uidswap.c

   1 /* $OpenBSD: uidswap.c,v 1.32 2006/07/17 01:31:10 stevesk 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/types.h>
  18
  19 #include <errno.h>
  20 #include <pwd.h>
  21 #include <unistd.h>
  22
  23 #include <grp.h>
  24
  25 #include "log.h"
  26 #include "uidswap.h"
  27 #include "xmalloc.h"
  28
  29 /*
  30  * Note: all these functions must work in all of the following cases:
  31  *    1. euid=0, ruid=0
  32  *    2. euid=0, ruid!=0
  33  *    3. euid!=0, ruid!=0
  34  * Additionally, they must work regardless of whether the system has
  35  * POSIX saved uids or not.
  36  */
  37
  38 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
  39 /* Lets assume that posix saved ids also work with seteuid, even though that
  40    is not part of the posix specification. */
  41 #define SAVED_IDS_WORK_WITH_SETEUID
  42 /* Saved effective uid. */
  43 static uid_t    saved_euid = 0;
  44 static gid_t    saved_egid = 0;
  45 #endif
  46
  47 /* Saved effective uid. */
  48 static int      privileged = 0;
  49 static int      temporarily_use_uid_effective = 0;
  50 static gid_t    *saved_egroups = NULL, *user_groups = NULL;
  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_WITH_SETEUID
  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 #ifndef HAVE_CYGWIN
  68         if (saved_euid != 0) {
  69                 privileged = 0;
  70                 return;
  71         }
  72 #endif
  73 #else
  74         if (geteuid() != 0) {
  75                 privileged = 0;
  76                 return;
  77         }
  78 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  79
  80         privileged = 1;
  81         temporarily_use_uid_effective = 1;
  82
  83         saved_egroupslen = getgroups(0, NULL);
  84         if (saved_egroupslen < 0)
  85                 fatal("getgroups: %.100s", strerror(errno));
  86         if (saved_egroupslen > 0) {
  87                 saved_egroups = xrealloc(saved_egroups,
  88                     saved_egroupslen, sizeof(gid_t));
  89                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  90                         fatal("getgroups: %.100s", strerror(errno));
  91         } else { /* saved_egroupslen == 0 */
  92                 if (saved_egroups != NULL)
  93                         xfree(saved_egroups);
  94         }
  95
  96         /* set and save the user's groups */
  97         if (user_groupslen == -1) {
  98                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
  99                         fatal("initgroups: %s: %.100s", pw->pw_name,
 100                             strerror(errno));
 101
 102                 user_groupslen = getgroups(0, NULL);
 103                 if (user_groupslen < 0)
 104                         fatal("getgroups: %.100s", strerror(errno));
 105                 if (user_groupslen > 0) {
 106                         user_groups = xrealloc(user_groups,
 107                             user_groupslen, sizeof(gid_t));
 108                         if (getgroups(user_groupslen, user_groups) < 0)
 109                                 fatal("getgroups: %.100s", strerror(errno));
 110                 } else { /* user_groupslen == 0 */
 111                         if (user_groups)
 112                                 xfree(user_groups);
 113                 }
 114         }
 115         /* Set the effective uid to the given (unprivileged) uid. */
 116         if (setgroups(user_groupslen, user_groups) < 0)
 117                 fatal("setgroups: %.100s", strerror(errno));
 118 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 119         /* Propagate the privileged gid to all of our gids. */
 120         if (setgid(getegid()) < 0)
 121                 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 122         /* Propagate the privileged uid to all of our uids. */
 123         if (setuid(geteuid()) < 0)
 124                 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 125 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 126         if (setegid(pw->pw_gid) < 0)
 127                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 128                     strerror(errno));
 129         if (seteuid(pw->pw_uid) == -1)
 130                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 131                     strerror(errno));
 132 }
 133
 134 void
 135 permanently_drop_suid(uid_t uid)
 136 {
 137         uid_t old_uid = getuid();
 138
 139         debug("permanently_drop_suid: %u", (u_int)uid);
 140 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 141         if (setresuid(uid, uid, uid) < 0)
 142                 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
 143 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 144         if (setreuid(uid, uid) < 0)
 145                 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
 146 #else
 147 # ifndef SETEUID_BREAKS_SETUID
 148         if (seteuid(uid) < 0)
 149                 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
 150 # endif
 151         if (setuid(uid) < 0)
 152                 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
 153 #endif
 154
 155 #ifndef HAVE_CYGWIN
 156         /* Try restoration of UID if changed (test clearing of saved uid) */
 157         if (old_uid != uid &&
 158             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 159                 fatal("%s: was able to restore old [e]uid", __func__);
 160 #endif
 161
 162         /* Verify UID drop was successful */
 163         if (getuid() != uid || geteuid() != uid) {
 164                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 165                     __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
 166         }
 167 }
 168
 169 /*
 170  * Restores to the original (privileged) uid.
