crypto/openssh/uidswap.c

   1 /* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker 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 <errno.h>
  18 #include <pwd.h>
  19 #include <string.h>
  20 #include <unistd.h>
  21 #include <limits.h>
  22 #include <stdarg.h>
  23 #include <stdlib.h>
  24
  25 #include <grp.h>
  26
  27 #include "log.h"
  28 #include "uidswap.h"
  29 #include "xmalloc.h"
  30
  31 /*
  32  * Note: all these functions must work in all of the following cases:
  33  *    1. euid=0, ruid=0
  34  *    2. euid=0, ruid!=0
  35  *    3. euid!=0, ruid!=0
  36  * Additionally, they must work regardless of whether the system has
  37  * POSIX saved uids or not.
  38  */
  39
  40 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
  41 /* Lets assume that posix saved ids also work with seteuid, even though that
  42    is not part of the posix specification. */
  43 #define SAVED_IDS_WORK_WITH_SETEUID
  44 /* Saved effective uid. */
  45 static uid_t    saved_euid = 0;
  46 static gid_t    saved_egid = 0;
  47 #endif
  48
  49 /* Saved effective uid. */
  50 static int      privileged = 0;
  51 static int      temporarily_use_uid_effective = 0;
  52 static gid_t    *saved_egroups = NULL, *user_groups = NULL;
  53 static int      saved_egroupslen = -1, user_groupslen = -1;
  54
  55 /*
  56  * Temporarily changes to the given uid.  If the effective user
  57  * id is not root, this does nothing.  This call cannot be nested.
  58  */
  59 void
  60 temporarily_use_uid(struct passwd *pw)
  61 {
  62         /* Save the current euid, and egroups. */
  63 #ifdef SAVED_IDS_WORK_WITH_SETEUID
  64         saved_euid = geteuid();
  65         saved_egid = getegid();
  66         debug("temporarily_use_uid: %u/%u (e=%u/%u)",
  67             (u_int)pw->pw_uid, (u_int)pw->pw_gid,
  68             (u_int)saved_euid, (u_int)saved_egid);
  69 #ifndef HAVE_CYGWIN
  70         if (saved_euid != 0) {
  71                 privileged = 0;
  72                 return;
  73         }
  74 #endif
  75 #else
  76         if (geteuid() != 0) {
  77                 privileged = 0;
  78                 return;
  79         }
  80 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  81
  82         privileged = 1;
  83         temporarily_use_uid_effective = 1;
  84
  85         saved_egroupslen = getgroups(0, NULL);
  86         if (saved_egroupslen < 0)
  87                 fatal("getgroups: %.100s", strerror(errno));
  88         if (saved_egroupslen > 0) {
  89                 saved_egroups = xreallocarray(saved_egroups,
  90                     saved_egroupslen, sizeof(gid_t));
  91                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  92                         fatal("getgroups: %.100s", strerror(errno));
  93         } else { /* saved_egroupslen == 0 */
  94                 free(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 = xreallocarray(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                         free(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 #ifndef NO_UID_RESTORATION_TEST
 138         uid_t old_uid = getuid();
 139 #endif
 140
 141         debug("permanently_drop_suid: %u", (u_int)uid);
 142         if (setresuid(uid, uid, uid) < 0)
 143                 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
 144
 145 #ifndef NO_UID_RESTORATION_TEST
 146         /*
 147          * Try restoration of UID if changed (test clearing of saved uid).
 148          *
 149          * Note that we don't do this on Cygwin, or on Solaris-based platforms
 150          * where fine-grained privileges are available (the user might be
 151          * deliberately allowed the right to setuid back to root).
 152          */
 153         if (old_uid != uid &&
 154             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 155                 fatal("%s: was able to restore old [e]uid", __func__);
 156 #endif
 157
 158         /* Verify UID drop was successful */
 159         if (getuid() != uid || geteuid() != uid) {
 160                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 161                     __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
 162         }
 163 }
 164
 165 /*
 166  * Restores to the original (privileged) uid.
 167  */
 168 void
 169 restore_uid(void)
 170 {
 171         /* it's a no-op unless privileged */
 172         if (!privileged) {
 173                 debug("restore_uid: (unprivileged)");
 174                 return;
 175         }
 176         if (!temporarily_use_uid_effective)
 177                 fatal("restore_uid: temporarily_use_uid not effective");
 178
 179 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 180         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 181         /* Set the effective uid back to the saved privileged uid. */
 182         if (seteuid(saved_euid) < 0)
 183                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 184         if (setegid(saved_egid) < 0)
 185                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 186 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 187         /*
 188          * We are unable to restore the real uid to its unprivileged value.
 189          * Propagate the real uid (usually more privileged) to effective uid
 190          * as well.
 191          */
 192         setuid(getuid());
 193         setgid(getgid());
 194 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 195
 196         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 197                 fatal("setgroups: %.100s", strerror(errno));
 198         temporarily_use_uid_effective = 0;
 199 }
 200
 201 /*
 202  * Permanently sets all uids to the given uid.  This cannot be
 203  * called while temporarily_use_uid is effective.
 204  */
 205 void
 206 permanently_set_uid(struct passwd *pw)
 207 {
 208 #ifndef NO_UID_RESTORATION_TEST
 209         uid_t old_uid = getuid();
 210         gid_t old_gid = getgid();
 211 #endif
 212
 213         if (pw == NULL)
 214                 fatal("permanently_set_uid: no user given");
 215         if (temporarily_use_uid_effective)
 216                 fatal("permanently_set_uid: temporarily_use_uid effective");
 217         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 218             (u_int)pw->pw_gid);
 219
 220         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 221                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 222
 223 #ifdef __APPLE__
 224         /*
 225          * OS X requires initgroups after setgid to opt back into
 226          * memberd support for >16 supplemental groups.
 227          */
 228         if (initgroups(pw->pw_name, pw->pw_gid) < 0)
 229                 fatal("initgroups %.100s %u: %.100s",
 230                     pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
 231 #endif
 232
 233         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 234                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 235
 236 #ifndef NO_UID_RESTORATION_TEST
 237         /* Try restoration of GID if changed (test clearing of saved gid) */
 238         if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 239             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 240                 fatal("%s: was able to restore old [e]gid", __func__);
 241 #endif
 242
 243         /* Verify GID drop was successful */
 244         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 245                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 246                     __func__, (u_int)getgid(), (u_int)getegid(),
 247                     (u_int)pw->pw_gid);
 248         }
 249
 250 #ifndef NO_UID_RESTORATION_TEST
 251         /* Try restoration of UID if changed (test clearing of saved uid) */
 252         if (old_uid != pw->pw_uid &&
 253             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 254                 fatal("%s: was able to restore old [e]uid", __func__);
 255 #endif
 256
 257         /* Verify UID drop was successful */
 258         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 259                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 260                     __func__, (u_int)getuid(), (u_int)geteuid(),
 261                     (u_int)pw->pw_uid);
 262         }
 263 }