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