1 /* 2 * Author: Tatu Ylonen <ylo@cs.hut.fi> 3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 4 * All rights reserved 5 * Code for uid-swapping. 6 * 7 * As far as I am concerned, the code I have written for this software 8 * can be used freely for any purpose. Any derived versions of this 9 * software must be clearly marked as such, and if the derived work is 10 * incompatible with the protocol description in the RFC file, it must be 11 * called by a name other than "ssh" or "Secure Shell". 12 */ 13 14 #include "includes.h" 15 RCSID("$OpenBSD: uidswap.c,v 1.24 2003/05/29 16:58:45 deraadt Exp $"); 16 17 #include "log.h" 18 #include "uidswap.h" 19 #include "xmalloc.h" 20 21 /* 22 * Note: all these functions must work in all of the following cases: 23 * 1. euid=0, ruid=0 24 * 2. euid=0, ruid!=0 25 * 3. euid!=0, ruid!=0 26 * Additionally, they must work regardless of whether the system has 27 * POSIX saved uids or not. 28 */ 29 30 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 31 /* Lets assume that posix saved ids also work with seteuid, even though that 32 is not part of the posix specification. */ 33 #define SAVED_IDS_WORK_WITH_SETEUID 34 /* Saved effective uid. */ 35 static uid_t saved_euid = 0; 36 static gid_t saved_egid = 0; 37 #endif 38 39 /* Saved effective uid. */ 40 static int privileged = 0; 41 static int temporarily_use_uid_effective = 0; 42 static gid_t *saved_egroups = NULL, *user_groups = NULL; 43 static int saved_egroupslen = -1, user_groupslen = -1; 44 45 /* 46 * Temporarily changes to the given uid. If the effective user 47 * id is not root, this does nothing. This call cannot be nested. 48 */ 49 void 50 temporarily_use_uid(struct passwd *pw) 51 { 52 /* Save the current euid, and egroups. */ 53 #ifdef SAVED_IDS_WORK_WITH_SETEUID 54 saved_euid = geteuid(); 55 saved_egid = getegid(); 56 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 57 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 58 (u_int)saved_euid, (u_int)saved_egid); 59 if (saved_euid != 0) { 60 privileged = 0; 61 return; 62 } 63 #else 64 if (geteuid() != 0) { 65 privileged = 0; 66 return; 67 } 68 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 69 70 privileged = 1; 71 temporarily_use_uid_effective = 1; 72 73 saved_egroupslen = getgroups(0, NULL); 74 if (saved_egroupslen < 0) 75 fatal("getgroups: %.100s", strerror(errno)); 76 if (saved_egroupslen > 0) { 77 saved_egroups = xrealloc(saved_egroups, 78 saved_egroupslen * sizeof(gid_t)); 79 if (getgroups(saved_egroupslen, saved_egroups) < 0) 80 fatal("getgroups: %.100s", strerror(errno)); 81 } else { /* saved_egroupslen == 0 */ 82 if (saved_egroups != NULL) 83 xfree(saved_egroups); 84 } 85 86 /* set and save the user's groups */ 87 if (user_groupslen == -1) { 88 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 89 fatal("initgroups: %s: %.100s", pw->pw_name, 90 strerror(errno)); 91 92 user_groupslen = getgroups(0, NULL); 93 if (user_groupslen < 0) 94 fatal("getgroups: %.100s", strerror(errno)); 95 if (user_groupslen > 0) { 96 user_groups = xrealloc(user_groups, 97 user_groupslen * sizeof(gid_t)); 98 if (getgroups(user_groupslen, user_groups) < 0) 99 fatal("getgroups: %.100s", strerror(errno)); 100 } else { /* user_groupslen == 0 */ 101 if (user_groups) 102 xfree(user_groups); 103 } 104 } 105 /* Set the effective uid to the given (unprivileged) uid. */ 106 if (setgroups(user_groupslen, user_groups) < 0) 107 fatal("setgroups: %.100s", strerror(errno)); 108 #ifndef SAVED_IDS_WORK_WITH_SETEUID 109 /* Propagate the privileged gid to all of our gids. */ 110 if (setgid(getegid()) < 0) 111 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 112 /* Propagate the privileged uid to all of our uids. */ 113 if (setuid(geteuid()) < 0) 114 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 115 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 116 if (setegid(pw->pw_gid) < 0) 117 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 118 strerror(errno)); 119 if (seteuid(pw->pw_uid) == -1) 120 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 121 strerror(errno)); 122 } 123 124 /* 125 * Restores to the original (privileged) uid. 126 */ 127 void 128 restore_uid(void) 129 { 130 /* it's a no-op unless privileged */ 131 if (!privileged) { 132 debug("restore_uid: (unprivileged)"); 133 return; 134 } 135 if (!temporarily_use_uid_effective) 136 fatal("restore_uid: temporarily_use_uid not effective"); 137 138 #ifdef SAVED_IDS_WORK_WITH_SETEUID 139 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 140 /* Set the effective uid back to the saved privileged uid. */ 141 if (seteuid(saved_euid) < 0) 142 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 143 if (setegid(saved_egid) < 0) 144 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 145 #else /* SAVED_IDS_WORK_WITH_SETEUID */ 146 /* 147 * We are unable to restore the real uid to its unprivileged value. 148 * Propagate the real uid (usually more privileged) to effective uid 149 * as well. 150 */ 151 setuid(getuid()); 152 setgid(getgid()); 153 #endif /* SAVED_IDS_WORK_WITH_SETEUID */ 154 155 if (setgroups(saved_egroupslen, saved_egroups) < 0) 156 fatal("setgroups: %.100s", strerror(errno)); 157 temporarily_use_uid_effective = 0; 158 } 159 160 /* 161 * Permanently sets all uids to the given uid. This cannot be 162 * called while temporarily_use_uid is effective. 163 */ 164 void 165 permanently_set_uid(struct passwd *pw) 166 { 167 uid_t old_uid = getuid(); 168 gid_t old_gid = getgid(); 169 170 if (temporarily_use_uid_effective) 171 fatal("permanently_set_uid: temporarily_use_uid effective"); 172 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 173 (u_int)pw->pw_gid); 174 175 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) 176 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 177 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 178 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 179 if (setregid(pw->pw_gid, pw->pw_gid) < 0) 180 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 181 #else 182 if (setegid(pw->pw_gid) < 0) 183 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 184 if (setgid(pw->pw_gid) < 0) 185 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 186 #endif 187 188 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 189 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 190 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 191 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 192 if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 193 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 194 #else 195 # ifndef SETEUID_BREAKS_SETUID 196 if (seteuid(pw->pw_uid) < 0) 197 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 198 # endif 199 if (setuid(pw->pw_uid) < 0) 200 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 201 #endif 202 203 /* Try restoration of GID if changed (test clearing of saved gid) */ 204 if (old_gid != pw->pw_gid && 205 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 206 fatal("%s: was able to restore old [e]gid", __func__); 207 208 /* Verify GID drop was successful */ 209 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 210 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 211 __func__, (u_int)getgid(), (u_int)getegid(), 212 (u_int)pw->pw_gid); 213 } 214 215 #ifndef HAVE_CYGWIN 216 /* Try restoration of UID if changed (test clearing of saved uid) */ 217 if (old_uid != pw->pw_uid && 218 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 219 fatal("%s: was able to restore old [e]uid", __func__); 220 #endif 221 222 /* Verify UID drop was successful */ 223 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 224 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 225 __func__, (u_int)getuid(), (u_int)geteuid(), 226 (u_int)pw->pw_uid); 227 } 228 } 229