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