
        "USERAUTH_REQUEST, disconnecting", *service);

      dispatch_cmd_err(user_cmd);
      return -1;
    }
  }

  pr_response_add(R_331, "Password required for %s", user);
  pr_cmd_dispatch_phase(user_cmd, POST_CMD, 0);
  pr_cmd_dispatch_phase(user_cmd, LOG_CMD, 0);
  pr_response_clear(&resp_list);

  method = sftp_msg_read_string(pkt->pool, &buf, &buflen);

  pr_trace_msg(trace_channel, 10, "auth requested for user '%s', service '%s', "
    "using method '%s'", user, *service, method);

  (void) pr_table_remove(session.notes, "mod_auth.orig-user", NULL);
  if (pr_table_add_dup(session.notes, "mod_auth.orig-user", user, 0) < 0 &&
      errno != EEXIST) {
    pr_log_debug(DEBUG3, "error stashing 'mod_auth.orig-user' in "
      "session.notes: %s", strerror(errno));
  }

  cmd = pr_cmd_alloc(pkt->pool, 3, pstrdup(pkt->pool, "USERAUTH_REQUEST"),
    pstrdup(pkt->pool, user), pstrdup(pkt->pool, method));
  cmd->arg = pstrcat(pkt->pool, user, " ", method, NULL);
  cmd->cmd_class = CL_AUTH|CL_SSH;

  if (auth_attempts_max > 0 &&
      auth_attempts > auth_attempts_max) {
    pr_log_auth(PR_LOG_NOTICE,
      "Maximum login attempts (%u) exceeded, connection refused",
      auth_attempts_max);
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "Maximum login attempts (%u) exceeded, refusing connection for user '%s'",
      auth_attempts_max, user);

    /* Ensure that the "mod_auth.orig_user" session note exists before
     * dispatching to the PASS error handlers.  Some of them look for this
     * session note (Issue #693).
     */
    if (pr_table_add_dup(session.notes, "mod_auth.orig-user", user, 0) < 0 &&
        errno != EEXIST) {
      pr_log_debug(DEBUG3, "error stashing 'mod_auth.orig-user' in "
        "session.notes: %s", strerror(errno));
    }

    dispatch_cmd_err(pass_cmd);
    pr_event_generate("mod_auth.max-login-attempts", session.c);
    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_BY_APPLICATION, NULL);
  }

  set_userauth_methods();

  /* Populate the environment for the requested authentication method,
   * so that it can be recorded regardless of success/failure.  Note that
   * the "none" method is not really expected by users, so we deliberately
   * skip/omit that value.
   */
  if (strcmp(method, "none") != 0) {
    pr_env_unset(cmd->pool, "SFTP_USER_AUTH_METHOD");
    pr_env_set(cmd->pool, "SFTP_USER_AUTH_METHOD", method);
    (void) pr_table_add_dup(session.notes, "SFTP_USER_AUTH_METHOD", method, 0);
  }

  /* In order for the actual user password (if any) to be populated properly
   * in the PRE_CMD PASS dispatch (e.g. this is needed for modules like
   * mod_radius; see Bug#3676), the PRE_CMD PASS dispatch needs to happen
   * in the method-specific auth functions, not here.
   *
   * Thus this code will look a little strange; the PRE_CMD PASS dispatching
   * happens in the auth-specific functions, but the POST/LOG_CMD PASS
   * dispatching will happen here.
   */

  if (strncmp(method, "none", 5) == 0) {
    /* If the client requested the "none" auth method at this point, then
     * the list of authentication methods supported by the server is being
     * queried.
     */
    if (send_userauth_methods(FALSE) < 0) {
      pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
      pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
      return -1;
    }

    pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
    pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);
    pr_response_clear(&resp_list);

    return 0;

  } else if (strncmp(method, "publickey", 10) == 0) {
    if (auth_meths_enabled_flags & SFTP_AUTH_FL_METH_PUBLICKEY) {
      int xerrno;

      res = sftp_auth_publickey(pkt, pass_cmd, orig_user, user, *service,
        &buf, &buflen, &send_userauth_fail);
      xerrno = errno;

      if (res < 0) {
        pr_event_generate("mod_sftp.ssh2.auth-publickey.failed", NULL);

