239 lines
7.3 KiB
C
239 lines
7.3 KiB
C
/* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 deraadt Exp $ */
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/*
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* Author: Tatu Ylonen <ylo@cs.hut.fi>
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* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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* All rights reserved
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* Code for uid-swapping.
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*
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* As far as I am concerned, the code I have written for this software
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* can be used freely for any purpose. Any derived versions of this
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* software must be clearly marked as such, and if the derived work is
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* incompatible with the protocol description in the RFC file, it must be
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* called by a name other than "ssh" or "Secure Shell".
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*/
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#include "includes.h"
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#include <errno.h>
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#include <pwd.h>
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#include <string.h>
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#include <unistd.h>
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#include <limits.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <grp.h>
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#include "log.h"
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#include "uidswap.h"
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#include "xmalloc.h"
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/*
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* Note: all these functions must work in all of the following cases:
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* 1. euid=0, ruid=0
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* 2. euid=0, ruid!=0
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* 3. euid!=0, ruid!=0
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* Additionally, they must work regardless of whether the system has
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* POSIX saved uids or not.
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*/
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#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
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/* Lets assume that posix saved ids also work with seteuid, even though that
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is not part of the posix specification. */
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#define SAVED_IDS_WORK_WITH_SETEUID
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/* Saved effective uid. */
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static uid_t saved_euid = 0;
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static gid_t saved_egid = 0;
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#endif
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/* Saved effective uid. */
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static int privileged = 0;
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static int temporarily_use_uid_effective = 0;
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static uid_t user_groups_uid;
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static gid_t *saved_egroups = NULL, *user_groups = NULL;
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static int saved_egroupslen = -1, user_groupslen = -1;
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/*
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* Temporarily changes to the given uid. If the effective user
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* id is not root, this does nothing. This call cannot be nested.
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*/
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void
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temporarily_use_uid(struct passwd *pw)
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{
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/* Save the current euid, and egroups. */
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#ifdef SAVED_IDS_WORK_WITH_SETEUID
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saved_euid = geteuid();
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saved_egid = getegid();
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debug("temporarily_use_uid: %u/%u (e=%u/%u)",
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(u_int)pw->pw_uid, (u_int)pw->pw_gid,
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(u_int)saved_euid, (u_int)saved_egid);
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#ifndef HAVE_CYGWIN
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if (saved_euid != 0) {
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privileged = 0;
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return;
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}
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#endif
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#else
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if (geteuid() != 0) {
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privileged = 0;
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return;
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}
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#endif /* SAVED_IDS_WORK_WITH_SETEUID */
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privileged = 1;
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temporarily_use_uid_effective = 1;
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saved_egroupslen = getgroups(0, NULL);
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if (saved_egroupslen == -1)
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fatal("getgroups: %.100s", strerror(errno));
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if (saved_egroupslen > 0) {
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saved_egroups = xreallocarray(saved_egroups,
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saved_egroupslen, sizeof(gid_t));
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if (getgroups(saved_egroupslen, saved_egroups) == -1)
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fatal("getgroups: %.100s", strerror(errno));
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} else { /* saved_egroupslen == 0 */
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free(saved_egroups);
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saved_egroups = NULL;
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}
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/* set and save the user's groups */
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if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) {
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if (initgroups(pw->pw_name, pw->pw_gid) == -1)
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fatal("initgroups: %s: %.100s", pw->pw_name,
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strerror(errno));
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user_groupslen = getgroups(0, NULL);
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if (user_groupslen == -1)
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fatal("getgroups: %.100s", strerror(errno));
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if (user_groupslen > 0) {
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user_groups = xreallocarray(user_groups,
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user_groupslen, sizeof(gid_t));
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if (getgroups(user_groupslen, user_groups) == -1)
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fatal("getgroups: %.100s", strerror(errno));
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} else { /* user_groupslen == 0 */
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free(user_groups);
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user_groups = NULL;
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}
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user_groups_uid = pw->pw_uid;
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}
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/* Set the effective uid to the given (unprivileged) uid. */
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if (setgroups(user_groupslen, user_groups) == -1)
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fatal("setgroups: %.100s", strerror(errno));
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#ifndef SAVED_IDS_WORK_WITH_SETEUID
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/* Propagate the privileged gid to all of our gids. */
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if (setgid(getegid()) == -1)
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debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
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/* Propagate the privileged uid to all of our uids. */
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if (setuid(geteuid()) == -1)
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debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
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#endif /* SAVED_IDS_WORK_WITH_SETEUID */
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if (setegid(pw->pw_gid) == -1)
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fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
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strerror(errno));
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if (seteuid(pw->pw_uid) == -1)
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fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
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strerror(errno));
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}
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/*
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* Restores to the original (privileged) uid.
