1 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 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 <sys/param.h> 18 #include <errno.h> 19 #include <pwd.h> 20 #include <string.h> 21 #include <unistd.h> 22 #include <stdarg.h> 23 24 #include <grp.h> 25 26 #include "log.h" 27 #include "uidswap.h" 28 #include "xmalloc.h" 29 30 /* 31 * Note: all these functions must work in all of the following cases: 32 * 1. euid=0, ruid=0 33 * 2. euid=0, ruid!=0 34 * 3. euid!=0, ruid!=0 35 * Additionally, they must work regardless of whether the system has 36 * POSIX saved uids or not. 37 */ 38 39 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 40 /* Lets assume that posix saved ids also work with seteuid, even though that 41 is not part of the posix specification. */ 42 #define SAVED_IDS_WORK_WITH_SETEUID 43 /* Saved effective uid. */ 44 static uid_t saved_euid = 0; 45 static gid_t saved_egid = 0; 46 #endif 47 48 /* Saved effective uid. */ 49 static int privileged = 0; 50 static int temporarily_use_uid_effective = 0; 51 static gid_t *saved_egroups = NULL, *user_groups = NULL; 52 static int saved_egroupslen = -1, user_groupslen = -1; 53 54 /* 55 * Temporarily changes to the given uid. If the effective user 56 * id is not root, this does nothing. This call cannot be nested. 57 */ 58 void 59 temporarily_use_uid(struct passwd *pw) 60 { 61 /* Save the current euid, and egroups. */ 62 #ifdef SAVED_IDS_WORK_WITH_SETEUID 63 saved_euid = geteuid(); 64 saved_egid = getegid(); 65 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 66 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 67 (u_int)saved_euid, (u_int)saved_egid); 68 #ifndef HAVE_CYGWIN 69 if (saved_euid != 0) { 70 privileged = 0; 71 return; 72 } 73 #endif 74 #else 75 if (geteuid() != 0) { 76 privileged = 0; 77 return; 78 } 79 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 80 81 privileged = 1; 82 temporarily_use_uid_effective = 1; 83 84 saved_egroupslen = getgroups(0, NULL); 85 if (saved_egroupslen < 0) 86 fatal("getgroups: %.100s", strerror(errno)); 87 if (saved_egroupslen > 0) { 88 saved_egroups = xrealloc(saved_egroups, 89 saved_egroupslen, sizeof(gid_t)); 90 if (getgroups(saved_egroupslen, saved_egroups) < 0) 91 fatal("getgroups: %.100s", strerror(errno)); 92 } else { /* saved_egroupslen == 0 */ 93 if (saved_egroups != NULL) 94 xfree(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 = xrealloc(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 if (user_groups) 113 xfree(user_groups); 114 } 115 } 116 /* Set the effective uid to the given (unprivileged) uid. */ 117 if (setgroups(user_groupslen, user_groups) < 0) 118 fatal("setgroups: %.100s", strerror(errno)); 119 #ifndef SAVED_IDS_WORK_WITH_SETEUID 120 /* Propagate the privileged gid to all of our gids. */ 121 if (setgid(getegid()) < 0) 122 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 123 /* Propagate the privileged uid to all of our uids. */ 124 if (setuid(geteuid()) < 0) 125 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 126 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 127 if (setegid(pw->pw_gid) < 0) 128 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 129 strerror(errno)); 130 if (seteuid(pw->pw_uid) == -1) 131 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 132 strerror(errno)); 133 } 134 135 void 136 permanently_drop_suid(uid_t uid) 137 { 138 uid_t old_uid = getuid(); 139 140 debug("permanently_drop_suid: %u", (u_int)uid); 141 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 142 if (setresuid(uid, uid, uid) < 0) 143 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 144 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 145 if (setreuid(uid, uid) < 0) 146 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno)); 147 #else 148 # ifndef SETEUID_BREAKS_SETUID 149 if (seteuid(uid) < 0) 150 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno)); 151 # endif 152 if (setuid(uid) < 0) 153 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno)); 154 #endif 155 156 #ifndef HAVE_CYGWIN 157 /* Try restoration of UID if changed (test clearing of saved uid) */ 158 if (old_uid != uid && 159 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 160 fatal("%s: was able to restore old [e]uid", __func__); 161 #endif 162 163 /* Verify UID drop was successful */ 164 if (getuid() != uid || geteuid() != uid) { 165 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 166 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 167 } 168 } 169 170 /* 171 * Restores to the original (privileged) uid. 172 */ 173 void 174 restore_uid(void) 175 { 176 /* it's a no-op unless privileged */ 177 if (!privileged) { 178 debug("restore_uid: (unprivileged)"); 179 return; 180 } 181 if (!temporarily_use_uid_effective) 182 fatal("restore_uid: temporarily_use_uid not effective"); 183 184 #ifdef SAVED_IDS_WORK_WITH_SETEUID 185 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 186 /* Set the effective uid back to the saved privileged uid. */ 187 if (seteuid(saved_euid) < 0) 188 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 189 if (setegid(saved_egid) < 0) 190 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 191 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 192 /* 193 * We are unable to restore the real uid to its unprivileged value. 194 * Propagate the real uid (usually more privileged) to effective uid 195 * as well. 196 */ 197 setuid(getuid()); 198 setgid(getgid()); 199 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 200 201 if (setgroups(saved_egroupslen, saved_egroups) < 0) 202 fatal("setgroups: %.100s", strerror(errno)); 203 temporarily_use_uid_effective = 0; 204 } 205 206 /* 207 * Permanently sets all uids to the given uid. This cannot be 208 * called while temporarily_use_uid is effective. 209 */ 210 void 211 permanently_set_uid(struct passwd *pw) 212 { 213 uid_t old_uid = getuid(); 214 gid_t old_gid = getgid(); 215 216 if (pw == NULL) 217 fatal("permanently_set_uid: no user given"); 218 if (temporarily_use_uid_effective) 219 fatal("permanently_set_uid: temporarily_use_uid effective"); 220 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 221 (u_int)pw->pw_gid); 222 223 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) 224 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 225 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 226 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 227 if (setregid(pw->pw_gid, pw->pw_gid) < 0) 228 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 229 #else 230 if (setegid(pw->pw_gid) < 0) 231 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 232 if (setgid(pw->pw_gid) < 0) 233 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 234 #endif 235 236 #ifdef __APPLE__ 237 /* 238 * OS X requires initgroups after setgid to opt back into 239 * memberd support for >16 supplemental groups. 240 */ 241 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 242 fatal("initgroups %.100s %u: %.100s", 243 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 244 #endif 245 246 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 247 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 248 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 249 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 250 if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 251 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 252 #else 253 # ifndef SETEUID_BREAKS_SETUID 254 if (seteuid(pw->pw_uid) < 0) 255 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 256 # endif 257 if (setuid(pw->pw_uid) < 0) 258 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 259 #endif 260 261 #ifndef HAVE_CYGWIN 262 /* Try restoration of GID if changed (test clearing of saved gid) */ 263 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 264 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 265 fatal("%s: was able to restore old [e]gid", __func__); 266 #endif 267 268 /* Verify GID drop was successful */ 269 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 270 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 271 __func__, (u_int)getgid(), (u_int)getegid(), 272 (u_int)pw->pw_gid); 273 } 274 275 #ifndef HAVE_CYGWIN 276 /* Try restoration of UID if changed (test clearing of saved uid) */ 277 if (old_uid != pw->pw_uid && 278 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 279 fatal("%s: was able to restore old [e]uid", __func__); 280 #endif 281 282 /* Verify UID drop was successful */ 283 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 284 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 285 __func__, (u_int)getuid(), (u_int)geteuid(), 286 (u_int)pw->pw_uid); 287 } 288 } 289