      } else {
        pr_event_generate("mod_sftp.ssh2.auth-publickey", NULL);
      }

      errno = xerrno;

    } else {
      pr_trace_msg(trace_channel, 10, "auth method '%s' not enabled", method);

      if (send_userauth_methods(FALSE) < 0) {
        pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
        pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
        return -1;
      }

      pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
      pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

      incr_auth_attempts(user, pass_cmd);
      return 0;
    }

  } else if (strncmp(method, "keyboard-interactive", 21) == 0) {
    if (auth_meths_enabled_flags & SFTP_AUTH_FL_METH_KBDINT) {
      int xerrno = errno;

      res = sftp_auth_kbdint(pkt, pass_cmd, orig_user, user, *service,
        &buf, &buflen, &send_userauth_fail);
      xerrno = errno;

      if (res < 0) {
        pr_event_generate("mod_sftp.ssh2.auth-kbdint.failed", NULL);

      } else {
        pr_event_generate("mod_sftp.ssh2.auth-kbdint", NULL);
      }

      errno = xerrno;

    } else {
      pr_trace_msg(trace_channel, 10, "auth method '%s' not enabled", method);

      if (send_userauth_methods(FALSE) < 0) {
        pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
        pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
        return -1;
      }

      pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
      pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

      incr_auth_attempts(user, pass_cmd);
      return 0;
    }

  } else if (strncmp(method, "password", 9) == 0) {
    if (auth_meths_enabled_flags & SFTP_AUTH_FL_METH_PASSWORD) {
      int xerrno;

      res = sftp_auth_password(pkt, pass_cmd, orig_user, user, *service,
        &buf, &buflen, &send_userauth_fail);
      xerrno = errno;

      if (res < 0) {
        pr_event_generate("mod_sftp.ssh2.auth-password.failed", NULL);

      } else {
        pr_event_generate("mod_sftp.ssh2.auth-password", NULL);
      }

      errno = xerrno;

    } else {
      pr_trace_msg(trace_channel, 10, "auth method '%s' not enabled", method);

      if (send_userauth_methods(FALSE) < 0) {
        pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
        pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
        return -1;
      }

      pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
      pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

      incr_auth_attempts(user, pass_cmd);
      return 0;
    }

  } else if (strncmp(method, "hostbased", 10) == 0) {
    if (auth_meths_enabled_flags & SFTP_AUTH_FL_METH_HOSTBASED) {
      int xerrno;

      res = sftp_auth_hostbased(pkt, pass_cmd, orig_user, user, *service,
        &buf, &buflen, &send_userauth_fail);
      xerrno = errno;

      if (res < 0) {
        pr_event_generate("mod_sftp.ssh2.auth-hostbased.failed", NULL);

      } else {
        pr_event_generate("mod_sftp.ssh2.auth-hostbased", NULL);
      }

      errno = xerrno;

    } else {
      pr_trace_msg(trace_channel, 10, "auth method '%s' not enabled", method);

      if (send_userauth_methods(FALSE) < 0) {
        pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
        pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);
        return -1;
      }

      pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
      pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

      incr_auth_attempts(user, pass_cmd);
      return 0;
    }

  } else {
    pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
    pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);

    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "unsupported authentication method '%s' requested", method);

    incr_auth_attempts(user, pass_cmd);
    return 0;
  }

  /* Make sure that the password cmd_rec arg points back to the static
   * string for passwords.
   */
  pass_cmd->arg = pstrdup(pkt->pool, "(hidden)");

  if (res <= 0) {
    int xerrno = errno;

    /* For a failed authentication _attempt_ (but not yet a real error), we
     * attach a note to this fake PASS "error" command dispatch, so that
     * interested handlers can use it to determine if the command they receive
     * is a real error or not, for e.g. logging/accounting purposes
     * (Issue #693).
     */
    if (res < 0) {
      dispatch_cmd_err(pass_cmd);

