uidswap.c - third_party/openssh-portable - Git at Google

 /* $OpenBSD: uidswap.c,v 1.41 2018/07/18 11:34:04 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
  * Code for uid-swapping.
  *
  * 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".
  */

 #include "includes.h"

 #include <errno.h>
 #include <pwd.h>
 #include <string.h>
 #include <unistd.h>
 #include <limits.h>
 #include <stdarg.h>
 #include <stdlib.h>

 #include <grp.h>

 #include "log.h"
 #include "uidswap.h"
 #include "xmalloc.h"

 /*
  * Note: all these functions must work in all of the following cases:
  *    1. euid=0, ruid=0
  *    2. euid=0, ruid!=0
  *    3. euid!=0, ruid!=0
  * Additionally, they must work regardless of whether the system has
  * POSIX saved uids or not.
  */

 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
 /* Lets assume that posix saved ids also work with seteuid, even though that
    is not part of the posix specification. */
 #define SAVED_IDS_WORK_WITH_SETEUID
 /* Saved effective uid. */
 static uid_t 	saved_euid = 0;
 static gid_t	saved_egid = 0;
 #endif

 /* Saved effective uid. */
 static int	privileged = 0;
 static int	temporarily_use_uid_effective = 0;
 static uid_t	user_groups_uid;
 static gid_t	*saved_egroups = NULL, *user_groups = NULL;
 static int	saved_egroupslen = -1, user_groupslen = -1;

 /*
  * Temporarily changes to the given uid.  If the effective user
  * id is not root, this does nothing.  This call cannot be nested.
  */
 void
 temporarily_use_uid(struct passwd *pw)
 {
 	/* Save the current euid, and egroups. */
 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 	saved_euid = geteuid();
 	saved_egid = getegid();
 	debug("temporarily_use_uid: %u/%u (e=%u/%u)",
 	    (u_int)pw->pw_uid, (u_int)pw->pw_gid,
 	    (u_int)saved_euid, (u_int)saved_egid);
 #ifndef HAVE_CYGWIN
 	if (saved_euid != 0) {
 		privileged = 0;
 		return;
 	}
 #endif
 #else
 	if (geteuid() != 0) {
 		privileged = 0;
 		return;
 	}
 #endif /* SAVED_IDS_WORK_WITH_SETEUID */

 	privileged = 1;
 	temporarily_use_uid_effective = 1;

 	saved_egroupslen = getgroups(0, NULL);
 	if (saved_egroupslen < 0)
 		fatal("getgroups: %.100s", strerror(errno));
 	if (saved_egroupslen > 0) {
 		saved_egroups = xreallocarray(saved_egroups,
 		    saved_egroupslen, sizeof(gid_t));
 		if (getgroups(saved_egroupslen, saved_egroups) < 0)
 			fatal("getgroups: %.100s", strerror(errno));
 	} else { /* saved_egroupslen == 0 */
 		free(saved_egroups);
 		saved_egroups = NULL;
 	}

 	/* set and save the user's groups */
 	if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) {
 		if (initgroups(pw->pw_name, pw->pw_gid) < 0)
 			fatal("initgroups: %s: %.100s", pw->pw_name,
 			    strerror(errno));

 		user_groupslen = getgroups(0, NULL);
 		if (user_groupslen < 0)
 			fatal("getgroups: %.100s", strerror(errno));
 		if (user_groupslen > 0) {
 			user_groups = xreallocarray(user_groups,
 			    user_groupslen, sizeof(gid_t));
 			if (getgroups(user_groupslen, user_groups) < 0)
 				fatal("getgroups: %.100s", strerror(errno));
 		} else { /* user_groupslen == 0 */
 			free(user_groups);
 			user_groups = NULL;
 		}
 		user_groups_uid = pw->pw_uid;
 	}
 	/* Set the effective uid to the given (unprivileged) uid. */
 	if (setgroups(user_groupslen, user_groups) < 0)
 		fatal("setgroups: %.100s", strerror(errno));
 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 	/* Propagate the privileged gid to all of our gids. */
 	if (setgid(getegid()) < 0)
 		debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 	/* Propagate the privileged uid to all of our uids. */
 	if (setuid(geteuid()) < 0)
 		debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 	if (setegid(pw->pw_gid) < 0)
 		fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 		    strerror(errno));
 	if (seteuid(pw->pw_uid) == -1)
 		fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 		    strerror(errno));
 }

 /*
  * Restores to the original (privileged) uid.
  */
 void
 restore_uid(void)
 {
 	/* it's a no-op unless privileged */
 	if (!privileged) {
 		debug("restore_uid: (unprivileged)");
 		return;
 	}
 	if (!temporarily_use_uid_effective)
 		fatal("restore_uid: temporarily_use_uid not effective");

