mailutils-3.13/pop3d/pop3d.c

/* GNU Mailutils -- a suite of utilities for electronic mail
   Copyright (C) 1999-2021 Free Software Foundation, Inc.

   GNU Mailutils 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 3, or (at your option)
   any later version.

   GNU Mailutils 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 GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>. */

#include "pop3d.h"
#include "mailutils/pam.h"
#include "mailutils/cli.h"
#include "mailutils/pop3.h"
#include "mailutils/kwd.h"
#include "tcpwrap.h"

mu_mailbox_t mbox;
int state;
char *username;
char *md5shared;

mu_m_server_t server;
unsigned int idle_timeout;
int pop3d_transcript;
int debug_mode;
int pop3d_xlines;
char *apop_database_name = APOP_PASSFILE;
int apop_database_safety = MU_FILE_SAFETY_ALL;
uid_t apop_database_owner;
int apop_database_owner_set;

int initial_state = AUTHORIZATION;

/* Should all the messages be undeleted on startup */
int undelete_on_startup;
#ifdef ENABLE_LOGIN_DELAY
/* Minimum allowed delay between two successive logins */
time_t login_delay = 0;
char *login_stat_file = LOGIN_STAT_FILE;
#endif

unsigned expire = EXPIRE_NEVER; /* Expire messages after this number of days */
int expire_on_exit = 0;         /* Delete expired messages on exit */

const char *program_version = "pop3d (" PACKAGE_STRING ")";

static void
set_foreground (struct mu_parseopt *po, struct mu_option *opt,
		char const *arg)
{
  mu_m_server_set_foreground (server, 1);
}

static void
set_inetd_mode (struct mu_parseopt *po, struct mu_option *opt,
		char const *arg)
{
  mu_m_server_set_mode (server, MODE_INTERACTIVE);
}

static void
set_daemon_mode (struct mu_parseopt *po, struct mu_option *opt,
		 char const *arg)
{
  mu_m_server_set_mode (server, MODE_DAEMON);
  if (arg)
    {
      size_t max_children;
      char *errmsg;
      int rc = mu_str_to_c (arg, mu_c_size, &max_children, &errmsg);
      if (rc)
	{
	  mu_parseopt_error (po, _("%s: bad argument"), arg);
	  exit (po->po_exit_error);
	}
      mu_m_server_set_max_children (server, max_children);
    }
}

static struct mu_option pop3d_options[] = {
  { "foreground",  0, NULL, MU_OPTION_DEFAULT,
    N_("remain in foreground"),
    mu_c_bool, NULL, set_foreground },
  { "inetd",  'i', NULL, MU_OPTION_DEFAULT,
    N_("run in inetd mode"),
    mu_c_bool, NULL, set_inetd_mode },
  { "daemon", 'd', N_("NUMBER"), MU_OPTION_ARG_OPTIONAL,
    N_("runs in daemon mode with a maximum of NUMBER children"),
    mu_c_string, NULL, set_daemon_mode },
  MU_OPTION_END
}, *options[] = { pop3d_options, NULL };

static int
cb_bulletin_source (void *data, mu_config_value_t *val)
{
  if (mu_cfg_assert_value_type (val, MU_CFG_STRING))
    return 1;
  set_bulletin_source (val->v.string); /* FIXME: Error reporting? */
  return 0;
}

static int
cb2_file_safety_checks (const char *name, void *data)
{
  if (mu_file_safety_compose (data, name, MU_FILE_SAFETY_ALL))
    mu_error (_("unknown keyword: %s"), name);
  return 0;
}

static int
cb_apop_safety_checks (void *data, mu_config_value_t *arg)
{
  return mu_cfg_string_value_cb (arg, cb2_file_safety_checks,
				 &apop_database_safety);
}

static int
cb_apop_database_owner (void *data, mu_config_value_t *val)
{
  struct passwd *pw;

  if (mu_cfg_assert_value_type (val, MU_CFG_STRING))
    return 1;
  pw = getpwnam (val->v.string);
  if (!pw)
    {
      char *p;
      unsigned long n;

      n = strtoul (val->v.string, &p, 10);
      if (*p)
	{
	  mu_error (_("no such user: %s"), val->v.string);
	  return 1;
	}
      apop_database_owner = n;
    }
  else
    apop_database_owner = pw->pw_uid;
  apop_database_owner_set = 1;
  return 0;
}