    } else {
      dispatch_nonfatal_pass(pass_cmd, method);
    }

    pr_cmd_dispatch_phase(cmd, res == 0 ? POST_CMD : POST_CMD_ERR, 0);
    pr_cmd_dispatch_phase(cmd, res == 0 ? LOG_CMD : LOG_CMD_ERR, 0);

    if (send_userauth_fail) {
      errno = xerrno;

      if (send_userauth_failure(errno != EPERM ? NULL : method) < 0) {
        return -1;
      }

      incr_auth_attempts(user, pass_cmd);
    }

    return res;
  }

  res = set_userauth_success(method);
  if (res == 0) {
    pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
    pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

    if (send_userauth_methods(TRUE) < 0) {
      return -1;
    }

    return res;
  }

  /* Past this point we will not call incr_auth_attempts(); the client has
   * successfully authenticated at this point, and should not be penalized
   * if an internal error causes the rest of the login process to fail.
   * Right?
   */

  if (setup_env(pkt->pool, user) < 0) {
    dispatch_cmd_err(pass_cmd);

    pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
    pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);

    if (send_userauth_failure(NULL) < 0) {
      return -1;
    }

    return 0;
  }

  if (send_userauth_success() < 0) {
    dispatch_cmd_err(pass_cmd);

    pr_cmd_dispatch_phase(cmd, POST_CMD_ERR, 0);
    pr_cmd_dispatch_phase(cmd, LOG_CMD_ERR, 0);

    return -1;
  }

  if (session.auth_mech != NULL) {
    pr_log_debug(DEBUG2, "user '%s' authenticated by %s", user,
      session.auth_mech);
  }

  (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
    "user '%s' authenticated via '%s' method", user, method);

  /* This allows for the %s response code LogFormat variable to be populated
   * in an AUTH ExtendedLog.
   */
  pr_response_add(R_230, "User %s logged in", user);
  pr_cmd_dispatch_phase(pass_cmd, POST_CMD, 0);
  pr_cmd_dispatch_phase(pass_cmd, LOG_CMD, 0);
  pr_response_clear(&resp_list);

  pr_cmd_dispatch_phase(cmd, POST_CMD, 0);
  pr_cmd_dispatch_phase(cmd, LOG_CMD, 0);

  /* At this point, we can look up the Protocols config, which may have
   * been tweaked via mod_ifsession's user/group/class-specific sections.
   */
  c = find_config(main_server->conf, CONF_PARAM, "Protocols", FALSE);
  if (c != NULL) {
    register unsigned int i;
    unsigned int services = 0UL;
    array_header *protocols;
    char **elts; 

    protocols = c->argv[0];
    elts = protocols->elts;

    for (i = 0; i < protocols->nelts; i++) {
      char *protocol;

      protocol = elts[i];
      if (protocol != NULL) {
        if (strncasecmp(protocol, "sftp", 5) == 0) {
          services |= SFTP_SERVICE_FL_SFTP;

        } else if (strncasecmp(protocol, "scp", 4) == 0) {
          services |= SFTP_SERVICE_FL_SCP;

        } else if (strncasecmp(protocol, "date", 5) == 0) {
          services |= SFTP_SERVICE_FL_SCP;
        }
      }
    }

    sftp_services = services;
  }

  return 1;
}

/* Auth Lists API */
struct sftp_auth_chain *sftp_auth_chain_alloc(pool *p) {
  pool *sub_pool;
  struct sftp_auth_chain *auth_chain;

  if (p == NULL) {
    errno = EINVAL;
    return NULL;
  }

  sub_pool = pr_pool_create_sz(p, 256);
  pr_pool_tag(sub_pool, "SSH2 Auth Chain Pool");

  auth_chain = pcalloc(sub_pool, sizeof(struct sftp_auth_chain));
  auth_chain->pool = sub_pool;
  auth_chain->methods = make_array(sub_pool, 1,
    sizeof(struct sftp_auth_method *));
  auth_chain->completed = FALSE;

  return auth_chain;
}

/* Check if 'password' or 'hostbased' methods appear multiple times in
 * this chain; if so, it's an invalid chain.  Multiple 'publickey' or
 * 'keyboard-interactive' methods are allowed, though.
 */
int sftp_auth_chain_isvalid(struct sftp_auth_chain *auth_chain) {
  register unsigned int i;
  int has_password = FALSE, has_hostbased = FALSE;

  for (i = 0; i < auth_chain->methods->nelts; i++) {
    struct sftp_auth_method *meth;

