1*664f4763Szrj /* $OpenBSD: uidswap.c,v 1.41 2018/07/18 11:34:04 dtucker Exp $ */ 218de8d7fSPeter Avalos /* 318de8d7fSPeter Avalos * Author: Tatu Ylonen <ylo@cs.hut.fi> 418de8d7fSPeter Avalos * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 518de8d7fSPeter Avalos * All rights reserved 618de8d7fSPeter Avalos * Code for uid-swapping. 718de8d7fSPeter Avalos * 818de8d7fSPeter Avalos * As far as I am concerned, the code I have written for this software 918de8d7fSPeter Avalos * can be used freely for any purpose. Any derived versions of this 1018de8d7fSPeter Avalos * software must be clearly marked as such, and if the derived work is 1118de8d7fSPeter Avalos * incompatible with the protocol description in the RFC file, it must be 1218de8d7fSPeter Avalos * called by a name other than "ssh" or "Secure Shell". 1318de8d7fSPeter Avalos */ 1418de8d7fSPeter Avalos 1518de8d7fSPeter Avalos #include "includes.h" 1618de8d7fSPeter Avalos 1718de8d7fSPeter Avalos #include <errno.h> 1818de8d7fSPeter Avalos #include <pwd.h> 1918de8d7fSPeter Avalos #include <string.h> 2018de8d7fSPeter Avalos #include <unistd.h> 21e9778795SPeter Avalos #include <limits.h> 2218de8d7fSPeter Avalos #include <stdarg.h> 2336e94dc5SPeter Avalos #include <stdlib.h> 2418de8d7fSPeter Avalos 2518de8d7fSPeter Avalos #include <grp.h> 2618de8d7fSPeter Avalos 2718de8d7fSPeter Avalos #include "log.h" 2818de8d7fSPeter Avalos #include "uidswap.h" 2918de8d7fSPeter Avalos #include "xmalloc.h" 3018de8d7fSPeter Avalos 3118de8d7fSPeter Avalos /* 3218de8d7fSPeter Avalos * Note: all these functions must work in all of the following cases: 3318de8d7fSPeter Avalos * 1. euid=0, ruid=0 3418de8d7fSPeter Avalos * 2. euid=0, ruid!=0 3518de8d7fSPeter Avalos * 3. euid!=0, ruid!=0 3618de8d7fSPeter Avalos * Additionally, they must work regardless of whether the system has 3718de8d7fSPeter Avalos * POSIX saved uids or not. 3818de8d7fSPeter Avalos */ 3918de8d7fSPeter Avalos 4018de8d7fSPeter Avalos #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 4118de8d7fSPeter Avalos /* Lets assume that posix saved ids also work with seteuid, even though that 4218de8d7fSPeter Avalos is not part of the posix specification. */ 4318de8d7fSPeter Avalos #define SAVED_IDS_WORK_WITH_SETEUID 4418de8d7fSPeter Avalos /* Saved effective uid. */ 4518de8d7fSPeter Avalos static uid_t saved_euid = 0; 4618de8d7fSPeter Avalos static gid_t saved_egid = 0; 4718de8d7fSPeter Avalos #endif 4818de8d7fSPeter Avalos 4918de8d7fSPeter Avalos /* Saved effective uid. */ 5018de8d7fSPeter Avalos static int privileged = 0; 5118de8d7fSPeter Avalos static int temporarily_use_uid_effective = 0; 52*664f4763Szrj static uid_t user_groups_uid; 5318de8d7fSPeter Avalos static gid_t *saved_egroups = NULL, *user_groups = NULL; 5418de8d7fSPeter Avalos static int saved_egroupslen = -1, user_groupslen = -1; 5518de8d7fSPeter Avalos 5618de8d7fSPeter Avalos /* 5718de8d7fSPeter Avalos * Temporarily changes to the given uid. If the effective user 5818de8d7fSPeter Avalos * id is not root, this does nothing. This call cannot be nested. 