uidswap.c revision 146998
1268896Sbapt/* 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" 15RCSID("$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. */ 35static uid_t saved_euid = 0; 36static gid_t saved_egid = 0; 37#endif 38 39/* Saved effective uid. */ 40static int privileged = 0; 41static int temporarily_use_uid_effective = 0; 42static gid_t *saved_egroups = NULL, *user_groups = NULL; 43static 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 */ 49void 50temporarily_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#ifndef HAVE_CYGWIN 60 if (saved_euid != 0) { 61 privileged = 0; 62 return; 63 } 64#endif 65#else 66 if (geteuid() != 0) { 67 privileged = 0; 68 return; 69 } 70#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 71 72 privileged = 1; 73 temporarily_use_uid_effective = 1; 74 75 saved_egroupslen = getgroups(0, NULL); 76 if (saved_egroupslen < 0) 77 fatal("getgroups: %.100s", strerror(errno)); 78 if (saved_egroupslen > 0) { 79 saved_egroups = xrealloc(saved_egroups, 80 saved_egroupslen * sizeof(gid_t)); 81 if (getgroups(saved_egroupslen, saved_egroups) < 0) 82 fatal("getgroups: %.100s", strerror(errno)); 83 } else { /* saved_egroupslen == 0 */ 84 if (saved_egroups != NULL) 85 xfree(saved_egroups); 86 } 87 88 /* set and save the user's groups */ 89 if (user_groupslen == -1) { 90 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 91 fatal("initgroups: %s: %.100s", pw->pw_name, 92 strerror(errno)); 93 94 user_groupslen = getgroups(0, NULL); 95 if (user_groupslen < 0) 96 fatal("getgroups: %.100s", strerror(errno)); 97 if (user_groupslen > 0) { 98 user_groups = xrealloc(user_groups, 99 user_groupslen * sizeof(gid_t)); 100 if (getgroups(user_groupslen, user_groups) < 0) 101 fatal("getgroups: %.100s", strerror(errno)); 102 } else { /* user_groupslen == 0 */ 103 if (user_groups) 104 xfree(user_groups); 105 } 106 } 107 /* Set the effective uid to the given (unprivileged) uid. */ 108 if (setgroups(user_groupslen, user_groups) < 0) 109 fatal("setgroups: %.100s", strerror(errno)); 110#ifndef SAVED_IDS_WORK_WITH_SETEUID 111 /* Propagate the privileged gid to all of our gids. */ 112 if (setgid(getegid()) < 0) 113 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 114 /* Propagate the privileged uid to all of our uids. */ 115 if (setuid(geteuid()) < 0) 116 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 117#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 118 if (setegid(pw->pw_gid) < 0) 119 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 120 strerror(errno)); 121 if (seteuid(pw->pw_uid) == -1) 122 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 123 strerror(errno)); 124} 125 126/* 127 * Restores to the original (privileged) uid. 128 */ 129void 130restore_uid(void) 131{ 132 /* it's a no-op unless privileged */ 133 if (!privileged) { 134 debug("restore_uid: (unprivileged)"); 135 return; 136 } 137 if (!temporarily_use_uid_effective) 138 fatal("restore_uid: temporarily_use_uid not effective"); 139 140#ifdef SAVED_IDS_WORK_WITH_SETEUID 141 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 142 /* Set the effective uid back to the saved privileged uid. */ 143 if (seteuid(saved_euid) < 0) 144 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 145 if (setegid(saved_egid) < 0) 146 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 147#else /* SAVED_IDS_WORK_WITH_SETEUID */ 148 /* 149 * We are unable to restore the real uid to its unprivileged value. 150 * Propagate the real uid (usually more privileged) to effective uid 151 * as well. 152 */ 153 setuid(getuid()); 154 setgid(getgid()); 155#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 156 157 if (setgroups(saved_egroupslen, saved_egroups) < 0) 158 fatal("setgroups: %.100s", strerror(errno)); 159 temporarily_use_uid_effective = 0; 160} 161 162/* 163 * Permanently sets all uids to the given uid. This cannot be 164 * called while temporarily_use_uid is effective. 165 */ 166void 167permanently_set_uid(struct passwd *pw) 168{ 169 uid_t old_uid = getuid(); 170 gid_t old_gid = getgid(); 171 172 if (temporarily_use_uid_effective) 173 fatal("permanently_set_uid: temporarily_use_uid effective"); 174 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 175 (u_int)pw->pw_gid); 176 177#if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID) 178 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 179 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 180#elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 181 if (setregid(pw->pw_gid, pw->pw_gid) < 0) 182 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 183#else 184 if (setegid(pw->pw_gid) < 0) 185 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 186 if (setgid(pw->pw_gid) < 0) 187 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 188#endif 189 190#if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID) 191 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 192 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 193#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 194 if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 195 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 196#else 197# ifndef SETEUID_BREAKS_SETUID 198 if (seteuid(pw->pw_uid) < 0) 199 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 200# endif 201 if (setuid(pw->pw_uid) < 0) 202 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 203#endif 204 205#ifndef HAVE_CYGWIN 206 /* Try restoration of GID if changed (test clearing of saved gid) */ 207 if (old_gid != pw->pw_gid && pw->pw_uid != 0 && 208 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 209 fatal("%s: was able to restore old [e]gid", __func__); 210#endif 211 212 /* Verify GID drop was successful */ 213 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 214 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 215 __func__, (u_int)getgid(), (u_int)getegid(), 216 (u_int)pw->pw_gid); 217 } 218 219#ifndef HAVE_CYGWIN 220 /* Try restoration of UID if changed (test clearing of saved uid) */ 221 if (old_uid != pw->pw_uid && 222 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 223 fatal("%s: was able to restore old [e]uid", __func__); 224#endif 225 226 /* Verify UID drop was successful */ 227 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 228 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 229 __func__, (u_int)getuid(), (u_int)geteuid(), 230 (u_int)pw->pw_uid); 231 } 232} 233