1/* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 deraadt Exp $ */ 2/* 3 * Author: Tatu Ylonen <ylo@cs.hut.fi> 4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 5 * All rights reserved 6 * Code for uid-swapping. 7 * 8 * As far as I am concerned, the code I have written for this software 9 * can be used freely for any purpose. Any derived versions of this 10 * software must be clearly marked as such, and if the derived work is 11 * incompatible with the protocol description in the RFC file, it must be 12 * called by a name other than "ssh" or "Secure Shell". 13 */ 14 15#include "includes.h" 16 17#include <errno.h> 18#include <pwd.h> 19#include <string.h> 20#include <unistd.h> 21#include <limits.h> 22#include <stdarg.h> 23#include <stdlib.h> 24 25#include <grp.h> 26 27#include "log.h" 28#include "uidswap.h" 29#include "xmalloc.h" 30 31/* 32 * Note: all these functions must work in all of the following cases: 33 * 1. euid=0, ruid=0 34 * 2. euid=0, ruid!=0 35 * 3. euid!=0, ruid!=0 36 * Additionally, they must work regardless of whether the system has 37 * POSIX saved uids or not. 38 */ 39 40#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 41/* Lets assume that posix saved ids also work with seteuid, even though that 42 is not part of the posix specification. */ 43#define SAVED_IDS_WORK_WITH_SETEUID 44/* Saved effective uid. */ 45static uid_t saved_euid = 0; 46static gid_t saved_egid = 0; 47#endif 48 49/* Saved effective uid. */ 50static int privileged = 0; 51static int temporarily_use_uid_effective = 0; 52static uid_t user_groups_uid; 53static gid_t *saved_egroups = NULL, *user_groups = NULL; 54static int saved_egroupslen = -1, user_groupslen = -1; 55 56/* 57 * Temporarily changes to the given uid. If the effective user 58 * id is not root, this does nothing. This call cannot be nested. 59 */ 60void 61temporarily_use_uid(struct passwd *pw) 62{ 63 /* Save the current euid, and egroups. */ 64#ifdef SAVED_IDS_WORK_WITH_SETEUID 65 saved_euid = geteuid(); 66 saved_egid = getegid(); 67 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 68 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 69 (u_int)saved_euid, (u_int)saved_egid); 70#ifndef HAVE_CYGWIN 71 if (saved_euid != 0) { 72 privileged = 0; 73 return; 74 } 75#endif 76#else 77 if (geteuid() != 0) { 78 privileged = 0; 79 return; 80 } 81#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 82 83 privileged = 1; 84 temporarily_use_uid_effective = 1; 85 86 saved_egroupslen = getgroups(0, NULL); 87 if (saved_egroupslen == -1) 88 fatal("getgroups: %.100s", strerror(errno)); 89 if (saved_egroupslen > 0) { 90 saved_egroups = xreallocarray(saved_egroups, 91 saved_egroupslen, sizeof(gid_t)); 92 if (getgroups(saved_egroupslen, saved_egroups) == -1) 93 fatal("getgroups: %.100s", strerror(errno)); 94 } else { /* saved_egroupslen == 0 */ 95 free(saved_egroups); 96 saved_egroups = NULL; 97 } 98 99 /* set and save the user's groups */ 100 if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) { 101 if (initgroups(pw->pw_name, pw->pw_gid) == -1) 102 fatal("initgroups: %s: %.100s", pw->pw_name, 103 strerror(errno)); 104 105 user_groupslen = getgroups(0, NULL); 106 if (user_groupslen == -1) 107 fatal("getgroups: %.100s", strerror(errno)); 108 if (user_groupslen > 0) { 109 user_groups = xreallocarray(user_groups, 110 user_groupslen, sizeof(gid_t)); 111 if (getgroups(user_groupslen, user_groups) == -1) 112 fatal("getgroups: %.100s", strerror(errno)); 113 } else { /* user_groupslen == 0 */ 114 free(user_groups); 115 user_groups = NULL; 116 } 117 user_groups_uid = pw->pw_uid; 118 } 119 /* Set the effective uid to the given (unprivileged) uid. */ 120 if (setgroups(user_groupslen, user_groups) == -1) 121 fatal("setgroups: %.100s", strerror(errno)); 122#ifndef SAVED_IDS_WORK_WITH_SETEUID 123 /* Propagate the privileged gid to all of our gids. */ 124 if (setgid(getegid()) == -1) 125 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 