1 /* $OpenBSD: uidswap.c,v 1.37 2015/01/16 06:40:12 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 <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 #ifdef ANDROID 32 #include <private/android_filesystem_config.h> 33 #include <sys/capability.h> 34 #include <sys/prctl.h> 35 #endif 36 37 /* 38 * Note: all these functions must work in all of the following cases: 39 * 1. euid=0, ruid=0 40 * 2. euid=0, ruid!=0 41 * 3. euid!=0, ruid!=0 42 * Additionally, they must work regardless of whether the system has 43 * POSIX saved uids or not. 44 */ 45 46 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 47 /* Lets assume that posix saved ids also work with seteuid, even though that 48 is not part of the posix specification. */ 49 #define SAVED_IDS_WORK_WITH_SETEUID 50 /* Saved effective uid. */ 51 static uid_t saved_euid = 0; 52 static gid_t saved_egid = 0; 53 #endif 54 55 /* Saved effective uid. */ 56 static int privileged = 0; 57 static int temporarily_use_uid_effective = 0; 58 static gid_t *saved_egroups = NULL, *user_groups = NULL; 59 static int saved_egroupslen = -1, user_groupslen = -1; 60 61 /* 62 * Temporarily changes to the given uid. If the effective user 63 * id is not root, this does nothing. This call cannot be nested. 64 */ 65 void 66 temporarily_use_uid(struct passwd *pw) 67 { 68 /* Save the current euid, and egroups. */ 69 #ifdef SAVED_IDS_WORK_WITH_SETEUID 70 saved_euid = geteuid(); 71 saved_egid = getegid(); 72 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 73 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 74 (u_int)saved_euid, (u_int)saved_egid); 75 #ifndef HAVE_CYGWIN 76 if (saved_euid != 0) { 77 privileged = 0; 78 return; 79 } 80 #endif 81 #else 82 if (geteuid() != 0) { 83 privileged = 0; 84 return; 85 } 86 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 87 88 privileged = 1; 89 temporarily_use_uid_effective = 1; 90 91 saved_egroupslen = getgroups(0, NULL); 92 if (saved_egroupslen < 0) 93 fatal("getgroups: %.100s", strerror(errno)); 94 if (saved_egroupslen > 0) { 95 saved_egroups = xrealloc(saved_egroups, 96 saved_egroupslen, sizeof(gid_t)); 97 if (getgroups(saved_egroupslen, saved_egroups) < 0) 98 fatal("getgroups: %.100s", strerror(errno)); 99 } else { /* saved_egroupslen == 0 */ 100 free(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 free(user_groups); 119 } 120 } 121 /* Set the effective uid to the given (unprivileged) uid. */ 122 if (setgroups(user_groupslen, user_groups) < 0) 123 fatal("setgroups: %.100s", strerror(errno)); 124 #ifndef SAVED_IDS_WORK_WITH_SETEUID 125 /* Propagate the privileged gid to all of our gids. */ 126 if (setgid(getegid()) < 0) 127 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 128 /* Propagate the privileged uid to all of our uids. */ 129 if (setuid(geteuid()) < 0) 130 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 131 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 132 if (setegid(pw->pw_gid) < 0) 133 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 134 strerror(errno)); 135 if (seteuid(pw->pw_uid) == -1) 136 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 137 strerror(errno)); 138 } 139 140 void 141 permanently_drop_suid(uid_t uid) 142 { 143 #ifndef HAVE_CYGWIN 144 uid_t old_uid = getuid(); 145 #endif 146 147 debug("permanently_drop_suid: %u", (u_int)uid); 148 if (setresuid(uid, uid, uid) < 0) 149 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 150 151 #ifndef HAVE_CYGWIN 152 /* Try restoration of UID if changed (test clearing of saved uid) */ 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 HAVE_CYGWIN 209 uid_t old_uid = getuid(); 210 gid_t old_gid = getgid(); 211 #endif 212 #if defined(ANDROID) 213 struct __user_cap_header_struct header; 214 struct __user_cap_data_struct cap; 215 #endif 216 217 if (pw == NULL) 218 fatal("permanently_set_uid: no user given"); 219 if (temporarily_use_uid_effective) 220 fatal("permanently_set_uid: temporarily_use_uid effective"); 221 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 222 (u_int)pw->pw_gid); 223 224 #if defined(ANDROID) 225 if (pw->pw_uid == AID_SHELL) { 226 prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0); 227 228 /* add extra groups needed for shell user: 229 * - AID_LOG to read system logs (adb logcat) 230 * - AID_INPUT to diagnose input issues (getevent) 231 * - AID_INET to diagnose network issues (netcfg, ping) 232 * - AID_GRAPHICS to access the frame buffer 233 * - AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump) 234 * - AID_SDCARD_RW to allow writing to the SD card 235 * - AID_MOUNT to allow unmounting the SD card before rebooting 236 * - AID_NET_BW_STATS to read out qtaguid statistics. */ 237 gid_t groups[] = {AID_LOG, AID_INPUT, AID_INET, 238 AID_GRAPHICS, AID_NET_BT, AID_NET_BT_ADMIN, 239 AID_SDCARD_RW, AID_MOUNT, AID_NET_BW_STATS}; 240 setgroups(sizeof(groups)/sizeof(groups[0]), groups); 241 } 242 #endif 243 244 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 245 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 246 247 #ifdef __APPLE__ 248 /* 249 * OS X requires initgroups after setgid to opt back into 250 * memberd support for >16 supplemental groups. 251 */ 252 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 253 fatal("initgroups %.100s %u: %.100s", 254 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 255 #endif 256 257 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 258 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 259 260 #ifndef HAVE_CYGWIN 261 /* Try restoration of GID if changed (test clearing of saved gid) */ 262 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 263 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 264 fatal("%s: was able to restore old [e]gid", __func__); 265 #endif 266 267 /* Verify GID drop was successful */ 268 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 269 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 270 __func__, (u_int)getgid(), (u_int)getegid(), 271 (u_int)pw->pw_gid); 272 } 273 274 #ifndef HAVE_CYGWIN 275 /* Try restoration of UID if changed (test clearing of saved uid) */ 276 if (old_uid != pw->pw_uid && 277 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 278 fatal("%s: was able to restore old [e]uid", __func__); 279 #endif 280 281 /* Verify UID drop was successful */ 282 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 283 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 284 __func__, (u_int)getuid(), (u_int)geteuid(), 285 (u_int)pw->pw_uid); 286 } 287 288 #ifdef ANDROID 289 if (pw->pw_uid == AID_SHELL) { 290 /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */ 291 header.version = _LINUX_CAPABILITY_VERSION; 292 header.pid = 0; 293 cap.effective = cap.permitted = (1 << CAP_SYS_BOOT); 294 cap.inheritable = 0; 295 capset(&header, &cap); 296 } 297 #endif 298 299 } 300
