uidswap.c

   1 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */
   2 /*
   3  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   5  *                    All rights reserved
   6  * Code for uid-swapping.
   7  *
   8  * As far as I am concerned, the code I have written for this software
   9  * can be used freely for any purpose.  Any derived versions of this
  10  * software must be clearly marked as such, and if the derived work is
  11  * incompatible with the protocol description in the RFC file, it must be
  12  * called by a name other than "ssh" or "Secure Shell".
  13  */
  14
  15 #include "includes.h"
  16
  17 #include <sys/param.h>
  18 #include <errno.h>
  19 #include <pwd.h>
  20 #include <string.h>
  21 #include <unistd.h>
  22 #include <stdarg.h>
  23
  24 #include <grp.h>
  25
  26 #include "log.h"
  27 #include "uidswap.h"
  28 #include "xmalloc.h"
  29
  30 /*
  31  * Note: all these functions must work in all of the following cases:
  32  *    1. euid=0, ruid=0
  33  *    2. euid=0, ruid!=0
  34  *    3. euid!=0, ruid!=0
  35  * Additionally, they must work regardless of whether the system has
  36  * POSIX saved uids or not.
  37  */
  38
  39 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
  40 /* Lets assume that posix saved ids also work with seteuid, even though that
  41    is not part of the posix specification. */
  42 #define SAVED_IDS_WORK_WITH_SETEUID
  43 /* Saved effective uid. */
  44 static uid_t    saved_euid = 0;
  45 static gid_t    saved_egid = 0;
  46 #endif
  47
  48 /* Saved effective uid. */
  49 static int      privileged = 0;
  50 static int      temporarily_use_uid_effective = 0;
  51 static gid_t    *saved_egroups = NULL, *user_groups = NULL;
  52 static int      saved_egroupslen = -1, user_groupslen = -1;
  53
  54 /*
  55  * Temporarily changes to the given uid.  If the effective user
  56  * id is not root, this does nothing.  This call cannot be nested.
  57  */
  58 void
  59 temporarily_use_uid(struct passwd *pw)
  60 {
  61         /* Save the current euid, and egroups. */
  62 #ifdef SAVED_IDS_WORK_WITH_SETEUID
  63         saved_euid = geteuid();
  64         saved_egid = getegid();
  65         debug("temporarily_use_uid: %u/%u (e=%u/%u)",
  66             (u_int)pw->pw_uid, (u_int)pw->pw_gid,
  67             (u_int)saved_euid, (u_int)saved_egid);
  68 #ifndef HAVE_CYGWIN
  69         if (saved_euid != 0) {
  70                 privileged = 0;
  71                 return;
  72         }
  73 #endif
  74 #else
  75         if (geteuid() != 0) {
  76                 privileged = 0;
  77                 return;
  78         }
  79 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  80
  81         privileged = 1;
  82         temporarily_use_uid_effective = 1;
  83
  84         saved_egroupslen = getgroups(0, NULL);
  85         if (saved_egroupslen < 0)
  86                 fatal("getgroups: %.100s", strerror(errno));
  87         if (saved_egroupslen > 0) {
  88                 saved_egroups = xrealloc(saved_egroups,
  89                     saved_egroupslen, sizeof(gid_t));
  90                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  91                         fatal("getgroups: %.100s", strerror(errno));
  92         } else { /* saved_egroupslen == 0 */
  93                 if (saved_egroups != NULL)
  94                         xfree(saved_egroups);
  95         }
  96
  97         /* set and save the user's groups */
  98         if (user_groupslen == -1) {
  99                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
 100                         fatal("initgroups: %s: %.100s", pw->pw_name,
 101                             strerror(errno));
 102
 103                 user_groupslen = getgroups(0, NULL);
 104                 if (user_groupslen < 0)
 105                         fatal("getgroups: %.100s", strerror(errno));
 106                 if (user_groupslen > 0) {
 107                         user_groups = xrealloc(user_groups,
 108                             user_groupslen, sizeof(gid_t));
 109                         if (getgroups(user_groupslen, user_groups) < 0)
 110                                 fatal("getgroups: %.100s", strerror(errno));
 111                 } else { /* user_groupslen == 0 */
 112                         if (user_groups)
 113                                 xfree(user_groups);
 114                 }
 115         }
 116         /* Set the effective uid to the given (unprivileged) uid. */
 117         if (setgroups(user_groupslen, user_groups) < 0)
 118                 fatal("setgroups: %.100s", strerror(errno));
 119 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 120         /* Propagate the privileged gid to all of our gids. */
 121         if (setgid(getegid()) < 0)
 122                 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 123         /* Propagate the privileged uid to all of our uids. */
 124         if (setuid(geteuid()) < 0)
 125                 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 126 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 127         if (setegid(pw->pw_gid) < 0)
 128                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 129                     strerror(errno));
 130         if (seteuid(pw->pw_uid) == -1)
 131                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 132                     strerror(errno));
 133 }
 134
 135 void
 136 permanently_drop_suid(uid_t uid)
 137 {
 138         uid_t old_uid = getuid();
 139
 140         debug("permanently_drop_suid: %u", (u_int)uid);
 141 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 142         if (setresuid(uid, uid, uid) < 0)
 143                 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