#ifdef ENABLE_DBM
static int
cb_bulletin_db (void *data, mu_config_value_t *val)
{
  if (mu_cfg_assert_value_type (val, MU_CFG_STRING))
    return 1;
  set_bulletin_db (val->v.string); /* FIXME: Error reporting? */
  return 0;
}
#endif

static int
cb_tls (void *data, mu_config_value_t *val)
{
  int *res = data;
  static struct mu_kwd tls_kwd[] = {
    { "no", tls_no },
    { "false", tls_no },
    { "off", tls_no },
    { "0", tls_no },
    { "ondemand", tls_ondemand },
    { "stls", tls_ondemand },
    { "required", tls_required },
    { "connection", tls_connection },
    /* For compatibility with prior versions: */
    { "yes", tls_connection },
    { "true", tls_connection },
    { "on", tls_connection },
    { "1", tls_connection },
    { NULL }
  };

  if (mu_cfg_assert_value_type (val, MU_CFG_STRING))
    return 1;

  if (mu_kwd_xlat_name (tls_kwd, val->v.string, res))
    mu_error (_("not a valid tls keyword: %s"), val->v.string);
  return 0;
}

static struct mu_cfg_param pop3d_srv_param[] = {
  { "tls-mode", mu_cfg_callback,
    NULL, mu_offsetof (struct pop3d_srv_config, tls_mode), cb_tls,
    N_("Kind of TLS encryption to use for this server"),
    /* TRANSLATORS: words to the right of : are keywords - do not translate */
    N_("arg: false|true|ondemand|stls|required|connection") },
  { "tls", mu_cfg_section,
    NULL, mu_offsetof (struct pop3d_srv_config, tls_conf) },
  { NULL }
};

static struct mu_cfg_param pop3d_cfg_param[] = {
  { "undelete", mu_c_bool, &undelete_on_startup, 0, NULL,
    N_("On startup, clear deletion marks from all the messages.") },
  { "expire", mu_c_uint, &expire, 0, NULL,
    N_("Automatically expire read messages after the given number of days."),
    N_("days") },
  { "delete-expired", mu_c_bool, &expire_on_exit, 0, NULL,
    N_("Delete expired messages upon closing the mailbox.") },
  { "scan-lines", mu_c_bool, &pop3d_xlines, 0, NULL,
    N_("Output the number of lines in the message in its scan listing.") },
  { "apop-database-file", mu_c_string, &apop_database_name, 0, NULL,
    N_("set APOP database file name or URL") },
  { "apop-database-owner", mu_cfg_callback, NULL, 0, cb_apop_database_owner,
    N_("Name or UID of the APOP database owner"),
    N_("arg: string") },
  { "apop-database-safety", mu_cfg_callback, NULL, 0, cb_apop_safety_checks,
    N_("Configure safety checks for APOP database files.  Argument is a list or "
       "sequence of check names optionally prefixed with '+' to enable or "
       "'-' to disable the corresponding check.  Valid check names are:\n"
       "\n"
       "  none          disable all checks\n"
       "  all           enable all checks\n"
       "  gwrfil        forbid group writable files\n"
       "  awrfil        forbid world writable files\n"
       "  grdfil        forbid group readable files\n"
       "  ardfil        forbid world writable files\n"
       "  linkwrdir     forbid symbolic links in group or world writable directories\n"
       "  gwrdir        forbid files in group writable directories\n"
       "  awrdir        forbid files in world writable directories\n"),
    N_("arg: list") },

  { "tls", mu_cfg_section, &global_tls_conf },
  { "tls-mode", mu_cfg_callback,
    &global_tls_mode, 0, cb_tls,
    N_("Kind of TLS encryption to use for the inetd server"
       " and all server blocks that lack the tls-mode statement."),
    /* TRANSLATORS: words to the right of : are keywords - do not translate */
    N_("arg: false|true|ondemand|stls|required|connection") },

#ifdef ENABLE_LOGIN_DELAY
  { "login-delay", mu_c_time, &login_delay, 0, NULL,
    N_("Set the minimal allowed delay between two successive logins.") },
  { "stat-file", mu_c_string, &login_stat_file, 0, NULL,
    N_("Set the name of login statistics file (for login-delay).") },
#endif
  { "bulletin-source", mu_cfg_callback, NULL, 0, cb_bulletin_source,
    N_("Get bulletins from the specified mailbox."),
    N_("url: string") },
#ifdef ENABLE_DBM
  { "bulletin-db", mu_cfg_callback, NULL, 0, cb_bulletin_db,
    N_("Set the bulletin database file name."),
    N_("file: string") },
#endif
  { "output-buffer-size", mu_c_size, &pop3d_output_bufsize, 0, NULL,
    N_("Size of the output buffer.") },
  { "mandatory-locking", mu_cfg_section },
  { ".server", mu_cfg_section, NULL, 0, NULL,
    N_("Server configuration.") },
  { "transcript", mu_c_bool, &pop3d_transcript, 0, NULL,
    N_("Set global transcript mode.") },
  TCP_WRAPPERS_CONFIG
  { NULL }
};

static char *capa[] = {
  "auth",
  "debug",
  "mailbox",
  "locking",
  "logging",
  NULL
};

struct mu_cli_setup cli = {
  .optv = options,
  .cfg = pop3d_cfg_param,
  .prog_doc = N_("GNU pop3d -- the POP3 daemon."),
  .server = 1
};

int
pop3d_get_client_address (int fd, struct sockaddr_in *pcs)
{
  mu_diag_output (MU_DIAG_INFO, _("incoming connection opened"));