    meth = ((struct sftp_auth_method **) auth_chain->methods->elts)[i];

    switch (meth->method_id) {
      case SFTP_AUTH_FL_METH_PASSWORD:
        if (has_password == TRUE) {
          errno = EPERM;
          return -1;
        }

        has_password = TRUE;
        break;

      case SFTP_AUTH_FL_METH_HOSTBASED:
        if (has_hostbased == TRUE) {
          errno = EPERM;
          return -1;
        }

        has_hostbased = TRUE;
        break;

      case SFTP_AUTH_FL_METH_PUBLICKEY:
      case SFTP_AUTH_FL_METH_KBDINT:
      default:
        break;
    }
  }

  return 0;
}

int sftp_auth_chain_add_method(struct sftp_auth_chain *auth_chain,
    unsigned int method_id, const char *method_name,
    const char *submethod_name) {
  struct sftp_auth_method *meth;

  if (auth_chain == NULL ||
      method_name == NULL) {
    errno = EINVAL;
    return -1;
  }

  /* We currently only allow submethod names for kbdint methods. */
  if (submethod_name != NULL &&
      method_id != SFTP_AUTH_FL_METH_KBDINT) {
    errno = EPERM;
    return -1;
  }

  meth = pcalloc(auth_chain->pool, sizeof(struct sftp_auth_method));
  meth->method_id = method_id;
  meth->method_name = pstrdup(auth_chain->pool, method_name);
  if (submethod_name != NULL) {
    meth->submethod_name = pstrdup(auth_chain->pool, submethod_name);
  }
  meth->succeeded = FALSE;
  meth->failed = FALSE;

  *((struct sftp_auth_method **) push_array(auth_chain->methods)) = meth;
  return 0;
}

int sftp_auth_chain_parse_method(pool *p, const char *name,
    unsigned int *method_id, const char **method_name,
    const char **submethod_name) {
  char *ptr;
  size_t method_namelen;

  if (name == NULL ||
      method_id == NULL ||
      method_name == NULL) {
    errno = EINVAL;
    return -1;
  }

  /* Look for the syntax indicating a submethod name. */
  ptr = strchr(name, ':');
  if (ptr == NULL) {
    method_namelen = strlen(name);
  } else {
    method_namelen = ptr - name - 1;
  }

  if (strncmp(name, "publickey", method_namelen) == 0) {
    *method_id = SFTP_AUTH_FL_METH_PUBLICKEY;
    *method_name = name;

  } else if (strncmp(name, "hostbased", method_namelen) == 0) {
    *method_id = SFTP_AUTH_FL_METH_HOSTBASED;
    *method_name = name;

  } else if (strncmp(name, "password", method_namelen) == 0) {
    *method_id = SFTP_AUTH_FL_METH_PASSWORD;
    *method_name = name;

  } else if (strncmp(name, "keyboard-interactive", method_namelen) == 0) {
    *method_id = SFTP_AUTH_FL_METH_KBDINT;

    if (sftp_kbdint_have_drivers() == 0) {
      errno = EPERM;
      return -1;
    }

    /* If we have a submethod name, check whether it matches one of our
     * loaded kbdint drivers.
     */
    if (ptr != NULL) {
      if (sftp_kbdint_get_driver(ptr) == NULL) {
        errno = EPERM;
        return -1;
      }

      *method_name = pstrndup(p, name, method_namelen);
      if (submethod_name != NULL) {
        *submethod_name = ptr;
      }

    } else {
      *method_name = name;
    }

  } else {
    /* Unknown/unsupported method name. */
    errno = EINVAL;
    return -1;
  }

  return 0;
}

array_header *sftp_auth_chain_parse_method_chain(pool *p,
    const char *method_list) {
  char *ptr;
  size_t method_listlen;
  array_header *method_names;

  if (p == NULL ||
      method_list == NULL) {
    errno = EINVAL;
    return NULL;
  }

  ptr = strchr(method_list, '+');
  if (ptr == NULL) {
    method_names = make_array(p, 0, sizeof(char *));
    *((char **) push_array(method_names)) = pstrdup(p, method_list);
    return method_names;
  }

  if (ptr == method_list) {
    /* Leading '+'. */
    errno = EPERM;
    return NULL;
  }

  method_listlen = strlen(method_list);
  if (method_list[method_listlen-1] == '+') {
    /* Trailing '+'. */
    errno = EPERM;
    return NULL;
  }

  method_names = make_array(p, 0, sizeof(char *));

  while (ptr != NULL) {
    size_t namelen;

    pr_signals_handle();

    namelen = (ptr - method_list);
    if (namelen == 0) {
      /* Double '+' characters. */
      errno = EPERM;
      return NULL;
    }