 171  */
 172 void
 173 restore_uid(void)
 174 {
 175         /* it's a no-op unless privileged */
 176         if (!privileged) {
 177                 debug("restore_uid: (unprivileged)");
 178                 return;
 179         }
 180         if (!temporarily_use_uid_effective)
 181                 fatal("restore_uid: temporarily_use_uid not effective");
 182
 183 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 184         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 185         /* Set the effective uid back to the saved privileged uid. */
 186         if (seteuid(saved_euid) < 0)
 187                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 188         if (setegid(saved_egid) < 0)
 189                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 190 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 191         /*
 192          * We are unable to restore the real uid to its unprivileged value.
 193          * Propagate the real uid (usually more privileged) to effective uid
 194          * as well.
 195          */
 196         setuid(getuid());
 197         setgid(getgid());
 198 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 199
 200         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 201                 fatal("setgroups: %.100s", strerror(errno));
 202         temporarily_use_uid_effective = 0;
 203 }
 204
 205 /*
 206  * Permanently sets all uids to the given uid.  This cannot be
 207  * called while temporarily_use_uid is effective.
 208  */
 209 void
 210 permanently_set_uid(struct passwd *pw)
 211 {
 212         uid_t old_uid = getuid();
 213         gid_t old_gid = getgid();
 214
 215         if (pw == NULL)
 216                 fatal("permanently_set_uid: no user given");
 217         if (temporarily_use_uid_effective)
 218                 fatal("permanently_set_uid: temporarily_use_uid effective");
 219         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 220             (u_int)pw->pw_gid);
 221
 222 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
 223         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 224                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 225 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
 226         if (setregid(pw->pw_gid, pw->pw_gid) < 0)
 227                 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 228 #else
 229         if (setegid(pw->pw_gid) < 0)
 230                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 231         if (setgid(pw->pw_gid) < 0)
 232                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 233 #endif
 234
 235 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 236         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 237                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 238 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 239         if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
 240                 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 241 #else
 242 # ifndef SETEUID_BREAKS_SETUID
 243         if (seteuid(pw->pw_uid) < 0)
 244                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 245 # endif
 246         if (setuid(pw->pw_uid) < 0)
 247                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 248 #endif
 249
 250 #ifndef HAVE_CYGWIN
 251         /* Try restoration of GID if changed (test clearing of saved gid) */
 252         if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 253             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 254                 fatal("%s: was able to restore old [e]gid", __func__);
 255 #endif
 256
 257         /* Verify GID drop was successful */
 258         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 259                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 260                     __func__, (u_int)getgid(), (u_int)getegid(),
 261                     (u_int)pw->pw_gid);
 262         }
 263
 264 #ifndef HAVE_CYGWIN
 265         /* Try restoration of UID if changed (test clearing of saved uid) */
 266         if (old_uid != pw->pw_uid &&
 267             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 268                 fatal("%s: was able to restore old [e]uid", __func__);
 269 #endif
 270
 271         /* Verify UID drop was successful */
 272         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 273                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 274                     __func__, (u_int)getuid(), (u_int)geteuid(),
 275                     (u_int)pw->pw_uid);
 276         }
 277 }