/* Copyright (c) 2003, Roger Dingledine

 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.

 * Copyright (c) 2007-2021, The Tor Project, Inc. */

/* See LICENSE for licensing information */

/**

 * \file setuid.c

 * \brief Change the user ID after Tor has started (Unix only)

 **/

#include "orconfig.h"

#include "lib/process/setuid.h"

#if defined(HAVE_SYS_CAPABILITY_H) && defined(HAVE_CAP_SET_PROC)

#define HAVE_LINUX_CAPABILITIES

#endif

#include "lib/container/smartlist.h"

#include "lib/fs/userdb.h"

#include "lib/log/log.h"

#include "lib/log/util_bug.h"

#include "lib/malloc/malloc.h"

#ifdef HAVE_SYS_TYPES_H

#include <sys/types.h>

#endif

#ifdef HAVE_UNISTD_H

#include <unistd.h>

#endif

#ifdef HAVE_GRP_H

#include <grp.h>

#endif

#ifdef HAVE_PWD_H

#include <pwd.h>

#endif

#ifdef HAVE_SYS_CAPABILITY_H

#include <sys/capability.h>

#endif

#ifdef HAVE_SYS_PRCTL_H

#include <sys/prctl.h>

#endif

#include <errno.h>

#include <string.h>

#ifndef _WIN32

/** Log details of current user and group credentials. Return 0 on

 * success. Logs and return -1 on failure.

 */

static int

log_credential_status(void)

{

/** Log level to use when describing non-error UID/GID status. */

#define CREDENTIAL_LOG_LEVEL LOG_INFO

  /* Real, effective and saved UIDs */

  uid_t ruid, euid, suid;

  /* Read, effective and saved GIDs */

  gid_t rgid, egid, sgid;

  /* Supplementary groups */

  gid_t *sup_gids = NULL;

  int sup_gids_size;

  /* Number of supplementary groups */

  int ngids;

  /* log UIDs */

#ifdef HAVE_GETRESUID

  if (getresuid(&ruid, &euid, &suid) != 0) {

    log_warn(LD_GENERAL, "Error getting changed UIDs: %s", strerror(errno));

    return -1;

  } else {

    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,

           "UID is %u (real), %u (effective), %u (saved)",

           (unsigned)ruid, (unsigned)euid, (unsigned)suid);

  }

#else /* !defined(HAVE_GETRESUID) */

  /* getresuid is not present on MacOS X, so we can't get the saved (E)UID */

  ruid = getuid();

  euid = geteuid();

  (void)suid;

  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,

         "UID is %u (real), %u (effective), unknown (saved)",

         (unsigned)ruid, (unsigned)euid);

#endif /* defined(HAVE_GETRESUID) */

  /* log GIDs */

#ifdef HAVE_GETRESGID

  if (getresgid(&rgid, &egid, &sgid) != 0) {

    log_warn(LD_GENERAL, "Error getting changed GIDs: %s", strerror(errno));

    return -1;

  } else {

    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,

           "GID is %u (real), %u (effective), %u (saved)",

           (unsigned)rgid, (unsigned)egid, (unsigned)sgid);

  }

#else /* !defined(HAVE_GETRESGID) */

  /* getresgid is not present on MacOS X, so we can't get the saved (E)GID */

  rgid = getgid();

  egid = getegid();

  (void)sgid;

  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,

         "GID is %u (real), %u (effective), unknown (saved)",

         (unsigned)rgid, (unsigned)egid);

#endif /* defined(HAVE_GETRESGID) */

  /* log supplementary groups */

  sup_gids_size = 64;

  sup_gids = tor_calloc(64, sizeof(gid_t));

  while ((ngids = getgroups(sup_gids_size, sup_gids)) < 0 &&

         errno == EINVAL &&

         sup_gids_size < NGROUPS_MAX) {

    sup_gids_size *= 2;

    sup_gids = tor_reallocarray(sup_gids, sizeof(gid_t), sup_gids_size);

  }

  if (ngids < 0) {

    log_warn(LD_GENERAL, "Error getting supplementary GIDs: %s",

             strerror(errno));

    tor_free(sup_gids);

    return -1;

  } else {

    int i, retval = 0;

    char *s = NULL;

    smartlist_t *elts = smartlist_new();

    for (i = 0; i<ngids; i++) {

      smartlist_add_asprintf(elts, "%u", (unsigned)sup_gids[i]);

    }

    s = smartlist_join_strings(elts, " ", 0, NULL);

    log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Supplementary groups are: %s",s);

    tor_free(s);

