uidswap.c revision 192595
136285Sbrian/* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */ 236285Sbrian/* 336285Sbrian * Author: Tatu Ylonen <ylo@cs.hut.fi> 436285Sbrian * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 536285Sbrian * All rights reserved 636285Sbrian * Code for uid-swapping. 736285Sbrian * 836285Sbrian * As far as I am concerned, the code I have written for this software 936285Sbrian * can be used freely for any purpose. Any derived versions of this 1036285Sbrian * software must be clearly marked as such, and if the derived work is 1136285Sbrian * incompatible with the protocol description in the RFC file, it must be 1236285Sbrian * called by a name other than "ssh" or "Secure Shell". 1336285Sbrian */ 1436285Sbrian 1536285Sbrian#include "includes.h" 1636285Sbrian 1736285Sbrian#include <sys/param.h> 1836285Sbrian#include <errno.h> 1936285Sbrian#include <pwd.h> 2036285Sbrian#include <string.h> 2136285Sbrian#include <unistd.h> 2236285Sbrian#include <stdarg.h> 2336285Sbrian 2436285Sbrian#include <grp.h> 2536285Sbrian 2650479Speter#include "log.h" 2736285Sbrian#include "uidswap.h" 2836285Sbrian#include "xmalloc.h" 2936285Sbrian 3036285Sbrian/* 3136285Sbrian * Note: all these functions must work in all of the following cases: 3236285Sbrian * 1. euid=0, ruid=0 3336285Sbrian * 2. euid=0, ruid!=0 3436285Sbrian * 3. euid!=0, ruid!=0 3536285Sbrian * Additionally, they must work regardless of whether the system has 3636285Sbrian * POSIX saved uids or not. 3736285Sbrian */ 3836285Sbrian 3936285Sbrian#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 4036285Sbrian/* Lets assume that posix saved ids also work with seteuid, even though that 4136285Sbrian is not part of the posix specification. */ 4236285Sbrian#define SAVED_IDS_WORK_WITH_SETEUID 4336285Sbrian/* Saved effective uid. */ 4446686Sbrianstatic uid_t saved_euid = 0; 4536285Sbrianstatic gid_t saved_egid = 0; 4636285Sbrian#endif 4736285Sbrian 4836285Sbrian/* Saved effective uid. */ 4936285Sbrianstatic int privileged = 0; 5036285Sbrianstatic int temporarily_use_uid_effective = 0; 5136285Sbrianstatic gid_t *saved_egroups = NULL, *user_groups = NULL; 5236285Sbrianstatic int saved_egroupslen = -1, user_groupslen = -1; 5336285Sbrian 5436285Sbrian/* 5536285Sbrian * Temporarily changes to the given uid. If the effective user 5636285Sbrian * id is not root, this does nothing. This call cannot be nested. 5738557Sbrian */ 5838557Sbrianvoid 5938557Sbriantemporarily_use_uid(struct passwd *pw) 6036285Sbrian{ 6136285Sbrian /* Save the current euid, and egroups. */ 6236285Sbrian#ifdef SAVED_IDS_WORK_WITH_SETEUID 6336285Sbrian saved_euid = geteuid(); 6436285Sbrian saved_egid = getegid(); 6536285Sbrian debug("temporarily_use_uid: %u/%u (e=%u/%u)", 6636285Sbrian (u_int)pw->pw_uid, (u_int)pw->pw_gid, 6743313Sbrian (u_int)saved_euid, (u_int)saved_egid); 6843313Sbrian#ifndef HAVE_CYGWIN 6943313Sbrian if (saved_euid != 0) { 7036285Sbrian privileged = 0; 7136285Sbrian return; 7236285Sbrian } 7338174Sbrian#endif 7436285Sbrian#else 7536285Sbrian if (geteuid() != 0) { 7637386Sbrian privileged = 0; 7736285Sbrian return; 7836285Sbrian } 7936285Sbrian#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 8036285Sbrian 8137010Sbrian privileged = 1; 8236285Sbrian temporarily_use_uid_effective = 1; 8336285Sbrian 8436285Sbrian saved_egroupslen = getgroups(0, NULL); 8536285Sbrian if (saved_egroupslen < 0) 8636285Sbrian fatal("getgroups: %.100s", strerror(errno)); 8736285Sbrian if (saved_egroupslen > 0) { 8836285Sbrian saved_egroups = xrealloc(saved_egroups, 8936285Sbrian saved_egroupslen, sizeof(gid_t)); 9036285Sbrian if (getgroups(saved_egroupslen, saved_egroups) < 0) 9136285Sbrian fatal("getgroups: %.100s", strerror(errno)); 9236285Sbrian } else { /* saved_egroupslen == 0 */ 9336285Sbrian if (saved_egroups != NULL) 9436285Sbrian xfree(saved_egroups); 9536285Sbrian } 9636285Sbrian 9736285Sbrian /* set and save the user's groups */ 9836285Sbrian if (user_groupslen == -1) { 9936285Sbrian if (initgroups(pw->pw_name, pw->pw_gid) < 0) 10036285Sbrian fatal("initgroups: %s: %.100s", pw->pw_name, 10136285Sbrian strerror(errno)); 10236285Sbrian 10336285Sbrian user_groupslen = getgroups(0, NULL); 10436285Sbrian if (user_groupslen < 0) 10536285Sbrian