  /* log information on the connecting client. */
  if (debug_mode)
    {
      mu_diag_output (MU_DIAG_INFO, _("started in debugging mode"));
      return 1;
    }
  else
    {
      socklen_t len = sizeof *pcs;
      if (getpeername (fd, (struct sockaddr*) pcs, &len) < 0)
	{
	  mu_diag_output (MU_DIAG_ERROR,
			  _("cannot obtain IP address of client: %s"),
			  strerror (errno));
	  return 1;
	}
    }
  return 0;
}

/* The main part of the daemon. This function reads input from the client and
   executes the proper functions. Also handles the bulk of error reporting.
   Arguments:
      ifd       --  input descriptor
      ofd       --  output descriptor
      tls       --  initiate encrypted connection */
int
pop3d_mainloop (int ifd, int ofd, struct pop3d_srv_config *cfg)
{
  int status = OK;
  char buffer[512];
  static int sigtab[] = { SIGILL, SIGBUS, SIGFPE, SIGSEGV, SIGSTOP, SIGPIPE,
			  SIGABRT, SIGINT, SIGQUIT, SIGTERM, SIGHUP, SIGALRM };
  struct pop3d_session session;

  mu_set_signals (pop3d_child_signal, sigtab, MU_ARRAY_SIZE (sigtab));

  pop3d_setio (ifd, ofd,
	       cfg->tls_mode == tls_connection ? &cfg->tls_conf : NULL);

  if (cfg->tls_mode == tls_required)
    initial_state = INITIAL;

  state = cfg->tls_mode == tls_connection ? AUTHORIZATION : initial_state;

  pop3d_session_init (&session);
  session.tls_mode = cfg->tls_mode;
  session.tls_conf = &cfg->tls_conf;

  /* FIXME: state should also be in the session? */

  /* Prepare the shared secret for APOP.  */
  {
    char *local_hostname;

    status = mu_get_host_name (&local_hostname);
    if (status)
      {
        mu_diag_funcall (MU_DIAG_ERROR, "mu_get_host_name", NULL, status);
        exit (EXIT_FAILURE);
      }

    md5shared = mu_alloc (strlen (local_hostname) + 51);

    snprintf (md5shared, strlen (local_hostname) + 50, "<%u.%u@%s>", getpid (),
	      (unsigned)time (NULL), local_hostname);
    free (local_hostname);
  }

  /* Lets boogie.  */
  pop3d_outf ("+OK POP3 Ready %s\n", md5shared);

  while (state != UPDATE && state != ABORT)
    {
      char *buf;
      char *arg, *cmd;
      pop3d_command_handler_t handler;

      pop3d_flush_output ();
      status = OK;
      buf = pop3d_readline (buffer, sizeof (buffer));
      pop3d_parse_command (buf, &cmd, &arg);

      if (state == TRANSACTION && !mu_mailbox_is_updated (mbox))
	{
	  static mu_off_t mailbox_size;
	  mu_off_t newsize = 0;
	  mu_mailbox_get_size (mbox, &newsize);
	  /* Did we shrink?  First time save the size.  */
	  if (!mailbox_size)
	    mailbox_size = newsize;
	  else if (newsize < mailbox_size) /* FIXME: Should it be a != ? */
	    pop3d_abquit (ERR_MBOX_SYNC); /* Out of sync, Bail out.  */
	}

      /* Refresh the Lock.  */
      manlock_touchlock (mbox);

      if ((handler = pop3d_find_command (cmd)) != NULL)
	status = handler (arg, &session);
      else
	status = ERR_BAD_CMD;

      if (status != OK)
	pop3d_outf ("-ERR %s\n", pop3d_error_string (status));
    }

  pop3d_session_free (&session);

  pop3d_bye ();

  return status;
}

int
pop3d_connection (int fd, struct sockaddr *sa, int salen,
		  struct mu_srv_config *pconf,
		  void *data)
{
  struct pop3d_srv_config *cfg = (struct pop3d_srv_config *) pconf;

  idle_timeout = cfg->m_cfg.timeout;
  pop3d_transcript = cfg->m_cfg.transcript;

  pop3d_mainloop (fd, fd, cfg);
  return 0;
}

static void
pop3d_alloc_die ()
{
  pop3d_abquit (ERR_NO_MEM);
}

#ifdef ENABLE_DBM
static void
set_dbm_safety ()
{
  mu_url_t hints = mu_dbm_get_hint ();
  const char *param[] = { "+all" };
  mu_url_add_param (hints, 1, param);
}
#endif

int
main (int argc, char **argv)
{
  struct group *gr;
  int status = OK;
  static int sigtab[] = { SIGILL, SIGBUS, SIGFPE, SIGSEGV, SIGSTOP, SIGPIPE };