    SMARTLIST_FOREACH(elts, char *, cp, tor_free(cp));

    smartlist_free(elts);

    tor_free(sup_gids);

    return retval;

  }

  return 0;

}

#endif /* !defined(_WIN32) */

/** Return true iff we were compiled with capability support, and capabilities

 * seem to work. **/

int

have_capability_support(void)

{

#ifdef HAVE_LINUX_CAPABILITIES

  cap_t caps = cap_get_proc();

  if (caps == NULL)

    return 0;

  cap_free(caps);

  return 1;

#else /* !defined(HAVE_LINUX_CAPABILITIES) */

  return 0;

#endif /* defined(HAVE_LINUX_CAPABILITIES) */

}

#ifdef HAVE_LINUX_CAPABILITIES

/** Helper. Drop all capabilities but a small set, and set PR_KEEPCAPS as

 * appropriate.

 *

 * If pre_setuid, retain only CAP_NET_BIND_SERVICE, CAP_SETUID, and

 * CAP_SETGID, and use PR_KEEPCAPS to ensure that capabilities persist across

 * setuid().

 *

 * If not pre_setuid, retain only CAP_NET_BIND_SERVICE, and disable

 * PR_KEEPCAPS.

 *

 * Return 0 on success, and -1 on failure.

 */

static int

drop_capabilities(int pre_setuid)

{

  /* We keep these three capabilities, and these only, as we setuid.

   * After we setuid, we drop all but the first. */

  const cap_value_t caplist[] = {

    CAP_NET_BIND_SERVICE, CAP_SETUID, CAP_SETGID

  };

  const char *where = pre_setuid ? "pre-setuid" : "post-setuid";

  const int n_effective = pre_setuid ? 3 : 1;

  const int n_permitted = pre_setuid ? 3 : 1;

  const int n_inheritable = 1;

  const int keepcaps = pre_setuid ? 1 : 0;

  /* Sets whether we keep capabilities across a setuid. */

  if (prctl(PR_SET_KEEPCAPS, keepcaps) < 0) {

    log_warn(LD_CONFIG, "Unable to call prctl() %s: %s",

             where, strerror(errno));

    return -1;

  }

  cap_t caps = cap_get_proc();

  if (!caps) {

    log_warn(LD_CONFIG, "Unable to call cap_get_proc() %s: %s",

             where, strerror(errno));

    return -1;

  }

  cap_clear(caps);

  cap_set_flag(caps, CAP_EFFECTIVE, n_effective, caplist, CAP_SET);

  cap_set_flag(caps, CAP_PERMITTED, n_permitted, caplist, CAP_SET);

  cap_set_flag(caps, CAP_INHERITABLE, n_inheritable, caplist, CAP_SET);

  int r = cap_set_proc(caps);

  cap_free(caps);

  if (r < 0) {

    log_warn(LD_CONFIG, "No permission to set capabilities %s: %s",

             where, strerror(errno));

    return -1;

  }

  return 0;

}

#endif /* defined(HAVE_LINUX_CAPABILITIES) */

/** Call setuid and setgid to run as <b>user</b> and switch to their

 * primary group.  Return 0 on success.  On failure, log and return -1.

 *

 * If SWITCH_ID_KEEP_BINDLOW is set in 'flags', try to use the capability

 * system to retain the abilitity to bind low ports.

 *

 * If SWITCH_ID_WARN_IF_NO_CAPS is set in flags, also warn if we have

 * don't have capability support.

 */

int

switch_id(const char *user, const unsigned flags)

{

#ifndef _WIN32

  const struct passwd *pw = NULL;

  uid_t old_uid;

  gid_t old_gid;

  static int have_already_switched_id = 0;

  const int keep_bindlow = !!(flags & SWITCH_ID_KEEP_BINDLOW);

  const int warn_if_no_caps = !!(flags & SWITCH_ID_WARN_IF_NO_CAPS);

  tor_assert(user);

  if (have_already_switched_id)

    return 0;

  /* Log the initial credential state */

  if (log_credential_status())

    return -1;

  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Changing user and groups");

  /* Get old UID/GID to check if we changed correctly */

  old_uid = getuid();

  old_gid = getgid();

  /* Lookup the user and group information, if we have a problem, bail out. */

  pw = tor_getpwnam(user);

  if (pw == NULL) {

    log_warn(LD_CONFIG, "Error setting configured user: %s not found", user);

    return -1;

  }

#ifdef HAVE_LINUX_CAPABILITIES

  (void) warn_if_no_caps;

  if (keep_bindlow) {

    if (drop_capabilities(1))

      return -1;