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*/
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void
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restore_uid(void)
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{
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/* it's a no-op unless privileged */
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if (!privileged) {
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debug("restore_uid: (unprivileged)");
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return;
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}
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if (!temporarily_use_uid_effective)
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fatal("restore_uid: temporarily_use_uid not effective");
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#ifdef SAVED_IDS_WORK_WITH_SETEUID
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debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
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/* Set the effective uid back to the saved privileged uid. */
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if (seteuid(saved_euid) == -1)
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fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
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if (setegid(saved_egid) == -1)
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fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
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#else /* SAVED_IDS_WORK_WITH_SETEUID */
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/*
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* We are unable to restore the real uid to its unprivileged value.
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* Propagate the real uid (usually more privileged) to effective uid
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* as well.
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*/
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if (setuid(getuid()) == -1)
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fatal("%s: setuid failed: %s", __func__, strerror(errno));
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if (setgid(getgid()) == -1)
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fatal("%s: setgid failed: %s", __func__, strerror(errno));
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#endif /* SAVED_IDS_WORK_WITH_SETEUID */
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if (setgroups(saved_egroupslen, saved_egroups) == -1)
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fatal("setgroups: %.100s", strerror(errno));
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temporarily_use_uid_effective = 0;
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}
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/*
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* Permanently sets all uids to the given uid. This cannot be
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* called while temporarily_use_uid is effective.
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*/
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void
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permanently_set_uid(struct passwd *pw)
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{
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#ifndef NO_UID_RESTORATION_TEST
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uid_t old_uid = getuid();
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gid_t old_gid = getgid();
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#endif
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if (pw == NULL)
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fatal("permanently_set_uid: no user given");
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if (temporarily_use_uid_effective)
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fatal("permanently_set_uid: temporarily_use_uid effective");
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debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
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(u_int)pw->pw_gid);
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if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1)
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fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
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#ifdef __APPLE__
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/*
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* OS X requires initgroups after setgid to opt back into
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* memberd support for >16 supplemental groups.
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*/
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if (initgroups(pw->pw_name, pw->pw_gid) == -1)
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fatal("initgroups %.100s %u: %.100s",
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pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
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#endif
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if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1)
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fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
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#ifndef NO_UID_RESTORATION_TEST
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/* Try restoration of GID if changed (test clearing of saved gid) */
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if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
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(setgid(old_gid) != -1 || setegid(old_gid) != -1))
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fatal("%s: was able to restore old [e]gid", __func__);
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#endif
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/* Verify GID drop was successful */
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if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
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fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
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__func__, (u_int)getgid(), (u_int)getegid(),
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(u_int)pw->pw_gid);
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}
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#ifndef NO_UID_RESTORATION_TEST
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/* Try restoration of UID if changed (test clearing of saved uid) */
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if (old_uid != pw->pw_uid &&
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(setuid(old_uid) != -1 || seteuid(old_uid) != -1))
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fatal("%s: was able to restore old [e]uid", __func__);
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#endif
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/* Verify UID drop was successful */
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if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
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fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
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__func__, (u_int)getuid(), (u_int)geteuid(),
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(u_int)pw->pw_uid);
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}
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}
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