126 /* Propagate the privileged uid to all of our uids. */ 127 if (setuid(geteuid()) == -1) 128 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 129#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 130 if (setegid(pw->pw_gid) == -1) 131 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 132 strerror(errno)); 133 if (seteuid(pw->pw_uid) == -1) 134 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 135 strerror(errno)); 136} 137 138/* 139 * Restores to the original (privileged) uid. 140 */ 141void 142restore_uid(void) 143{ 144 /* it's a no-op unless privileged */ 145 if (!privileged) { 146 debug("restore_uid: (unprivileged)"); 147 return; 148 } 149 if (!temporarily_use_uid_effective) 150 fatal("restore_uid: temporarily_use_uid not effective"); 151 152#ifdef SAVED_IDS_WORK_WITH_SETEUID 153 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 154 /* Set the effective uid back to the saved privileged uid. */ 155 if (seteuid(saved_euid) == -1) 156 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 157 if (setegid(saved_egid) == -1) 158 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 159#else /* SAVED_IDS_WORK_WITH_SETEUID */ 160 /* 161 * We are unable to restore the real uid to its unprivileged value. 162 * Propagate the real uid (usually more privileged) to effective uid 163 * as well. 164 */ 165 if (setuid(getuid()) == -1) 166 fatal("%s: setuid failed: %s", __func__, strerror(errno)); 167 if (setgid(getgid()) == -1) 168 fatal("%s: setgid failed: %s", __func__, strerror(errno)); 169#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 170 171 if (setgroups(saved_egroupslen, saved_egroups) == -1) 172 fatal("setgroups: %.100s", strerror(errno)); 173 temporarily_use_uid_effective = 0; 174} 175 176/* 177 * Permanently sets all uids to the given uid. This cannot be 178 * called while temporarily_use_uid is effective. 179 */ 180void 181permanently_set_uid(struct passwd *pw) 182{ 183#ifndef NO_UID_RESTORATION_TEST 184 uid_t old_uid = getuid(); 185 gid_t old_gid = getgid(); 186#endif 187 188 if (pw == NULL) 189 fatal("permanently_set_uid: no user given"); 190 if (temporarily_use_uid_effective) 191 fatal("permanently_set_uid: temporarily_use_uid effective"); 192 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 193 (u_int)pw->pw_gid); 194 195 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1) 196 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 197 198#ifdef __APPLE__ 199 /* 200 * OS X requires initgroups after setgid to opt back into 201 * memberd support for >16 supplemental groups. 202 */ 203 if (initgroups(pw->pw_name, pw->pw_gid) == -1) 204 fatal("initgroups %.100s %u: %.100s", 205 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 206#endif 207 208 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1) 209 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 210 211#ifndef NO_UID_RESTORATION_TEST 212 /* Try restoration of GID if changed (test clearing of saved gid) */ 213 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 214 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 215 fatal("%s: was able to restore old [e]gid", __func__); 216#endif 217 218 /* Verify GID drop was successful */ 219 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 220 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 221 __func__, (u_int)getgid(), (u_int)getegid(), 222 (u_int)pw->pw_gid); 223 } 224 225#ifndef NO_UID_RESTORATION_TEST 226 /* Try restoration of UID if changed (test clearing of saved uid) */ 227 if (old_uid != pw->pw_uid && 228 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 229 fatal("%s: was able to restore old [e]uid", __func__); 230#endif 231 232 /* Verify UID drop was successful */ 233 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 234 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 235 __func__, (u_int)getuid(), (u_int)geteuid(), 236 (u_int)pw->pw_uid); 237 } 238} 239