uidswap.c revision 255767
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 free(saved_egroups); 94 } 95 96 /* set and save the user's groups */ 97 if (user_groupslen == -1) { 98 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 99 fatal("initgroups: %s: %.100s", pw->pw_name, 100 strerror(errno)); 101 102 user_groupslen = getgroups(0, NULL); 103 if (user_groupslen < 0) 104 fatal("getgroups: %.100s", strerror(errno)); 105 if (user_groupslen > 0) { 106 user_groups = xrealloc(user_groups, 107 user_groupslen, sizeof(gid_t)); 108 if (getgroups(user_groupslen, user_groups) < 0) 109 fatal("getgroups: %.100s", strerror(errno)); 110 } else { /* user_groupslen == 0 */ 111 free(user_groups); 112 } 113 } 114 /* Set the effective uid to the given (unprivileged) uid. */ 115 if (setgroups(user_groupslen, user_groups) < 0) 116 fatal("setgroups: %.100s", strerror(errno)); 117#ifndef SAVED_IDS_WORK_WITH_SETEUID 118 /* Propagate the privileged gid to all of our gids. */ 119 if (setgid(getegid()) < 0) 120 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 121 /* Propagate the privileged uid to all of our uids. */ 122 if (setuid(geteuid()) < 0) 123 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 124#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 125 if (setegid(pw->pw_gid) < 0) 126 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 127 strerror(errno)); 128 if (seteuid(pw->pw_uid) == -1) 129 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 130 strerror(errno)); 131} 132 133void 134permanently_drop_suid(uid_t uid) 135{ 136 uid_t old_uid = getuid(); 137 138 debug("permanently_drop_suid: %u", (u_int)uid); 139 if (setresuid(uid, uid, uid) < 0) 140 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno)); 141 142#ifndef HAVE_CYGWIN 143 /* Try restoration of UID if changed (test clearing of saved uid) */ 144 if (old_uid != uid && 145 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 146 fatal("%s: was able to restore old [e]uid", __func__); 147#endif 148 149 /* Verify UID drop was successful */ 150 if (getuid() != uid || geteuid() != uid) { 151 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 152 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid); 153 } 154} 155 156/* 157 * Restores to the original (privileged) uid. 158 */ 159void 160restore_uid(void) 161{ 162 /* it's a no-op unless privileged */ 163 if (!privileged) { 164 debug("restore_uid: (unprivileged)"); 165 return; 166 } 167 if (!temporarily_use_uid_effective) 168 fatal("restore_uid: temporarily_use_uid not effective"); 169 170#ifdef SAVED_IDS_WORK_WITH_SETEUID 171 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 172 /* Set the effective uid back to the saved privileged uid. */ 173 if (seteuid(saved_euid) < 0) 174 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 175 if (setegid(saved_egid) < 0) 176 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 177#else /* SAVED_IDS_WORK_WITH_SETEUID */ 178 /* 179 * We are unable to restore the real uid to its unprivileged value. 180 * Propagate the real uid (usually more privileged) to effective uid 181 * as well. 182 */ 183 setuid(getuid()); 184 setgid(getgid()); 185#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 186 187 if (setgroups(saved_egroupslen, saved_egroups) < 0) 188 fatal("setgroups: %.100s", strerror(errno)); 189 temporarily_use_uid_effective = 0; 190} 191 192/* 193 * Permanently sets all uids to the given uid. This cannot be 194 * called while temporarily_use_uid is effective. 195 */ 196void 197permanently_set_uid(struct passwd *pw) 198{ 199 uid_t old_uid = getuid(); 200 gid_t old_gid = getgid(); 201 202 if (pw == NULL) 203 fatal("permanently_set_uid: no user given"); 204 if (temporarily_use_uid_effective) 205 fatal("permanently_set_uid: temporarily_use_uid effective"); 206 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 207 (u_int)pw->pw_gid); 208 209 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 210 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 211 212#ifdef __APPLE__ 213 /* 214 * OS X requires initgroups after setgid to opt back into 215 * memberd support for >16 supplemental groups. 216 */ 217 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 218 fatal("initgroups %.100s %u: %.100s", 219 pw->pw_name, (u_int)pw->pw_gid, strerror(errno)); 220#endif 221 222 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 223 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 224 225#ifndef HAVE_CYGWIN 226 /* Try restoration of GID if changed (test clearing of saved gid) */ 227 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 228 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 229 fatal("%s: was able to restore old [e]gid", __func__); 230#endif 231 232 /* Verify GID drop was successful */ 233 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 234 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 235 __func__, (u_int)getgid(), (u_int)getegid(), 236 (u_int)pw->pw_gid); 237 } 238 239#ifndef HAVE_CYGWIN 240 /* Try restoration of UID if changed (test clearing of saved uid) */ 241 if (old_uid != pw->pw_uid && 242 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 243 fatal("%s: was able to restore old [e]uid", __func__); 244#endif 245 246 /* Verify UID drop was successful */ 247 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 248 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 249 __func__, (u_int)getuid(), (u_int)geteuid(), 250 (u_int)pw->pw_uid); 251 } 252} 253