5918de8d7fSPeter Avalos */ 6018de8d7fSPeter Avalos void 6118de8d7fSPeter Avalos temporarily_use_uid(struct passwd *pw) 6218de8d7fSPeter Avalos { 6318de8d7fSPeter Avalos /* Save the current euid, and egroups. */ 6418de8d7fSPeter Avalos #ifdef SAVED_IDS_WORK_WITH_SETEUID 6518de8d7fSPeter Avalos saved_euid = geteuid(); 6618de8d7fSPeter Avalos saved_egid = getegid(); 6718de8d7fSPeter Avalos debug("temporarily_use_uid: %u/%u (e=%u/%u)", 6818de8d7fSPeter Avalos (u_int)pw->pw_uid, (u_int)pw->pw_gid, 6918de8d7fSPeter Avalos (u_int)saved_euid, (u_int)saved_egid); 7018de8d7fSPeter Avalos #ifndef HAVE_CYGWIN 7118de8d7fSPeter Avalos if (saved_euid != 0) { 7218de8d7fSPeter Avalos privileged = 0; 7318de8d7fSPeter Avalos return; 7418de8d7fSPeter Avalos } 7518de8d7fSPeter Avalos #endif 7618de8d7fSPeter Avalos #else 7718de8d7fSPeter Avalos if (geteuid() != 0) { 7818de8d7fSPeter Avalos privileged = 0; 7918de8d7fSPeter Avalos return; 8018de8d7fSPeter Avalos } 8118de8d7fSPeter Avalos #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 8218de8d7fSPeter Avalos 8318de8d7fSPeter Avalos privileged = 1; 8418de8d7fSPeter Avalos temporarily_use_uid_effective = 1; 8518de8d7fSPeter Avalos 8618de8d7fSPeter Avalos saved_egroupslen = getgroups(0, NULL); 8718de8d7fSPeter Avalos if (saved_egroupslen < 0) 8818de8d7fSPeter Avalos fatal("getgroups: %.100s", strerror(errno)); 8918de8d7fSPeter Avalos if (saved_egroupslen > 0) { 90e9778795SPeter Avalos saved_egroups = xreallocarray(saved_egroups, 9118de8d7fSPeter Avalos saved_egroupslen, sizeof(gid_t)); 9218de8d7fSPeter Avalos if (getgroups(saved_egroupslen, saved_egroups) < 0) 9318de8d7fSPeter Avalos fatal("getgroups: %.100s", strerror(errno)); 9418de8d7fSPeter Avalos } else { /* saved_egroupslen == 0 */ 9536e94dc5SPeter Avalos free(saved_egroups); 96*664f4763Szrj saved_egroups = NULL; 9718de8d7fSPeter Avalos } 9818de8d7fSPeter Avalos 9918de8d7fSPeter Avalos /* set and save the user's groups */ 100*664f4763Szrj if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) { 10118de8d7fSPeter Avalos if (initgroups(pw->pw_name, pw->pw_gid) < 0) 10218de8d7fSPeter Avalos fatal("initgroups: %s: %.100s", pw->pw_name, 10318de8d7fSPeter Avalos strerror(errno)); 10418de8d7fSPeter Avalos 10518de8d7fSPeter Avalos user_groupslen = getgroups(0, NULL); 10618de8d7fSPeter Avalos if (user_groupslen < 0) 10718de8d7fSPeter Avalos fatal("getgroups: %.100s", strerror(errno)); 10818de8d7fSPeter Avalos if (user_groupslen > 0) { 109e9778795SPeter Avalos user_groups = xreallocarray(user_groups, 11018de8d7fSPeter Avalos user_groupslen, sizeof(gid_t)); 11118de8d7fSPeter Avalos if (getgroups(user_groupslen, user_groups) < 0) 11218de8d7fSPeter Avalos fatal("getgroups: %.100s", strerror(errno)); 11318de8d7fSPeter Avalos } else { /* user_groupslen == 0 */ 11436e94dc5SPeter Avalos free(user_groups); 115*664f4763Szrj user_groups = NULL; 11618de8d7fSPeter Avalos } 117*664f4763Szrj user_groups_uid = pw->pw_uid; 11818de8d7fSPeter Avalos } 11918de8d7fSPeter Avalos /* Set the effective uid to the given (unprivileged) uid. */ 12018de8d7fSPeter Avalos if (setgroups(user_groupslen, user_groups) < 0) 12118de8d7fSPeter Avalos fatal("setgroups: %.100s", strerror(errno)); 12218de8d7fSPeter Avalos #ifndef SAVED_IDS_WORK_WITH_SETEUID 12318de8d7fSPeter