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. */ 44static uid_t saved_euid = 0; 45static gid_t saved_egid = 0; 46#endif 47 48/* Saved effective uid. */ 49static int privileged = 0; 50static int temporarily_use_uid_effective = 0; 51static gid_t *saved_egroups = NULL, *user_groups = NULL; 52static 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 */ 58void 59temporarily_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#if __APPLE__ 97 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 98 fatal("initgroups: %s: %.100s", pw->pw_name, 99 strerror(errno)); 100#else 101 /* set and save the user's groups */ 102 if (user_groupslen == -1) { 103 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 104 fatal("initgroups: %s: %.100s", pw->pw_name, 105 strerror(errno)); 106 107 user_groupslen = getgroups(0, NULL); 108 if (user_groupslen < 0) 109 fatal("getgroups: %.100s", strerror(errno)); 110 if (user_groupslen > 0) { 111 user_groups = xrealloc(user_groups, 112 user_groupslen, sizeof(gid_t)); 113 if (getgroups(user_groupslen, user_groups) < 0) 114 fatal("getgroups: %.100s", strerror(errno)); 115 } else { /* user_groupslen == 0 */ 116 if (user_groups) 117 xfree(user_groups); 118 } 119 } 120 /* Set the effective uid to the given (unprivileged) uid. */ 121 if (setgroups(user_groupslen, user_groups) < 0) 122 fatal("setgroups: %.100s", strerror(errno)); 123#endif 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 140void 141permanently_drop_suid(uid_t uid) 142{ 143 uid_t old_uid = getuid(); 144 145 debug("permanently_drop_suid: %u", (u_int)uid); 146 if (setresuid(uid, uid, uid) < 0) 147 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 148 149#ifndef HAVE_CYGWIN 150 /* Try restoration of UID if changed (test clearing of saved uid) */ 151 if (old_uid != uid && 152 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 153 fatal("%s: was able to restore old [e]uid", __func__); 154#endif 155 156 /* Verify UID drop was successful */ 157 if (getuid() != uid || geteuid() != uid) { 158 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 159 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 160 } 161} 162 163/* 164 * Restores to the original (privileged) uid. 165 */ 166void 167restore_uid(void) 168{ 169 /* it's a no-op unless privileged */ 170 if (!privileged) { 171 debug("restore_uid: (unprivileged)"); 172 return; 173 } 174 if (!temporarily_use_uid_effective) 175 fatal("restore_uid: temporarily_use_uid not effective"); 176 177#ifdef SAVED_IDS_WORK_WITH_SETEUID 178 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 179 /* Set the effective uid back to the saved privileged uid. */ 180 if (seteuid(saved_euid) < 0) 181 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 182 if (setegid(saved_egid) < 0) 183 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 184#else /* SAVED_IDS_WORK_WITH_SETEUID */ 185 /* 186 * We are unable to restore the real uid to its unprivileged value. 187 * Propagate the real uid (usually more privileged) to effective uid 188 * as well. 189 */ 190 setuid(getuid()); 191 setgid(getgid()); 192#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 193 194 if (setgroups(saved_egroupslen, saved_egroups) < 0) 195 fatal("setgroups: %.100s", strerror(errno)); 196 temporarily_use_uid_effective = 0; 197} 198 199/* 200 * Permanently sets all uids to the given uid. This cannot be 201 * called while temporarily_use_uid is effective. 202 */ 203void 204permanently_set_uid(struct passwd *pw) 205{ 206 uid_t old_uid = getuid(); 207 gid_t old_gid = getgid(); 208 209 if (pw == NULL) 210 fatal("permanently_set_uid: no user given"); 211 if (temporarily_use_uid_effective) 212 fatal("permanently_set_uid: temporarily_use_uid effective"); 213 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 214 (u_int)pw->pw_gid); 215 216 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 217 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 218 219#ifdef __APPLE__ 220 /* 221 * OS X requires initgroups after setgid to opt back into 222 * memberd support for >16 supplemental groups. 223 * 224 * initgroups is not needed for the network child because it has 225 * reached a steady-state and will not need to allocate any new 226 * resources. Allows for a cleaner sandbox profile. 227 * 228 * initgroups is needed for all other children so that anything spawned 229 * or used by this child (i.e. the user shell) will opt into membership 230 * services. 231 */ 232 if ( 0 != strcmp(pw->pw_name, SSH_PRIVSEP_USER) && 233 initgroups(pw->pw_name, pw->pw_gid) < 0) 234 fatal("initgroups %.100s %u: %.100s", 235 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 236#endif 237 238 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 239 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 240 241#ifndef HAVE_CYGWIN 242 /* Try restoration of GID if changed (test clearing of saved gid) */ 243 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 244 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 245 fatal("%s: was able to restore old [e]gid", __func__); 246#endif 247 248 /* Verify GID drop was successful */ 249 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 250 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 251 __func__, (u_int)getgid(), (u_int)getegid(), 252 (u_int)pw->pw_gid); 253 } 254 255#ifndef HAVE_CYGWIN 256 /* Try restoration of UID if changed (test clearing of saved uid) */ 257 if (old_uid != pw->pw_uid && 258 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 259 fatal("%s: was able to restore old [e]uid", __func__); 260#endif 261 262 /* Verify UID drop was successful */ 263 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 264 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 265 __func__, (u_int)getuid(), (u_int)geteuid(), 266 (u_int)pw->pw_uid); 267 } 268} 269