    *((char **) push_array(method_names)) = pstrndup(p, method_list, namelen);

    method_list = ptr + 1;
    ptr = strchr(method_list, '+');

    /* Don't forget the last name in the list. */
    if (ptr == NULL) {
      *((char **) push_array(method_names)) = pstrdup(p, method_list);
    }
  }

  return method_names;
}

char *sftp_auth_get_default_dir(void) {
  return auth_default_dir;
}

int sftp_auth_send_banner(const char *banner) {
  struct ssh2_packet *pkt;
  unsigned char *buf, *ptr;
  uint32_t buflen, bufsz;
  size_t banner_len;
  int res;

  if (banner == NULL) {
    errno = EINVAL;
    return -1;
  }

  /* If the client has finished authenticating, then we can no longer
   * send USERAUTH_BANNER messages.
   */
  if (sftp_sess_state & SFTP_SESS_STATE_HAVE_AUTH) {
    pr_trace_msg(trace_channel, 1,
      "unable to send banner: client has authenticated");
    return 0;
  }

  /* Make sure that the given banner string ends in CRLF, as required by
   * RFC4252 Section 5.4.
   */
  banner_len = strlen(banner);
  if (banner[banner_len-2] != '\r' ||
      banner[banner_len-1] != '\n') {
    banner = pstrcat(auth_pool, banner, "\r\n", NULL);
    banner_len = strlen(banner);
  }
 
  pkt = sftp_ssh2_packet_create(auth_pool);

  buflen = bufsz = banner_len + 32;
  ptr = buf = palloc(pkt->pool, bufsz);

  sftp_msg_write_byte(&buf, &buflen, SFTP_SSH2_MSG_USER_AUTH_BANNER);
  sftp_msg_write_string(&buf, &buflen, banner);

  /* XXX locale of banner */
  sftp_msg_write_string(&buf, &buflen, "");

  pkt->payload = ptr;
  pkt->payload_len = (bufsz - buflen);

  (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
    "sending userauth banner");

  res = sftp_ssh2_packet_write(sftp_conn->wfd, pkt);
  if (res < 0) {
    destroy_pool(pkt->pool);
    return -1;
  }

  destroy_pool(pkt->pool);
  return 0;
}

int sftp_auth_handle(struct ssh2_packet *pkt) {
  char *service = NULL;
  int res;

  /* The send_userauth_banner_file() function makes sure that the
   * SFTPDisplayBanner file is not sent multiple times.
   */
  if (send_userauth_banner_file() < 0) {
    return -1;
  }

  if (pr_response_get_pool() == NULL) {
    /* We set this pool for use by the Response API, for logging response codes/
     * messages during login.
     */
    pr_response_set_pool(session.pool);
  }

  res = handle_userauth_req(pkt, &service);
  if (res < 0) {
    destroy_pool(pkt->pool);
    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_PROTOCOL_ERROR, NULL);
  }

  destroy_pool(pkt->pool);
  return res;
}

int sftp_auth_init(void) {

  /* There's no point in trying to handle the case where a client will
   * want/attempt to authenticate again, as a different user.
   *
   * The issue is that if a client successfully authenticates, and the
   * authenticated session is chrooted, a subsequent attempt to authenticate
   * will occur in a chrooted process, and that will likely lead to all
   * sorts of brokenness.
   */

  if (auth_pool == NULL) {
    unsigned int *max_logins;

    auth_pool = make_sub_pool(sftp_pool);
    pr_pool_tag(auth_pool, "SSH2 Auth Pool");

    max_logins = get_param_ptr(main_server->conf, "MaxLoginAttempts", FALSE);
    if (max_logins != NULL) {
      auth_attempts_max = *max_logins;
    }
  }

  return 0;
}
