uidswap.c revision 124208
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" 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 20/* 21 * Note: all these functions must work in all of the following cases: 22 * 1. euid=0, ruid=0 23 * 2. euid=0, ruid!=0 24 * 3. euid!=0, ruid!=0 25 * Additionally, they must work regardless of whether the system has 26 * POSIX saved uids or not. 27 */ 28 29#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 30/* Lets assume that posix saved ids also work with seteuid, even though that 31 is not part of the posix specification. */ 32#define SAVED_IDS_WORK_WITH_SETEUID 33/* Saved effective uid. */ 34static uid_t saved_euid = 0; 35static gid_t saved_egid = 0; 36#endif 37 38/* Saved effective uid. */ 39static int privileged = 0; 40static int temporarily_use_uid_effective = 0; 41static gid_t saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX]; 42static int saved_egroupslen = -1, user_groupslen = -1; 43 44/* 45 * Temporarily changes to the given uid. If the effective user 46 * id is not root, this does nothing. This call cannot be nested. 47 */ 48void 49temporarily_use_uid(struct passwd *pw) 50{ 51 /* Save the current euid, and egroups. */ 52#ifdef SAVED_IDS_WORK_WITH_SETEUID 53 saved_euid = geteuid(); 54 saved_egid = getegid(); 55 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 56 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 57 (u_int)saved_euid, (u_int)saved_egid); 58 if (saved_euid != 0) { 59 privileged = 0; 60 return; 61 } 62#else 63 if (geteuid() != 0) { 64 privileged = 0; 65 return; 66 } 67#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 68 69 privileged = 1; 70 temporarily_use_uid_effective = 1; 71 saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups); 72 if (saved_egroupslen < 0) 73 fatal("getgroups: %.100s", strerror(errno)); 74 75 /* set and save the user's groups */ 76 if (user_groupslen == -1) { 77 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 78 fatal("initgroups: %s: %.100s", pw->pw_name, 79 strerror(errno)); 80 user_groupslen = getgroups(NGROUPS_MAX, user_groups); 81 if (user_groupslen < 0) 82 fatal("getgroups: %.100s", strerror(errno)); 83 } 84 /* Set the effective uid to the given (unprivileged) uid. */ 85 if (setgroups(user_groupslen, user_groups) < 0) 86 fatal("setgroups: %.100s", strerror(errno)); 87#ifndef SAVED_IDS_WORK_WITH_SETEUID 88 /* Propagate the privileged gid to all of our gids. */ 89 if (setgid(getegid()) < 0) 90 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 91 /* Propagate the privileged uid to all of our uids. */ 92 if (setuid(geteuid()) < 0) 93 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 94#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 95 if (setegid(pw->pw_gid) < 0) 96 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, 97 strerror(errno)); 98 if (seteuid(pw->pw_uid) == -1) 99 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 100 strerror(errno)); 101} 102 103/* 104 * Restores to the original (privileged) uid. 105 */ 106void 107restore_uid(void) 108{ 109 /* it's a no-op unless privileged */ 110 if (!privileged) { 111 debug("restore_uid: (unprivileged)"); 112 return; 113 } 114 if (!temporarily_use_uid_effective) 115 fatal("restore_uid: temporarily_use_uid not effective"); 116 117#ifdef SAVED_IDS_WORK_WITH_SETEUID 118 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 119 /* Set the effective uid back to the saved privileged uid. */ 120 if (seteuid(saved_euid) < 0) 121 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 122 if (setegid(saved_egid) < 0) 123 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 124#else /* SAVED_IDS_WORK_WITH_SETEUID */ 125 /* 126 * We are unable to restore the real uid to its unprivileged value. 127 * Propagate the real uid (usually more privileged) to effective uid 128 * as well. 129 */ 130 setuid(getuid()); 131 setgid(getgid()); 132#endif /* SAVED_IDS_WORK_WITH_SETEUID */ 133 134 if (setgroups(saved_egroupslen, saved_egroups) < 0) 135 fatal("setgroups: %.100s", strerror(errno)); 136 temporarily_use_uid_effective = 0; 137} 138 139/* 140 * Permanently sets all uids to the given uid. This cannot be 141 * called while temporarily_use_uid is effective. 142 */ 143void 144permanently_set_uid(struct passwd *pw) 145{ 146 uid_t old_uid = getuid(); 147 gid_t old_gid = getgid(); 148 149 if (temporarily_use_uid_effective) 150 fatal("permanently_set_uid: temporarily_use_uid effective"); 151 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid, 152 (u_int)pw->pw_gid); 153 154#if defined(HAVE_SETRESGID) 155 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0) 156 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 157#elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID) 158 if (setregid(pw->pw_gid, pw->pw_gid) < 0) 159 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 160#else 161 if (setegid(pw->pw_gid) < 0) 162 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 163 if (setgid(pw->pw_gid) < 0) 164 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 165#endif 166 167#if defined(HAVE_SETRESUID) 168 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0) 169 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 170#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID) 171 if (setreuid(pw->pw_uid, pw->pw_uid) < 0) 172 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 173#else 174# ifndef SETEUID_BREAKS_SETUID 175 if (seteuid(pw->pw_uid) < 0) 176 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 177# endif 178 if (setuid(pw->pw_uid) < 0) 179 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 180#endif 181 182 /* Try restoration of GID if changed (test clearing of saved gid) */ 183 if (old_gid != pw->pw_gid && 184 (setgid(old_gid) != -1 || setegid(old_gid) != -1)) 185 fatal("%s: was able to restore old [e]gid", __func__); 186 187 /* Verify GID drop was successful */ 188 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) { 189 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)", 190 __func__, (u_int)getgid(), (u_int)getegid(), 191 (u_int)pw->pw_gid); 192 } 193 194#ifndef HAVE_CYGWIN 195 /* Try restoration of UID if changed (test clearing of saved uid) */ 196 if (old_uid != pw->pw_uid && 197 (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) 198 fatal("%s: was able to restore old [e]uid", __func__); 199#endif 200 201 /* Verify UID drop was successful */ 202 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) { 203 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)", 204 __func__, (u_int)getuid(), (u_int)geteuid(), 205 (u_int)pw->pw_uid); 206 } 207} 208