Avalos /* Propagate the privileged gid to all of our gids. */ 12418de8d7fSPeter Avalos if (setgid(getegid()) < 0) 12518de8d7fSPeter Avalos debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 12618de8d7fSPeter Avalos /* Propagate the privileged uid to all of our uids. */ 12718de8d7fSPeter Avalos if (setuid(geteuid()) < 0) 12818de8d7fSPeter Avalos debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 12918de8d7fSPeter Avalos #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 13018de8d7fSPeter Avalos if (setegid(pw->pw_gid) < 0) 13118de8d7fSPeter Avalos fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 13218de8d7fSPeter Avalos strerror(errno)); 13318de8d7fSPeter Avalos if (seteuid(pw->pw_uid) == -1) 13418de8d7fSPeter Avalos fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 13518de8d7fSPeter Avalos strerror(errno)); 13618de8d7fSPeter Avalos } 13718de8d7fSPeter Avalos 13818de8d7fSPeter Avalos /* 13918de8d7fSPeter Avalos * Restores to the original (privileged) uid. 14018de8d7fSPeter Avalos */ 14118de8d7fSPeter Avalos void 14218de8d7fSPeter Avalos restore_uid(void) 14318de8d7fSPeter Avalos { 14418de8d7fSPeter Avalos /* it's a no-op unless privileged */ 14518de8d7fSPeter Avalos if (!privileged) { 14618de8d7fSPeter Avalos debug("restore_uid: (unprivileged)"); 14718de8d7fSPeter Avalos return; 14818de8d7fSPeter Avalos } 14918de8d7fSPeter Avalos if (!temporarily_use_uid_effective) 15018de8d7fSPeter Avalos fatal("restore_uid: temporarily_use_uid not effective"); 15118de8d7fSPeter Avalos 15218de8d7fSPeter Avalos #ifdef SAVED_IDS_WORK_WITH_SETEUID 15318de8d7fSPeter Avalos debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 15418de8d7fSPeter Avalos /* Set the effective uid back to the saved privileged uid. */ 15518de8d7fSPeter Avalos if (seteuid(saved_euid) < 0) 15618de8d7fSPeter Avalos fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 15718de8d7fSPeter Avalos if (setegid(saved_egid) < 0) 15818de8d7fSPeter Avalos fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 15918de8d7fSPeter Avalos #else /* SAVED_IDS_WORK_WITH_SETEUID */ 16018de8d7fSPeter Avalos /* 16118de8d7fSPeter Avalos * We are unable to restore the real uid to its unprivileged value. 16218de8d7fSPeter Avalos * Propagate the real uid (usually more privileged) to effective uid 16318de8d7fSPeter Avalos * as well. 16418de8d7fSPeter Avalos */ 16518de8d7fSPeter Avalos setuid(getuid()); 16618de8d7fSPeter Avalos setgid(getgid()); 16718de8d7fSPeter Avalos #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 16818de8d7fSPeter Avalos 16918de8d7fSPeter Avalos if (setgroups(saved_egroupslen, saved_egroups) < 0) 17018de8d7fSPeter Avalos fatal("setgroups: %.100s", strerror(errno)); 17118de8d7fSPeter Avalos temporarily_use_uid_effective = 0; 17218de8d7fSPeter Avalos } 17318de8d7fSPeter Avalos 17418de8d7fSPeter Avalos /* 17518de8d7fSPeter Avalos * Permanently sets all uids to the given uid. This cannot be 17618de8d7fSPeter Avalos * called while temporarily_use_uid is effective. 