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 * Copyright 2009 Sun Microsystems, Inc. All rights reserved. 15 * Use is subject to license terms. 16 */ 17 18 #include "includes.h" 19 RCSID("$OpenBSD: uidswap.c,v 1.23 2002/07/15 17:15:31 stevesk Exp $"); 20 21 #include <priv.h> 22 23 #include "log.h" 24 #include "uidswap.h" 25 #include "buffer.h" 26 #include "servconf.h" 27 28 /* 29 * Note: all these functions must work in all of the following cases: 30 * 1. euid=0, ruid=0 31 * 2. euid=0, ruid!=0 32 * 3. euid!=0, ruid!=0 33 * Additionally, they must work regardless of whether the system has 34 * POSIX saved uids or not. 35 */ 36 37 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS) 38 /* Lets assume that posix saved ids also work with seteuid, even though that 39 is not part of the posix specification. */ 40 #define SAVED_IDS_WORK 41 /* Saved effective uid. */ 42 static uid_t saved_euid = 0; 43 static gid_t saved_egid = 0; 44 #endif 45 46 /* Saved effective uid. */ 47 static int privileged = 0; 48 static int temporarily_use_uid_effective = 0; 49 static int ngroups_max = -1; 50 static gid_t *saved_egroups, *user_groups; 51 static int saved_egroupslen = -1, user_groupslen = -1; 52 53 /* 54 * Temporarily changes to the given uid. If the effective user 55 * id is not root, this does nothing. This call cannot be nested. 56 */ 57 void 58 temporarily_use_uid(struct passwd *pw) 59 { 60 /* Save the current euid, and egroups. */ 61 #ifdef SAVED_IDS_WORK 62 saved_euid = geteuid(); 63 saved_egid = getegid(); 64 debug("temporarily_use_uid: %u/%u (e=%u/%u)", 65 (u_int)pw->pw_uid, (u_int)pw->pw_gid, 66 (u_int)saved_euid, (u_int)saved_egid); 67 if (saved_euid != 0) { 68 privileged = 0; 69 return; 70 } 71 #else 72 if (geteuid() != 0) { 73 privileged = 0; 74 return; 75 } 76 #endif /* SAVED_IDS_WORK */ 77 78 privileged = 1; 79 temporarily_use_uid_effective = 1; 80 81 if (ngroups_max < 0) { 82 ngroups_max = sysconf(_SC_NGROUPS_MAX); 83 saved_egroups = malloc(ngroups_max * sizeof (gid_t)); 84 user_groups = malloc(ngroups_max * sizeof (gid_t)); 85 if (saved_egroups == NULL || user_groups == NULL) 86 fatal("malloc(gid array): %.100s", strerror(errno)); 87 } 88 89 saved_egroupslen = getgroups(ngroups_max, saved_egroups); 90 if (saved_egroupslen < 0) 91 fatal("getgroups: %.100s", strerror(errno)); 92 93 /* set and save the user's groups */ 94 if (user_groupslen == -1) { 95 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 96 fatal("initgroups: %s: %.100s", pw->pw_name, 97 strerror(errno)); 98 user_groupslen = getgroups(ngroups_max, user_groups); 99 if (user_groupslen < 0) 100 fatal("getgroups: %.100s", strerror(errno)); 101 } 102 /* Set the effective uid to the given (unprivileged) uid. */ 103 if (setgroups(user_groupslen, user_groups) < 0) 104 fatal("setgroups: %.100s", strerror(errno)); 105 #ifdef SAVED_IDS_WORK 106 /* Set saved gid and set real gid */ 107 if (setregid(pw->pw_gid, -1) == -1) 108 debug("setregid(%u, -1): %.100s", (uint_t)pw->pw_gid, strerror(errno)); 109 /* Set saved uid and set real uid */ 110 if (setreuid(pw->pw_uid, -1) == -1) 111 debug("setreuid(%u, -1): %.100s", (uint_t)pw->pw_uid, strerror(errno)); 112 #else 113 /* Propagate the privileged gid to all of our gids. */ 114 if (setgid(getegid()) < 0) 115 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno)); 116 /* Propagate the privileged uid to all of our uids. */ 117 if (setuid(geteuid()) < 0) 118 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno)); 119 #endif /* SAVED_IDS_WORK */ 120 /* Set effective gid */ 121 if (setegid(pw->pw_gid) == -1) 122 fatal("setegid %u: %.100s", (u_int)pw->pw_uid, 123 strerror(errno)); 124 /* Set effective uid */ 125 if (seteuid(pw->pw_uid) == -1) 126 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, 127 strerror(errno)); 128 /* 129 * If saved set ids work then 130 * 131 * ruid == euid == pw->pw_uid 132 * saved uid = previous euid 133 * rgid == egid == pw->pw_gid 134 * saved gid = previous egid 135 */ 136 } 137 138 /* 139 * Restores to the original (privileged) uid. 140 */ 141 void 142 restore_uid(void) 143 { 144 /* it's a