 144 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 145         if (setreuid(uid, uid) < 0)
 146                 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
 147 #else
 148 # ifndef SETEUID_BREAKS_SETUID
 149         if (seteuid(uid) < 0)
 150                 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
 151 # endif
 152         if (setuid(uid) < 0)
 153                 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
 154 #endif
 155
 156 #ifndef HAVE_CYGWIN
 157         /* Try restoration of UID if changed (test clearing of saved uid) */
 158         if (old_uid != uid &&
 159             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 160                 fatal("%s: was able to restore old [e]uid", __func__);
 161 #endif
 162
 163         /* Verify UID drop was successful */
 164         if (getuid() != uid || geteuid() != uid) {
 165                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 166                     __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
 167         }
 168 }
 169
 170 /*
 171  * Restores to the original (privileged) uid.
 172  */
 173 void
 174 restore_uid(void)
 175 {
 176         /* it's a no-op unless privileged */
 177         if (!privileged) {
 178                 debug("restore_uid: (unprivileged)");
 179                 return;
 180         }
 181         if (!temporarily_use_uid_effective)
 182                 fatal("restore_uid: temporarily_use_uid not effective");
 183
 184 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 185         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 186         /* Set the effective uid back to the saved privileged uid. */
 187         if (seteuid(saved_euid) < 0)
 188                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 189         if (setegid(saved_egid) < 0)
 190                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 191 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 192         /*
 193          * We are unable to restore the real uid to its unprivileged value.
 194          * Propagate the real uid (usually more privileged) to effective uid
 195          * as well.
 196          */
 197         setuid(getuid());
 198         setgid(getgid());
 199 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 200
 201         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 202                 fatal("setgroups: %.100s", strerror(errno));
 203         temporarily_use_uid_effective = 0;
 204 }
 205
 206 /*
 207  * Permanently sets all uids to the given uid.  This cannot be
 208  * called while temporarily_use_uid is effective.
 209  */
 210 void
 211 permanently_set_uid(struct passwd *pw)
 212 {
 213         uid_t old_uid = getuid();
 214         gid_t old_gid = getgid();
 215
 216         if (pw == NULL)
 217                 fatal("permanently_set_uid: no user given");
 218         if (temporarily_use_uid_effective)
 219                 fatal("permanently_set_uid: temporarily_use_uid effective");
 220         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 221             (u_int)pw->pw_gid);
 222
 223 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
 224         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 225                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 226 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
 227         if (setregid(pw->pw_gid, pw->pw_gid) < 0)
 228                 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 229 #else
 230         if (setegid(pw->pw_gid) < 0)
 231                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 232         if (setgid(pw->pw_gid) < 0)
 233                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 234 #endif
 235
 236 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 237         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 238                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 239 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 240         if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
 241                 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 242 #else
 243 # ifndef SETEUID_BREAKS_SETUID
 244         if (seteuid(pw->pw_uid) < 0)
 245                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 246 # endif
 247         if (setuid(pw->pw_uid) < 0)
 248                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 249 #endif
 250
 251 #ifndef HAVE_CYGWIN
 252         /* Try restoration of GID if changed (test clearing of saved gid) */
 253         if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 254             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 255                 fatal("%s: was able to restore old [e]gid", __func__);
 256 #endif
 257
 258         /* Verify GID drop was successful */
 259         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 260                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 261                     __func__, (u_int)getgid(), (u_int)getegid(),
 262                     (u_int)pw->pw_gid);
 263         }
 264
 265 #ifndef HAVE_CYGWIN
 266         /* Try restoration of UID if changed (test clearing of saved uid) */
 267         if (old_uid != pw->pw_uid &&
 268             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 269                 fatal("%s: was able to restore old [e]uid", __func__);
 270 #endif
 271
 272         /* Verify UID drop was successful */
 273         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 274                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 275                     __func__, (u_int)getuid(), (u_int)geteuid(),
 276                     (u_int)pw->pw_uid);
 277         }
 278 }