fatal("getgroups: %.100s", strerror(errno)); 10636285Sbrian if (user_groupslen > 0) { 10736285Sbrian user_groups = xrealloc(user_groups, 10836285Sbrian user_groupslen, sizeof(gid_t)); 10936285Sbrian if (getgroups(user_groupslen, user_groups) < 0) 11036285Sbrian fatal("getgroups: %.100s", strerror(errno)); 11136285Sbrian } else { /* user_groupslen == 0 */ 11236285Sbrian if (user_groups) 11336285Sbrian xfree(user_groups); 11436285Sbrian } 11536285Sbrian } 11636285Sbrian /* Set the effective uid to the given (unprivileged) uid. */ 11736285Sbrian if (setgroups(user_groupslen, user_groups) < 0) 11836285Sbrian fatal("setgroups: %.100s", strerror(errno)); 11936285Sbrian#ifndef SAVED_IDS_WORK_WITH_SETEUID 12036285Sbrian /* Propagate the privileged gid to all of our gids. */ 12136285Sbrian if (setgid(getegid()) < 0) 12236285Sbrian debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 12336285Sbrian /* Propagate the privileged uid to all of our uids. */ 12436285Sbrian if (setuid(geteuid()) < 0) 12536285Sbrian debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 12636285Sbrian#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 12736285Sbrian if (setegid(pw->pw_gid) < 0) 12836285Sbrian fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 12936285Sbrian strerror(errno)); 13036285Sbrian if (seteuid(pw->pw_uid) == -1) 13136285Sbrian fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 13236285Sbrian strerror(errno)); 13336285Sbrian} 13436285Sbrian 13536285Sbrianvoid 13636285Sbrianpermanently_drop_suid(uid_t uid) 13736285Sbrian{ 13836285Sbrian uid_t old_uid = getuid(); 13936285Sbrian 14036285Sbrian debug("permanently_drop_suid: %u", (u_int)uid); 14136285Sbrian#if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 14236285Sbrian if (setresuid(uid, uid, uid) < 0) 14336285Sbrian fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 14436285Sbrian#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 14536285Sbrian if (setreuid(uid, uid) < 0) 14636285Sbrian fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno)); 14736285Sbrian#else 14836285Sbrian# ifndef SETEUID_BREAKS_SETUID 14936285Sbrian if (seteuid(uid) < 0) 15036285Sbrian fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno)); 15136285Sbrian# endif 15236285Sbrian if (setuid(uid) < 0) 15336285Sbrian fatal("setuid %u: %.100s", (u_int)uid, strerror(errno)); 15436285Sbrian#endif 15536285Sbrian 15636285Sbrian#ifndef HAVE_CYGWIN 15736285Sbrian /* Try restoration of UID if changed (test clearing of saved uid) */ 15836285Sbrian if (old_uid != uid && 15936285Sbrian (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 16036285Sbrian fatal("%s: was able to restore old [e]uid", __func__); 16136285Sbrian#endif 16236285Sbrian 16336285Sbrian /* Verify UID drop was successful */ 16437011Sbrian if (getuid() != uid || geteuid() != uid) { 16537011Sbrian fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 16637011Sbrian __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 16737011Sbrian } 16837011Sbrian} 16937011Sbrian 17036285Sbrian/* 17136285Sbrian * Restores to the original (privileged) uid. 17236285Sbrian */ 17336285Sbrianvoid 17436285Sbrianrestore_uid(void) 17536285Sbrian{ 17636285Sbrian /* it's a no-op unless privileged */ 17736285Sbrian if (!privileged) { 17836285Sbrian debug("restore_uid: (unprivileged)"); 17936285Sbrian return; 18036285Sbrian } 18136285Sbrian if (!temporarily_use_uid_effective) 18236285Sbrian fatal("restore_uid: temporarily_use_uid not effective"); 18336285Sbrian 18436285Sbrian#ifdef SAVED_IDS_WORK_WITH_SETEUID 18536285Sbrian debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 18636285Sbrian /* Set the effective uid back to the saved privileged uid. */ 18736285Sbrian if (seteuid(saved_euid) < 0) 18836285Sbrian fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 18936285Sbrian if (setegid(saved_egid) < 0) 19036285Sbrian fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 19136285Sbrian#else /* SAVED_IDS_WORK_WITH_SETEUID */ 19236314Sbrian /* 19337386Sbrian * We are unable to restore the real uid to its unprivileged value. 