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/* $OpenBSD: uidswap.c,v 1.40 2018/06/15 07:01:11 djm 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));
}
void
permanently_drop_suid(uid_t uid)
{
#ifndef NO_UID_RESTORATION_TEST
uid_t old_uid = getuid();
#endif
debug("permanently_drop_suid: %u", (u_int)uid);
if (setresuid(uid, uid, uid) < 0)
fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
#ifndef NO_UID_RESTORATION_TEST
/*
* Try restoration of UID if changed (test clearing of saved uid).
*
* Note that we don't do this on Cygwin, or on Solaris-based platforms
* where fine-grained privileges are available (the user might be
* deliberately allowed the right to setuid back to root).
*/
if (old_uid != 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() != uid || geteuid() != uid) {
fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
__func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
}
}
/*
* 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);
}
}
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