uidswap.c

   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 #include "includes.h"
  15 RCSID("$OpenBSD: uidswap.c,v 1.24 2003/05/29 16:58:45 deraadt Exp $");
  16
  17 #include "log.h"
  18 #include "uidswap.h"
  19 #include "xmalloc.h"
  20
  21 /*
  22  * Note: all these functions must work in all of the following cases:
  23  *    1. euid=0, ruid=0
  24  *    2. euid=0, ruid!=0
  25  *    3. euid!=0, ruid!=0
  26  * Additionally, they must work regardless of whether the system has
  27  * POSIX saved uids or not.
  28  */
  29
  30 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
  31 /* Lets assume that posix saved ids also work with seteuid, even though that
  32    is not part of the posix specification. */
  33 #define SAVED_IDS_WORK_WITH_SETEUID
  34 /* Saved effective uid. */
  35 static uid_t    saved_euid = 0;
  36 static gid_t    saved_egid = 0;
  37 #endif
  38
  39 /* Saved effective uid. */
  40 static int      privileged = 0;
  41 static int      temporarily_use_uid_effective = 0;
  42 static gid_t    *saved_egroups = NULL, *user_groups = NULL;
  43 static int      saved_egroupslen = -1, user_groupslen = -1;
  44
  45 /*
  46  * Temporarily changes to the given uid.  If the effective user
  47  * id is not root, this does nothing.  This call cannot be nested.
  48  */
  49 void
  50 temporarily_use_uid(struct passwd *pw)
  51 {
  52         /* Save the current euid, and egroups. */
  53 #ifdef SAVED_IDS_WORK_WITH_SETEUID
  54         saved_euid = geteuid();
  55         saved_egid = getegid();
  56         debug("temporarily_use_uid: %u/%u (e=%u/%u)",
  57             (u_int)pw->pw_uid, (u_int)pw->pw_gid,
  58             (u_int)saved_euid, (u_int)saved_egid);
  59 #ifndef HAVE_CYGWIN
  60         if (saved_euid != 0) {
  61                 privileged = 0;
  62                 return;
  63         }
  64 #endif
  65 #else
  66         if (geteuid() != 0) {
  67                 privileged = 0;
  68                 return;
  69         }
  70 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  71
  72         privileged = 1;
  73         temporarily_use_uid_effective = 1;
  74
  75         saved_egroupslen = getgroups(0, NULL);
  76         if (saved_egroupslen < 0)
  77                 fatal("getgroups: %.100s", strerror(errno));
  78         if (saved_egroupslen > 0) {
  79                 saved_egroups = xrealloc(saved_egroups,
  80                     saved_egroupslen * sizeof(gid_t));
  81                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  82                         fatal("getgroups: %.100s", strerror(errno));
  83         } else { /* saved_egroupslen == 0 */
  84                 if (saved_egroups != NULL)
  85                         xfree(saved_egroups);
  86         }
  87
  88         /* set and save the user's groups */
  89         if (user_groupslen == -1) {
  90                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
  91                         fatal("initgroups: %s: %.100s", pw->pw_name,
  92                             strerror(errno));
  93
  94                 user_groupslen = getgroups(0, NULL);
  95                 if (user_groupslen < 0)
  96                         fatal("getgroups: %.100s", strerror(errno));
  97                 if (user_groupslen > 0) {
  98                         user_groups = xrealloc(user_groups,
  99                             user_groupslen * sizeof(gid_t));
 100                         if (getgroups(user_groupslen, user_groups) < 0)
 101                                 fatal("getgroups: %.100s", strerror(errno));
 102                 } else { /* user_groupslen == 0 */
 103                         if (user_groups)
 104                                 xfree(user_groups);
 105                 }
 106         }
 107         /* Set the effective uid to the given (unprivileged) uid. */
 108         if (setgroups(user_groupslen, user_groups) < 0)
 109                 fatal("setgroups: %.100s", strerror(errno));
 110 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 111         /* Propagate the privileged gid to all of our gids. */
 112         if (setgid(getegid()) < 0)
 113                 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 114         /* Propagate the privileged uid to all of our uids. */
 115         if (setuid(geteuid()) < 0)
 116                 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 117 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 118         if (setegid(pw->pw_gid) < 0)
 119                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 120                     strerror(errno));
 121         if (seteuid(pw->pw_uid) == -1)
 122                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 123                     strerror(errno));
 124 }
 125
 126 /*
 127  * Restores to the original (privileged) uid.
 128  */
 129 void
 130 restore_uid(void)
 131 {
 132         /* it's a no-op unless privileged */
 133         if (!privileged) {
 134                 debug("restore_uid: (unprivileged)");
 135                 return;
 136         }
 137         if (!temporarily_use_uid_effective)
 138                 fatal("restore_uid: temporarily_use_uid not effective");
 139
 140 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 141         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 142         /* Set the effective uid back to the saved privileged uid. */
 143         if (seteuid(saved_euid) < 0)
 144                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 145         if (setegid(saved_egid) < 0)
 146                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 147 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 148         /*
 149          * We are unable to restore the real uid to its unprivileged value.
 150          * Propagate the real uid (usually more privileged) to effective uid
 151          * as well.
 152          */
 153         setuid(getuid());
 154         setgid(getgid());
 155 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 156
 157         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 158                 fatal("setgroups: %.100s", strerror(errno));
 159         temporarily_use_uid_effective = 0;
 160 }
 161
 162 /*
 163  * Permanently sets all uids to the given uid.  This cannot be
 164  * called while temporarily_use_uid is effective.
 165  */
 166 void
 167 permanently_set_uid(struct passwd *pw)
 168 {
 169         uid_t old_uid = getuid();
 170         gid_t old_gid = getgid();
 171
 172         if (temporarily_use_uid_effective)
 173                 fatal("permanently_set_uid: temporarily_use_uid effective");
 174         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 175             (u_int)pw->pw_gid);
 176
 177 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
 178         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 179                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 180 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
 181         if (setregid(pw->pw_gid, pw->pw_gid) < 0)
 182                 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 183 #else
 184         if (setegid(pw->pw_gid) < 0)
 185                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 186         if (setgid(pw->pw_gid) < 0)
 187                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 188 #endif
 189
 190 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 191         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 192                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 193 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 194         if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
 195                 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 196 #else
 197 # ifndef SETEUID_BREAKS_SETUID
 198         if (seteuid(pw->pw_uid) < 0)
 199                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 200 # endif
 201         if (setuid(pw->pw_uid) < 0)
 202                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 203 #endif
 204
 205 #ifndef HAVE_CYGWIN
 206         /* Try restoration of GID if changed (test clearing of saved gid) */
 207         if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 208             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 209                 fatal("%s: was able to restore old [e]gid", __func__);
 210 #endif
 211
 212         /* Verify GID drop was successful */
 213         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 214                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 215                     __func__, (u_int)getgid(), (u_int)getegid(),
 216                     (u_int)pw->pw_gid);
 217         }
 218
 219 #ifndef HAVE_CYGWIN
 220         /* Try restoration of UID if changed (test clearing of saved uid) */
 221         if (old_uid != pw->pw_uid &&
 222             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 223                 fatal("%s: was able to restore old [e]uid", __func__);
 224 #endif
 225
 226         /* Verify UID drop was successful */
 227         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 228                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 229                     __func__, (u_int)getuid(), (u_int)geteuid(),
 230                     (u_int)pw->pw_uid);
 231         }
 232 }