1 /* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker 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. */ 45 static uid_t saved_euid = 0; 46 static gid_t saved_egid = 0; 47 #endif 48 49 /* Saved effective uid. */ 50 static int privileged = 0; 51 static int temporarily_use_uid_effective = 0; 52 static gid_t *saved_egroups = NULL, *user_groups = NULL; 53 static int saved_egroupslen = -1, user_groupslen = -1; 54 55 /* 56 * Temporarily changes to the given uid. If the effective user 57 * id is not root, this does nothing. This call cannot be nested. 58 */ 59 void 60 temporarily_use_uid(struct passwd *pw) 61 { 62 /* Save the current euid, and egroups. */ 63 #ifdef SAVED_IDS_WORK_WITH_SETEUID 64 saved_euid = geteuid(); 65 saved_egid = getegid(); 66 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 67 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 68 (u_int)saved_euid, (u_int)saved_egid); 69 #ifndef HAVE_CYGWIN 70 if (saved_euid != 0) { 71 privileged = 0; 72 return; 73 } 74 #endif 75 #else 76 if (geteuid() != 0) { 77 privileged = 0; 78 return; 79 } 80 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 81 82 privileged = 1; 83 temporarily_use_uid_effective = 1; 84 85 saved_egroupslen = getgroups(0, NULL); 86 if (saved_egroupslen < 0) 87 fatal("getgroups: %.100s", strerror(errno)); 88 if (saved_egroupslen > 0) { 89 saved_egroups = xreallocarray(saved_egroups, 90 saved_egroupslen, sizeof(gid_t)); 91 if (getgroups(saved_egroupslen, saved_egroups) < 0) 92 fatal("getgroups: %.100s", strerror(errno)); 93 } else { /* saved_egroupslen == 0 */ 94 free(saved_egroups); 95 } 96 97 /* set and save the user's groups */ 98 if (user_groupslen == -1) { 99 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 100 fatal("initgroups: %s: %.100s", pw->pw_name, 101 strerror(errno)); 102 103 user_groupslen = getgroups(0, NULL); 104 if (user_groupslen < 0) 105 fatal("getgroups: %.100s", strerror(errno)); 106 if (user_groupslen > 0) { 107 user_groups = xreallocarray(user_groups, 108 user_groupslen, sizeof(gid_t)); 109 if (getgroups(user_groupslen, user_groups) < 0) 110 fatal("getgroups: %.100s", strerror(errno)); 111 } else { /* user_groupslen == 0 */ 112 free(user_groups); 113 } 114 } 115 /* Set the effective uid to the given (unprivileged) uid. */ 116 if (setgroups(user_groupslen, user_groups) < 0) 117 fatal("setgroups: %.100s", strerror(errno)); 118 #ifndef SAVED_IDS_WORK_WITH_SETEUID 119 /* Propagate the privileged gid to all of our gids. */ 120 if (setgid(getegid()) < 0) 121 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 122 /* Propagate the privileged uid to all of our uids. */ 123 if (setuid(geteuid()) < 0) 124 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 125 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 126 if (setegid(pw->pw_gid) < 0) 127 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 128 strerror(errno)); 129 if (seteuid(pw->pw_uid) == -1) 130 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 131 strerror(errno)); 132 } 133 134 void 135 permanently_drop_suid(uid_t uid) 136 { 137 #ifndef NO_UID_RESTORATION_TEST 138 uid_t old_uid = getuid(); 139 #endif 140 141 debug("permanently_drop_suid: %u", (u_int)uid); 142 if (setresuid(uid, uid, uid) < 0) 143 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 144 145 #ifndef NO_UID_RESTORATION_TEST 146 /* 147 * Try restoration of UID if changed (test clearing of saved uid). 148 * 149 * Note that we don't do this on Cygwin, or on Solaris-based platforms 150 * where fine-grained privileges are available (the user might be 151 * deliberately allowed the right to setuid back to root). 152 */ 153 if (old_uid != uid && 154 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 155 fatal("%s: was able to restore old [e]uid", __func__); 156 #endif 157 158 /* Verify UID drop was successful */ 159 if (getuid() != uid || geteuid() != uid) { 160 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 161 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 162 } 163 } 164 165 /* 166 * Restores to the original (privileged) uid. 167 */ 168 void 169 restore_uid(void) 170 { 171 /* it's a no-op unless privileged */ 172 if (!privileged) { 173 debug("restore_uid: (unprivileged)"); 174 return; 175 } 176 if (!temporarily_use_uid_effective) 177 fatal("restore_uid: temporarily_use_uid not effective"); 178 179 #ifdef SAVED_IDS_WORK_WITH_SETEUID 180 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 181 /* Set the effective uid back to the saved privileged uid. */ 182 if (seteuid(saved_euid) < 0) 183 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 184 if (setegid(saved_egid) < 0) 185 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 186 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 187 /* 188 * We are unable to restore the real uid to its unprivileged value. 189 * Propagate the real uid (usually more privileged) to effective uid 190 * as well. 191 */ 192 setuid(getuid()); 193 setgid(getgid()); 194 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 195 196 if (setgroups(saved_egroupslen, saved_egroups) < 0) 197 fatal("setgroups: %.100s", strerror(errno)); 198 temporarily_use_uid_effective = 0; 199 } 200 201 /* 202 * Permanently sets all uids to the given uid. This cannot be 203 * called while temporarily_use_uid is effective. 204 */ 205 void 206 permanently_set_uid(struct passwd *pw) 207 { 208 #ifndef NO_UID_RESTORATION_TEST 209 uid_t old_uid = getuid(); 210 gid_t old_gid = getgid(); 211 #endif 212 213 if (pw == NULL) 214 fatal("permanently_set_uid: no user given"); 215 if (temporarily_use_uid_effective) 216 fatal("permanently_set_uid: temporarily_use_uid effective"); 217 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 218 (u_int)pw->pw_gid); 219 220 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 221 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 222 223 #ifdef __APPLE__ 224 /* 225 * OS X requires initgroups after setgid to opt back into 226 * memberd support for >16 supplemental groups. 227 */ 228 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 229 fatal("initgroups %.100s %u: %.100s", 230 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 231 #endif 232 233 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 234 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 235 236 #ifndef NO_UID_RESTORATION_TEST 237 /* Try restoration of GID if changed (test clearing of saved gid) */ 238 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 239 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 240 fatal("%s: was able to restore old [e]gid", __func__); 241 #endif 242 243 /* Verify GID drop was successful */ 244 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 245 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 246 __func__, (u_int)getgid(), (u_int)getegid(), 247 (u_int)pw->pw_gid); 248 } 249 250 #ifndef NO_UID_RESTORATION_TEST 251 /* Try restoration of UID if changed (test clearing of saved uid) */ 252 if (old_uid != pw->pw_uid && 253 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 254 fatal("%s: was able to restore old [e]uid", __func__); 255 #endif 256 257 /* Verify UID drop was successful */ 258 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 259 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 260 __func__, (u_int)getuid(), (u_int)geteuid(), 261 (u_int)pw->pw_uid); 262 } 263 } 264