  /* Native Language Support */
  MU_APP_INIT_NLS ();

  MU_AUTH_REGISTER_ALL_MODULES();
  /* Register the desired formats.  */
  mu_register_local_mbox_formats ();

  mu_tcpwrapper_cfg_init ();
  manlock_cfg_init ();
  mu_acl_cfg_init ();
  mu_tls_cfg_init ();

  mu_m_server_create (&server, program_version);
  mu_m_server_set_config_size (server, sizeof (struct pop3d_srv_config));
  mu_m_server_set_conn (server, pop3d_connection);
  mu_m_server_set_prefork (server, mu_tcp_wrapper_prefork);
  mu_m_server_set_mode (server, MODE_INTERACTIVE);
  mu_m_server_set_max_children (server, 20);
  /* FIXME mu_m_server_set_pidfile (); */
  mu_m_server_set_default_port (server, 110);
  mu_m_server_set_timeout (server, 600);
  mu_m_server_set_strexit (server, mu_strexit);
  mu_m_server_cfg_init (server, pop3d_srv_param);

  mu_alloc_die_hook = pop3d_alloc_die;

  mu_log_syslog = 1;
  manlock_mandatory_locking = 1;

#ifdef ENABLE_DBM
  set_dbm_safety ();
#endif

  mu_cli (argc, argv, &cli, capa, server, &argc, &argv);
  if (argc)
    {
      mu_error (_("too many arguments"));
      exit (EX_USAGE);
    }

  if (expire == 0)
    expire_on_exit = 1;

#ifdef USE_LIBPAM
  if (!mu_pam_service)
    mu_pam_service = "gnu-pop3d";
#endif

  if (mu_m_server_mode (server) == MODE_INTERACTIVE && isatty (0))
    {
      /* If input is a tty, switch to debug mode */
      debug_mode = 1;
    }
  else
    {
      errno = 0;
      gr = getgrnam ("mail");
      if (gr == NULL)
	{
	  if (errno == 0 || errno == ENOENT)
            {
               mu_error (_("%s: no such group"), "mail");
               exit (EX_CONFIG);
            }
          else
            {
	      mu_diag_funcall (MU_DIAG_ERROR, "getgrnam", "mail", errno);
	      exit (EX_OSERR);
            }
	}

      if (setgid (gr->gr_gid) == -1)
	{
	  mu_error (_("error setting mail group: %s"), mu_strerror (errno));
	  exit (EX_OSERR);
	}
    }

  /* Set the signal handlers.  */
  mu_set_signals (pop3d_master_signal, sigtab, MU_ARRAY_SIZE (sigtab));

  mu_stdstream_strerr_setup (mu_log_syslog ?
			     MU_STRERR_SYSLOG : MU_STRERR_STDERR);

  umask (S_IROTH | S_IWOTH | S_IXOTH);	/* 007 */

  /* Check TLS environment, i.e. cert and key files */
  mu_m_server_set_preflight (server, stls_preflight);

  /* Actually run the daemon.  */
  if (mu_m_server_mode (server) == MODE_DAEMON)
    {
      mu_m_server_begin (server);
      status = mu_m_server_run (server);
      mu_m_server_end (server);
      mu_m_server_destroy (&server);
    }
  else
    {
      struct pop3d_srv_config cfg;
      memset (&cfg, 0, sizeof cfg);

      idle_timeout = mu_m_server_timeout (server);

      switch (stls_server_check (&cfg, "<inetd>"))
	{
	case MU_TLS_CONFIG_OK:
	  if (mu_init_tls_libs ())
	    status = EX_OK;
	  else
	    {
	      mu_error (_("TLS is not configured, but requested in the "
			  "configuration"));
	      exit (EX_CONFIG);
	    }
	  break;

	case MU_TLS_CONFIG_NULL:
	  break;

	case MU_TLS_CONFIG_UNSAFE:
	  exit (EX_CONFIG);

	default:
	  exit (EX_UNAVAILABLE);
	}

      /* Make sure we are in the root directory.  */
      chdir ("/");
      status = pop3d_mainloop (MU_STDIN_FD, MU_STDOUT_FD, &cfg);
    }

  if (status)
    mu_error (_("main loop status: %s"), mu_strerror (status));
  /* Close the syslog connection and exit.  */
  closelog ();
  return status ? EX_SOFTWARE : EX_OK;
}