 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 	debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 	/* Set the effective uid back to the saved privileged uid. */
 	if (seteuid(saved_euid) < 0)
 		fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 	if (setegid(saved_egid) < 0)
 		fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 	/*
 	 * We are unable to restore the real uid to its unprivileged value.
 	 * Propagate the real uid (usually more privileged) to effective uid
 	 * as well.
 	 */
 	setuid(getuid());
 	setgid(getgid());
 #endif /* SAVED_IDS_WORK_WITH_SETEUID */

 	if (setgroups(saved_egroupslen, saved_egroups) < 0)
 		fatal("setgroups: %.100s", strerror(errno));
 	temporarily_use_uid_effective = 0;
 }

 /*
  * Permanently sets all uids to the given uid.  This cannot be
  * called while temporarily_use_uid is effective.
  */
 void
 permanently_set_uid(struct passwd *pw)
 {
 #ifndef NO_UID_RESTORATION_TEST
 	uid_t old_uid = getuid();
 	gid_t old_gid = getgid();
 #endif

 	if (pw == NULL)
 		fatal("permanently_set_uid: no user given");
 	if (temporarily_use_uid_effective)
 		fatal("permanently_set_uid: temporarily_use_uid effective");
 	debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 	    (u_int)pw->pw_gid);

 	if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 		fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));

 #ifdef __APPLE__
 	/*
 	 * OS X requires initgroups after setgid to opt back into
 	 * memberd support for >16 supplemental groups.
 	 */
 	if (initgroups(pw->pw_name, pw->pw_gid) < 0)
 		fatal("initgroups %.100s %u: %.100s",
 		    pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
 #endif

 	if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 		fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));

 #ifndef NO_UID_RESTORATION_TEST
 	/* Try restoration of GID if changed (test clearing of saved gid) */
 	if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 	    (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 		fatal("%s: was able to restore old [e]gid", __func__);
 #endif

 	/* Verify GID drop was successful */
 	if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 		fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 		    __func__, (u_int)getgid(), (u_int)getegid(),
 		    (u_int)pw->pw_gid);
 	}

 #ifndef NO_UID_RESTORATION_TEST
 	/* Try restoration of UID if changed (test clearing of saved uid) */
 	if (old_uid != pw->pw_uid &&
 	    (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 		fatal("%s: was able to restore old [e]uid", __func__);
 #endif

 	/* Verify UID drop was successful */
 	if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 		fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 		    __func__, (u_int)getuid(), (u_int)geteuid(),
 		    (u_int)pw->pw_uid);
 	}
 }
	/* $OpenBSD: uidswap.c,v 1.41 2018/07/18 11:34:04 dtucker Exp $ */
	/*
	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	* Code for uid-swapping.
	*
	* 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".
	*/

	#include "includes.h"

	#include <errno.h>
	#include <pwd.h>
	#include <string.h>
	#include <unistd.h>
	#include <limits.h>
	#include <stdarg.h>
	#include <stdlib.h>

	#include <grp.h>

	#include "log.h"
	#include "uidswap.h"
	#include "xmalloc.h"

	/*
	* Note: all these functions must work in all of the following cases:
	* 1. euid=0, ruid=0
	* 2. euid=0, ruid!=0
	* 3. euid!=0, ruid!=0
	* Additionally, they must work regardless of whether the system has
	* POSIX saved uids or not.
	*/

	#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
	/* Lets assume that posix saved ids also work with seteuid, even though that
	is not part of the posix specification. */
	#define SAVED_IDS_WORK_WITH_SETEUID
	/* Saved effective uid. */
	static uid_t saved_euid = 0;
	static gid_t saved_egid = 0;
	#endif

	/* Saved effective uid. */
	static int privileged = 0;
	static int temporarily_use_uid_effective = 0;
	static uid_t user_groups_uid;
	static gid_t saved_egroups = NULL, user_groups = NULL;
	static int saved_egroupslen = -1, user_groupslen = -1;

	/*
	* Temporarily changes to the given uid. If the effective user
	* id is not root, this does nothing. This call cannot be nested.
	*/
	void
	temporarily_use_uid(struct passwd *pw)
	{
	/* Save the current euid, and egroups. */
	#ifdef SAVED_IDS_WORK_WITH_SETEUID
	saved_euid = geteuid();
	saved_egid = getegid();
	debug("temporarily_use_uid: %u/%u (e=%u/%u)",
	(u_int)pw->pw_uid, (u_int)pw->pw_gid,
	(u_int)saved_euid, (u_int)saved_egid);
	#ifndef HAVE_CYGWIN
	if (saved_euid != 0) {
	privileged = 0;
	return;
	}
	#endif
	#else
	if (geteuid() != 0) {
	privileged = 0;
	return;
	}
	#endif /* SAVED_IDS_WORK_WITH_SETEUID */

	privileged = 1;
	temporarily_use_uid_effective = 1;

	saved_egroupslen = getgroups(0, NULL);
	if (saved_egroupslen < 0)
	fatal("getgroups: %.100s", strerror(errno));
	if (saved_egroupslen > 0) {
	saved_egroups = xreallocarray(saved_egroups,
	saved_egroupslen, sizeof(gid_t));
	if (getgroups(saved_egroupslen, saved_egroups) < 0)
	fatal("getgroups: %.100s", strerror(errno));
	} else { /* saved_egroupslen == 0 */
	free(saved_egroups);
	saved_egroups = NULL;
	}

