1 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */ 2 /* 3 * Author: Tatu Ylonen <ylo (at) cs.hut.fi> 4 * Copyright (c) 1995 Tatu Ylonen <ylo (at) 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 #ifdef ANDROID 31 #include <private/android_filesystem_config.h> 32 #include <sys/capability.h> 33 #include <linux/prctl.h> 34 #endif 35 36 /* 37 * Note: all these functions must work in all of the following cases: 38 * 1. euid=0, ruid=0 39 * 2. euid=0, ruid!=0 40 * 3. euid!=0, ruid!=0 41 * Additionally, they must work regardless of whether the system has 42 * POSIX saved uids or not. 43 */ 44 45 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 46 /* Lets assume that posix saved ids also work with seteuid, even though that 47 is not part of the posix specification. */ 48 #define SAVED_IDS_WORK_WITH_SETEUID 49 /* Saved effective uid. */ 50 static uid_t saved_euid = 0; 51 static gid_t saved_egid = 0; 52 #endif 53 54 /* Saved effective uid. */ 55 static int privileged = 0; 56 static int temporarily_use_uid_effective = 0; 57 static gid_t *saved_egroups = NULL, *user_groups = NULL; 58 static int saved_egroupslen = -1, user_groupslen = -1; 59 60 /* 61 * Temporarily changes to the given uid. If the effective user 62 * id is not root, this does nothing. This call cannot be nested. 63 */ 64 void 65 temporarily_use_uid(struct passwd *pw) 66 { 67 /* Save the current euid, and egroups. */ 68 #ifdef SAVED_IDS_WORK_WITH_SETEUID 69 saved_euid = geteuid(); 70 saved_egid = getegid(); 71 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 72 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 73 (u_int)saved_euid, (u_int)saved_egid); 74 #ifndef HAVE_CYGWIN 75 if (saved_euid != 0) { 76 privileged = 0; 77 return; 78 } 79 #endif 80 #else 81 if (geteuid() != 0) { 82 privileged = 0; 83 return; 84 } 85 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 86 87 privileged = 1; 88 temporarily_use_uid_effective = 1; 89 90 saved_egroupslen = getgroups(0, NULL); 91 if (saved_egroupslen < 0) 92 fatal("getgroups: %.100s", strerror(errno)); 93 if (saved_egroupslen > 0) { 94 saved_egroups = xrealloc(saved_egroups, 95 saved_egroupslen, sizeof(gid_t)); 96 if (getgroups(saved_egroupslen, saved_egroups) < 0) 97 fatal("getgroups: %.100s", strerror(errno)); 98 } else { /* saved_egroupslen == 0 */ 99 if (saved_egroups != NULL) 100 xfree(saved_egroups); 101 } 102 103 /* set and save the user's groups */ 104 if (user_groupslen == -1) { 105 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 106 fatal("initgroups: %s: %.100s", pw->pw_name, 107 strerror(errno)); 108 109 user_groupslen = getgroups(0, NULL); 110 if (user_groupslen < 0) 111 fatal("getgroups: %.100s", strerror(errno)); 112 if (user_groupslen > 0) { 113 user_groups = xrealloc(user_groups, 114 user_groupslen, sizeof(gid_t)); 115 if (getgroups(user_groupslen, user_groups) < 0) 116 fatal("getgroups: %.100s", strerror(errno)); 117 } else { /* user_groupslen == 0 */ 118 if (user_groups) 119 xfree(user_groups); 120 } 121 } 122 /* Set the effective uid to the given (unprivileged) uid. */ 123 if (setgroups(user_groupslen, user_groups) < 0) 124 fatal("setgroups: %.100s", strerror(errno)); 125 #ifndef SAVED_IDS_WORK_WITH_SETEUID 126 /* Propagate the privileged gid to all of our gids. */ 127 if (setgid(getegid()) < 0) 128 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 129 /* Propagate the privileged uid to all of our uids. */ 130 if (setuid(geteuid()) < 0) 131 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 132 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 133 if (setegid(pw->pw_gid) < 0) 134 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 135 strerror(errno)); 136 if (seteuid(pw->pw_uid) == -1) 137 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 138 strerror(errno)); 139 } 140 141 void 142 permanently_drop_suid(uid_t uid) 143 { 144 uid_t old_uid = getuid(); 145 146 debug("permanently_drop_suid: %u", (u_int)uid); 147 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 148 if (setresuid(uid, uid, uid) < 0) 149 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 150 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 151 if (setreuid(uid, uid) < 0) 152 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno)); 153 #else 154 # ifndef SETEUID_BREAKS_SETUID 155 if (seteuid(uid) < 0) 156 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno)); 157 # endif 158 if (setuid(uid) < 0) 159 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno)); 160 #endif 161 162 #ifndef HAVE_CYGWIN 163 /* Try restoration of UID if changed (test clearing of saved uid) */ 164 if (old_uid != uid && 165 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 166 fatal("%s: was able to restore old [e]uid", __func__); 167 #endif 168 169 /* Verify UID drop was successful */ 170 if (getuid() != uid || geteuid() != uid) { 171 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 172 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 173 } 174 } 175 176 /* 177 * Restores to the original (privileged) uid. 178 */ 179 void 180 restore_uid(void) 181 { 182 /* it's a no-op unless privileged */ 183 if (!privileged) { 184 debug("restore_uid: (unprivileged)"); 185 return; 186 } 187 if (!temporarily_use_uid_effective) 188 fatal("restore_uid: temporarily_use_uid not effective"); 189 190 #ifdef SAVED_IDS_WORK_WITH_SETEUID 191 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 192 /* Set the effective uid back to the saved privileged uid. */ 193 if (seteuid(saved_euid) < 0) 194 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 195 if (setegid(saved_egid) < 0) 196 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 197 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 198 /* 199 * We are unable to restore the real uid to its unprivileged value. 