19437386Sbrian * Propagate the real uid (usually more privileged) to effective uid 19536285Sbrian * as well. 19636285Sbrian */ 19736285Sbrian setuid(getuid()); 19836285Sbrian setgid(getgid()); 19936285Sbrian#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 20036285Sbrian 20136285Sbrian if (setgroups(saved_egroupslen, saved_egroups) < 0) 20236285Sbrian fatal("setgroups: %.100s", strerror(errno)); 20336285Sbrian temporarily_use_uid_effective = 0; 20436285Sbrian} 20536285Sbrian 20636285Sbrian/* 20736285Sbrian * Permanently sets all uids to the given uid. This cannot be 20836285Sbrian * called while temporarily_use_uid is effective. 20936285Sbrian */ 21036285Sbrianvoid 21136285Sbrianpermanently_set_uid(struct passwd *pw) 21236285Sbrian{ 21336285Sbrian uid_t old_uid = getuid(); 21436285Sbrian gid_t old_gid = getgid(); 21536285Sbrian 21636285Sbrian if (pw == NULL) 21736285Sbrian fatal("permanently_set_uid: no user given"); 21836285Sbrian if (temporarily_use_uid_effective) 21936285Sbrian fatal("permanently_set_uid: temporarily_use_uid effective"); 22036285Sbrian debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 22136285Sbrian (u_int)pw->pw_gid); 22236285Sbrian 22336285Sbrian#if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) 22436285Sbrian if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 22536285Sbrian fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 22636285Sbrian#elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 22736285Sbrian if (setregid(pw->pw_gid, pw->pw_gid) < 0) 22836285Sbrian fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 22936285Sbrian#else 23037010Sbrian if (setegid(pw->pw_gid) < 0) 23136285Sbrian fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 23236285Sbrian if (setgid(pw->pw_gid) < 0) 23337010Sbrian fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 23436285Sbrian#endif 23536285Sbrian 23637019Sbrian#ifdef __APPLE__ 23736285Sbrian /* 23836285Sbrian * OS X requires initgroups after setgid to opt back into 23936285Sbrian * memberd support for >16 supplemental groups. 24036285Sbrian */ 24136285Sbrian if (initgroups(pw->pw_name, pw->pw_gid) < 0) 24236285Sbrian fatal("initgroups %.100s %u: %.100s", 24336285Sbrian pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 24436285Sbrian#endif 24536285Sbrian 24636285Sbrian#if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 24736285Sbrian if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 24836285Sbrian fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 24936285Sbrian#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 25036285Sbrian if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 25136285Sbrian fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 25236285Sbrian#else 25336285Sbrian# ifndef SETEUID_BREAKS_SETUID 25436285Sbrian if (seteuid(pw->pw_uid) < 0) 25536285Sbrian fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 25636285Sbrian# endif 25736285Sbrian if (setuid(pw->pw_uid) < 0) 25836285Sbrian fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 25937011Sbrian#endif 26037011Sbrian 26137011Sbrian#ifndef HAVE_CYGWIN 26237011Sbrian /* Try restoration of GID if changed (test clearing of saved gid) */ 26337011Sbrian if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 26437011Sbrian (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 26537011Sbrian fatal("%s: was able to restore old [e]gid", __func__); 26637011Sbrian#endif 26737011Sbrian 26837011Sbrian /* Verify GID drop was successful */ 26937011Sbrian if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 27037011Sbrian fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 27137011Sbrian __func__, (u_int)getgid(), (u_int)getegid(), 27237011Sbrian (u_int)pw->pw_gid); 27336285Sbrian } 27436285Sbrian 27536285Sbrian#ifndef HAVE_CYGWIN 27637019Sbrian /* Try restoration of UID if changed (test clearing of saved uid) */ 27736285Sbrian if (old_uid != pw->pw_uid && 27836285Sbrian (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 27936285Sbrian fatal("%s: was able to restore old [e]uid", __func__); 28036285Sbrian#endif 28137010Sbrian 28236285Sbrian /* Verify UID drop was successful */ 28336285Sbrian if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 28436285Sbrian fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 28536285Sbrian __func__, (u_int)getuid(), (u_int)geteuid(), 28636285Sbrian (u_int)pw->pw_uid); 28737141Sbrian } 28836285Sbrian} 28936285Sbrian