	/* set and save the user's groups */
	if (user_groupslen == -1 \|\| user_groups_uid != pw->pw_uid) {
	if (initgroups(pw->pw_name, pw->pw_gid) < 0)
	fatal("initgroups: %s: %.100s", pw->pw_name,
	strerror(errno));

	user_groupslen = getgroups(0, NULL);
	if (user_groupslen < 0)
	fatal("getgroups: %.100s", strerror(errno));
	if (user_groupslen > 0) {
	user_groups = xreallocarray(user_groups,
	user_groupslen, sizeof(gid_t));
	if (getgroups(user_groupslen, user_groups) < 0)
	fatal("getgroups: %.100s", strerror(errno));
	} else { /* user_groupslen == 0 */
	free(user_groups);
	user_groups = NULL;
	}
	user_groups_uid = pw->pw_uid;
	}
	/* Set the effective uid to the given (unprivileged) uid. */
	if (setgroups(user_groupslen, user_groups) < 0)
	fatal("setgroups: %.100s", strerror(errno));
	#ifndef SAVED_IDS_WORK_WITH_SETEUID
	/* Propagate the privileged gid to all of our gids. */
	if (setgid(getegid()) < 0)
	debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
	/* Propagate the privileged uid to all of our uids. */
	if (setuid(geteuid()) < 0)
	debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
	#endif /* SAVED_IDS_WORK_WITH_SETEUID */
	if (setegid(pw->pw_gid) < 0)
	fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
	strerror(errno));
	if (seteuid(pw->pw_uid) == -1)
	fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
	strerror(errno));
	}

	/*
	* Restores to the original (privileged) uid.
	*/
	void
	restore_uid(void)
	{
	/* it's a no-op unless privileged */
	if (!privileged) {
	debug("restore_uid: (unprivileged)");
	return;
	}
	if (!temporarily_use_uid_effective)
	fatal("restore_uid: temporarily_use_uid not effective");

	#ifdef SAVED_IDS_WORK_WITH_SETEUID
	debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
	/* Set the effective uid back to the saved privileged uid. */
	if (seteuid(saved_euid) < 0)
	fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
	if (setegid(saved_egid) < 0)
	fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
	#else /* SAVED_IDS_WORK_WITH_SETEUID */
	/*
	* We are unable to restore the real uid to its unprivileged value.
	* Propagate the real uid (usually more privileged) to effective uid
	* as well.
	*/
	setuid(getuid());
	setgid(getgid());
	#endif /* SAVED_IDS_WORK_WITH_SETEUID */

	if (setgroups(saved_egroupslen, saved_egroups) < 0)
	fatal("setgroups: %.100s", strerror(errno));
	temporarily_use_uid_effective = 0;
	}

	/*
	* Permanently sets all uids to the given uid. This cannot be
	* called while temporarily_use_uid is effective.
	*/
	void
	permanently_set_uid(struct passwd *pw)
	{
	#ifndef NO_UID_RESTORATION_TEST
	uid_t old_uid = getuid();
	gid_t old_gid = getgid();
	#endif

	if (pw == NULL)
	fatal("permanently_set_uid: no user given");
	if (temporarily_use_uid_effective)
	fatal("permanently_set_uid: temporarily_use_uid effective");
	debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
	(u_int)pw->pw_gid);

	if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
	fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));

	#ifdef __APPLE__
	/*
	* OS X requires initgroups after setgid to opt back into
	* memberd support for >16 supplemental groups.
	*/
	if (initgroups(pw->pw_name, pw->pw_gid) < 0)
	fatal("initgroups %.100s %u: %.100s",
	pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
	#endif

	if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
	fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));

	#ifndef NO_UID_RESTORATION_TEST
	/* Try restoration of GID if changed (test clearing of saved gid) */
	if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
	(setgid(old_gid) != -1 \|\| setegid(old_gid) != -1))
	fatal("%s: was able to restore old [e]gid", __func__);
	#endif

	/* Verify GID drop was successful */
	if (getgid() != pw->pw_gid \|\| getegid() != pw->pw_gid) {
	fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
	__func__, (u_int)getgid(), (u_int)getegid(),
	(u_int)pw->pw_gid);
	}

	#ifndef NO_UID_RESTORATION_TEST
	/* Try restoration of UID if changed (test clearing of saved uid) */
	if (old_uid != pw->pw_uid &&
	(setuid(old_uid) != -1 \|\| seteuid(old_uid) != -1))
	fatal("%s: was able to restore old [e]uid", __func__);
	#endif

	/* Verify UID drop was successful */
	if (getuid() != pw->pw_uid \|\| geteuid() != pw->pw_uid) {
	fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
	__func__, (u_int)getuid(), (u_int)geteuid(),
	(u_int)pw->pw_uid);
	}
	}