17718de8d7fSPeter Avalos */ 17818de8d7fSPeter Avalos void 17918de8d7fSPeter Avalos permanently_set_uid(struct passwd *pw) 18018de8d7fSPeter Avalos { 181e9778795SPeter Avalos #ifndef NO_UID_RESTORATION_TEST 18218de8d7fSPeter Avalos uid_t old_uid = getuid(); 18318de8d7fSPeter Avalos gid_t old_gid = getgid(); 18436e94dc5SPeter Avalos #endif 18518de8d7fSPeter Avalos 18618de8d7fSPeter Avalos if (pw == NULL) 18718de8d7fSPeter Avalos fatal("permanently_set_uid: no user given"); 18818de8d7fSPeter Avalos if (temporarily_use_uid_effective) 18918de8d7fSPeter Avalos fatal("permanently_set_uid: temporarily_use_uid effective"); 19018de8d7fSPeter Avalos debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 19118de8d7fSPeter Avalos (u_int)pw->pw_gid); 19218de8d7fSPeter Avalos 19318de8d7fSPeter Avalos if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 19418de8d7fSPeter Avalos fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 19518de8d7fSPeter Avalos 196cb5eb4f1SPeter Avalos #ifdef __APPLE__ 197cb5eb4f1SPeter Avalos /* 198cb5eb4f1SPeter Avalos * OS X requires initgroups after setgid to opt back into 199cb5eb4f1SPeter Avalos * memberd support for >16 supplemental groups. 200cb5eb4f1SPeter Avalos */ 201cb5eb4f1SPeter Avalos if (initgroups(pw->pw_name, pw->pw_gid) < 0) 202cb5eb4f1SPeter Avalos fatal("initgroups %.100s %u: %.100s", 203cb5eb4f1SPeter Avalos pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 204cb5eb4f1SPeter Avalos #endif 205cb5eb4f1SPeter Avalos 20618de8d7fSPeter Avalos if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 20718de8d7fSPeter Avalos fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 20818de8d7fSPeter Avalos 209e9778795SPeter Avalos #ifndef NO_UID_RESTORATION_TEST 21018de8d7fSPeter Avalos /* Try restoration of GID if changed (test clearing of saved gid) */ 21118de8d7fSPeter Avalos if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 21218de8d7fSPeter Avalos (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 21318de8d7fSPeter Avalos fatal("%s: was able to restore old [e]gid", __func__); 21418de8d7fSPeter Avalos #endif 21518de8d7fSPeter Avalos 21618de8d7fSPeter Avalos /* Verify GID drop was successful */ 21718de8d7fSPeter Avalos if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 21818de8d7fSPeter Avalos fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 21918de8d7fSPeter Avalos __func__, (u_int)getgid(), (u_int)getegid(), 22018de8d7fSPeter Avalos (u_int)pw->pw_gid); 22118de8d7fSPeter Avalos } 22218de8d7fSPeter Avalos 223e9778795SPeter Avalos #ifndef NO_UID_RESTORATION_TEST 22418de8d7fSPeter Avalos /* Try restoration of UID if changed (test clearing of saved uid) */ 22518de8d7fSPeter Avalos if (old_uid != pw->pw_uid && 22618de8d7fSPeter Avalos (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 22718de8d7fSPeter Avalos fatal("%s: was able to restore old [e]uid", __func__); 22818de8d7fSPeter Avalos #endif 22918de8d7fSPeter Avalos 23018de8d7fSPeter Avalos /* Verify UID drop was successful */ 23118de8d7fSPeter Avalos if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 23218de8d7fSPeter Avalos fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 23318de8d7fSPeter Avalos __func__, (u_int)getuid(), (u_int)geteuid(), 23418de8d7fSPeter Avalos (u_int)pw->pw_uid); 23518de8d7fSPeter Avalos } 23618de8d7fSPeter Avalos } 237