  }

#else /* !defined(HAVE_LINUX_CAPABILITIES) */

  (void) keep_bindlow;

  if (warn_if_no_caps) {

    log_warn(LD_CONFIG, "KeepBindCapabilities set, but no capability support "

             "on this system.");

  }

#endif /* defined(HAVE_LINUX_CAPABILITIES) */

  /* Properly switch egid,gid,euid,uid here or bail out */

  if (setgroups(1, &pw->pw_gid)) {

    log_warn(LD_GENERAL, "Error setting groups to gid %d: \"%s\".",

             (int)pw->pw_gid, strerror(errno));

    if (old_uid == pw->pw_uid) {

      log_warn(LD_GENERAL, "Tor is already running as %s.  You do not need "

               "the \"User\" option if you are already running as the user "

               "you want to be.  (If you did not set the User option in your "

               "torrc, check whether it was specified on the command line "

               "by a startup script.)", user);

    } else {

      log_warn(LD_GENERAL, "If you set the \"User\" option, you must start Tor"

               " as root.");

    }

    return -1;

  }

  if (setegid(pw->pw_gid)) {

    log_warn(LD_GENERAL, "Error setting egid to %d: %s",

             (int)pw->pw_gid, strerror(errno));

    return -1;

  }

  if (setgid(pw->pw_gid)) {

    log_warn(LD_GENERAL, "Error setting gid to %d: %s",

             (int)pw->pw_gid, strerror(errno));

    return -1;

  }

  if (setuid(pw->pw_uid)) {

    log_warn(LD_GENERAL, "Error setting configured uid to %s (%d): %s",

             user, (int)pw->pw_uid, strerror(errno));

    return -1;

  }

  if (seteuid(pw->pw_uid)) {

    log_warn(LD_GENERAL, "Error setting configured euid to %s (%d): %s",

             user, (int)pw->pw_uid, strerror(errno));

    return -1;

  }

  /* This is how OpenBSD rolls:

  if (setgroups(1, &pw->pw_gid) || setegid(pw->pw_gid) ||

      setgid(pw->pw_gid) || setuid(pw->pw_uid) || seteuid(pw->pw_uid)) {

      setgid(pw->pw_gid) || seteuid(pw->pw_uid) || setuid(pw->pw_uid)) {

    log_warn(LD_GENERAL, "Error setting configured UID/GID: %s",

    strerror(errno));

    return -1;

  }

  */

  /* We've properly switched egid, gid, euid, uid, and supplementary groups if

   * we're here. */

#ifdef HAVE_LINUX_CAPABILITIES

  if (keep_bindlow) {

    if (drop_capabilities(0))

      return -1;

  }

#endif /* defined(HAVE_LINUX_CAPABILITIES) */

#if !defined(CYGWIN) && !defined(__CYGWIN__)

  /* If we tried to drop privilege to a group/user other than root, attempt to

   * restore root (E)(U|G)ID, and abort if the operation succeeds */

  /* Only check for privilege dropping if we were asked to be non-root */

  if (pw->pw_uid) {

    /* Try changing GID/EGID */

    if (pw->pw_gid != old_gid &&

        (setgid(old_gid) != -1 || setegid(old_gid) != -1)) {

      log_warn(LD_GENERAL, "Was able to restore group credentials even after "

               "switching GID: this means that the setgid code didn't work.");

      return -1;

    }

    /* Try changing UID/EUID */

    if (pw->pw_uid != old_uid &&

        (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) {

      log_warn(LD_GENERAL, "Was able to restore user credentials even after "

               "switching UID: this means that the setuid code didn't work.");

      return -1;

    }

  }

#endif /* !defined(CYGWIN) && !defined(__CYGWIN__) */

  /* Check what really happened */

  if (log_credential_status()) {

    return -1;

  }

  have_already_switched_id = 1; /* mark success so we never try again */

#if defined(__linux__) && defined(HAVE_SYS_PRCTL_H) && \

  defined(HAVE_PRCTL) && defined(PR_SET_DUMPABLE)

  if (pw->pw_uid) {

    /* Re-enable core dumps if we're not running as root. */

    log_info(LD_CONFIG, "Re-enabling coredumps");

    if (prctl(PR_SET_DUMPABLE, 1)) {

      log_warn(LD_CONFIG, "Unable to re-enable coredumps: %s",strerror(errno));

    }

  }

#endif /* defined(__linux__) && defined(HAVE_SYS_PRCTL_H) && ... */

  return 0;

#else /* defined(_WIN32) */

  (void)user;

  (void)flags;

  log_warn(LD_CONFIG, "Switching users is unsupported on your OS.");

  return -1;

#endif /* !defined(_WIN32) */

}