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 (setresuid(uid, uid, uid) < 0) 142 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 143 144 #ifndef HAVE_CYGWIN 145 /* Try restoration of UID if changed (test clearing of saved uid) */ 146 if (old_uid != uid && 147 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 148 fatal("%s: was able to restore old [e]uid", __func__); 149 #endif 150 151 /* Verify UID drop was successful */ 152 if (getuid() != uid || geteuid() != uid) { 153 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 154 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 155 } 156 } 157 158 /* 159 * Restores to the original (privileged) uid. 160 */ 161 void 162 restore_uid(void) 163 { 164 /* it's a no-op unless privileged */ 165 if (!privileged) { 166 debug("restore_uid: (unprivileged)"); 167 return; 168 } 169 if (!temporarily_use_uid_effective) 170 fatal("restore_uid: temporarily_use_uid not effective"); 171 172 #ifdef SAVED_IDS_WORK_WITH_SETEUID 173 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 174 /* Set the effective uid back to the saved privileged uid. */ 175 if (seteuid(saved_euid) < 0) 176 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 177 if (setegid(saved_egid) < 0) 178 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 179 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 180 /* 181 * We are unable to restore the real uid to its unprivileged value. 182 * Propagate the real uid (usually more privileged) to effective uid 183 * as well. 184 */ 185 setuid(getuid()); 186 setgid(getgid()); 187 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 188 189 if (setgroups(saved_egroupslen, saved_egroups) < 0) 190 fatal("setgroups: %.100s", strerror(errno)); 191 temporarily_use_uid_effective = 0; 192 } 193 194 /* 195 * Permanently sets all uids to the given uid. This cannot be 196 * called while temporarily_use_uid is effective. 197 */ 198 void 199 permanently_set_uid(struct passwd *pw) 200 { 201 uid_t old_uid = getuid(); 202 gid_t old_gid = getgid(); 203 204 if (pw == NULL) 205 fatal("permanently_set_uid: no user given"); 206 if (temporarily_use_uid_effective) 207 fatal("permanently_set_uid: temporarily_use_uid effective"); 208 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 209 (u_int)pw->pw_gid); 210 211 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 212 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 213 214 #ifdef __APPLE__ 215 /* 216 * OS X requires initgroups after setgid to opt back into 217 * memberd support for >16 supplemental groups. 218 */ 219 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 220 fatal("initgroups %.100s %u: %.100s", 221 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 222 #endif 223 224 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 225 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 226 227 #ifndef HAVE_CYGWIN 228 /* Try restoration of GID if changed (test clearing of saved gid) */ 229 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 230 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 231 fatal("%s: was able to restore old [e]gid", __func__); 232 #endif 233 234 /* Verify GID drop was successful */ 235 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 236 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 237 __func__, (u_int)getgid(), (u_int)getegid(), 238 (u_int)pw->pw_gid); 239 } 240 241 #ifndef HAVE_CYGWIN 242 /* Try restoration of UID if changed (test clearing of saved uid) */ 243 if (old_uid != pw->pw_uid && 244 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 245 fatal("%s: was able to restore old [e]uid", __func__); 246 #endif 247 248 /* Verify UID drop was successful */ 249 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 250 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 251 __func__, (u_int)getuid(), (u_int)geteuid(), 252 (u_int)pw->pw_uid); 253 } 254 } 255