200 * Propagate the real uid (usually more privileged) to effective uid 201 * as well. 202 */ 203 setuid(getuid()); 204 setgid(getgid()); 205 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 206 207 if (setgroups(saved_egroupslen, saved_egroups) < 0) 208 fatal("setgroups: %.100s", strerror(errno)); 209 temporarily_use_uid_effective = 0; 210 } 211 212 /* 213 * Permanently sets all uids to the given uid. This cannot be 214 * called while temporarily_use_uid is effective. 215 */ 216 void 217 permanently_set_uid(struct passwd *pw) 218 { 219 uid_t old_uid = getuid(); 220 gid_t old_gid = getgid(); 221 #ifdef ANDROID 222 struct __user_cap_header_struct header; 223 struct __user_cap_data_struct cap; 224 #endif 225 226 if (pw == NULL) 227 fatal("permanently_set_uid: no user given"); 228 if (temporarily_use_uid_effective) 229 fatal("permanently_set_uid: temporarily_use_uid effective"); 230 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 231 (u_int)pw->pw_gid); 232 233 #ifdef ANDROID 234 if (pw->pw_uid == AID_SHELL) { 235 prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0); 236 237 /* add extra groups needed for shell user: 238 ** AID_LOG to read system logs (adb logcat) 239 ** AID_INPUT to diagnose input issues (getevent) 240 ** AID_INET to diagnose network issues (netcfg, ping) 241 ** AID_GRAPHICS to access the frame buffer 242 ** AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump) 243 ** AID_SDCARD_RW to allow writing to the SD card 244 ** AID_MOUNT to allow unmounting the SD card before rebooting 245 ** AID_NET_BW_STATS to read out qtaguid statistics 246 */ 247 gid_t groups[] = { AID_LOG, AID_INPUT, AID_INET, AID_GRAPHICS, 248 AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_RW, 249 AID_MOUNT, AID_NET_BW_STATS }; 250 setgroups(sizeof(groups)/sizeof(groups[0]), groups); 251 } 252 #endif 253 254 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) 255 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 256 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 257 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 258 if (setregid(pw->pw_gid, pw->pw_gid) < 0) 259 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 260 #else 261 if (setegid(pw->pw_gid) < 0) 262 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 263 if (setgid(pw->pw_gid) < 0) 264 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 265 #endif 266 267 #ifdef __APPLE__ 268 /* 269 * OS X requires initgroups after setgid to opt back into 270 * memberd support for >16 supplemental groups. 271 */ 272 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 273 fatal("initgroups %.100s %u: %.100s", 274 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 275 #endif 276 277 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 278 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 279 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 280 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 281 if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 282 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 283 #else 284 # ifndef SETEUID_BREAKS_SETUID 285 if (seteuid(pw->pw_uid) < 0) 286 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 287 # endif 288 if (setuid(pw->pw_uid) < 0) 289 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 290 #endif 291 292 #ifndef HAVE_CYGWIN 293 /* Try restoration of GID if changed (test clearing of saved gid) */ 294 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 295 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 296 fatal("%s: was able to restore old [e]gid", __func__); 297 #endif 298 299 /* Verify GID drop was successful */ 300 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 301 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 302 __func__, (u_int)getgid(), (u_int)getegid(), 303 (u_int)pw->pw_gid); 304 } 305 306 #ifndef HAVE_CYGWIN 307 /* Try restoration of UID if changed (test clearing of saved uid) */ 308 if (old_uid != pw->pw_uid && 309 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 310 fatal("%s: was able to restore old [e]uid", __func__); 311 #endif 312 313 /* Verify UID drop was successful */ 314 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 315 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 316 __func__, (u_int)getuid(), (u_int)geteuid(), 317 (u_int)pw->pw_uid); 318 } 319 320 #ifdef ANDROID 321 if (pw->pw_uid == AID_SHELL) { 322 /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */ 323 header.version = _LINUX_CAPABILITY_VERSION; 324 header.pid = 0; 325 cap.effective = cap.permitted = (1 << CAP_SYS_BOOT); 326 cap.inheritable = 0; 327 capset(&header, &cap); 328 } 329 #endif 330 331 } 332