no-op unless privileged */ 145 if (!privileged) { 146 debug("restore_uid: (unprivileged)"); 147 return; 148 } 149 if (!temporarily_use_uid_effective) 150 fatal("restore_uid: temporarily_use_uid not effective"); 151 152 #ifdef SAVED_IDS_WORK 153 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid); 154 /* Set the effective uid back to the saved privileged uid. */ 155 if (seteuid(saved_euid) < 0) 156 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 157 if (setuid(saved_euid) < 0) 158 fatal("setuid %u: %.100s", (u_int)saved_euid, strerror(errno)); 159 if (setegid(saved_egid) < 0) 160 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno)); 161 if (setgid(saved_egid) < 0) 162 fatal("setgid %u: %.100s", (u_int)saved_egid, strerror(errno)); 163 #else /* SAVED_IDS_WORK */ 164 /* 165 * We are unable to restore the real uid to its unprivileged value. 166 * Propagate the real uid (usually more privileged) to effective uid 167 * as well. 168 */ 169 setuid(getuid()); 170 setgid(getgid()); 171 #endif /* SAVED_IDS_WORK */ 172 173 if (setgroups(saved_egroupslen, saved_egroups) < 0) 174 fatal("setgroups: %.100s", strerror(errno)); 175 temporarily_use_uid_effective = 0; 176 } 177 178 /* 179 * Permanently sets all uids to the given uid. This cannot be called while 180 * temporarily_use_uid is effective. Note that when the ChrootDirectory option 181 * is in use we keep a few privileges so that we can call chroot(2) later while 182 * already running under UIDs of a connecting user. 183 */ 184 void 185 permanently_set_uid(struct passwd *pw, char *chroot_directory) 186 { 187 priv_set_t *pset; 188 189 if (temporarily_use_uid_effective) 190 fatal("%s: temporarily_use_uid effective", __func__); 191 192 debug("%s: %u/%u", __func__, (u_int)pw->pw_uid, (u_int)pw->pw_gid); 193 194 if (initgroups(pw->pw_name, pw->pw_gid) < 0) 195 fatal("initgroups: %s: %.100s", pw->pw_name, 196 strerror(errno)); 197 198 if (setgid(pw->pw_gid) < 0) 199 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno)); 200 201 /* 202 * If root is connecting we are done now. Note that we must have called 203 * setgid() in case that the SSH server was run under a group other than 204 * root. 205 */ 206 if (pw->pw_uid == 0) 207 return; 208 209 /* 210 * This means we will keep all privileges after the UID change. 211 */ 212 if (setpflags(PRIV_AWARE, 1) != 0) 213 fatal("setpflags: %s", strerror(errno)); 214 215 /* Now we are running under UID of the user. */ 216 if (setuid(pw->pw_uid) < 0) 217 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno)); 218 219 /* 220 * We will run with the privileges from the Inheritable set as 221 * we would have after exec(2) if we had stayed in NPA mode 222 * before setuid(2) call (see privileges(5), user_attr(4), and 223 * pam_unix_cred(5)). We want to run with P = E = I, with I as 224 * set by pam_unix_cred(5). We also add PRIV_PROC_CHROOT, 225 * obviously, and then PRIV_PROC_FORK and PRIV_PROC_EXEC, since 226 * those two might have been removed from the I set. Note that 227 * we are expected to finish the login process without them in 228 * the I set, the important thing is that those not be passed on 229 * to a shell or a subsystem later if they were not set in 230 * pam_unix_cred(5). 231 */ 232 if ((pset = priv_allocset()) == NULL) 233 fatal("priv_allocset: %s", strerror(errno)); 234 if (getppriv(PRIV_INHERITABLE, pset) != 0) 235 fatal("getppriv: %s", strerror(errno)); 236 237 /* We do not need PRIV_PROC_CHROOT unless chroot()ing. */ 238 if (chroot_requested(chroot_directory) && 239 priv_addset(pset, PRIV_PROC_CHROOT) == -1) { 240 fatal("%s: priv_addset failed", __func__); 241 } 242 243 if (priv_addset(pset, PRIV_PROC_FORK) == -1 || 244 priv_addset(pset, PRIV_PROC_EXEC) == -1) { 245 fatal("%s: priv_addset failed", __func__); 246 } 247 248 /* Set only P; this will also set E. */ 249 if (setppriv(PRIV_SET, PRIV_PERMITTED, pset) == -1) 250 fatal("setppriv: %s", strerror(errno)); 251 252 /* We don't need the PA flag anymore. */ 253 if (setpflags(PRIV_AWARE, 0) == -1) 254 fatal("setpflags: %s", strerror(errno)); 255 256 priv_freeset(pset); 257 } 258