diff options
Diffstat (limited to 'uidswap.c')
| -rw-r--r-- | uidswap.c | 236 |
1 files changed, 236 insertions, 0 deletions
diff --git a/uidswap.c b/uidswap.c new file mode 100644 index 0000000..49f76d8 --- /dev/null +++ b/uidswap.c @@ -0,0 +1,236 @@ +/* $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); + } +} |