uidswap.c

   1 /* $OpenBSD: uidswap.c,v 1.30 2006/07/06 16:03:53 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 <pwd.h>
  20
  21 #include <grp.h>
  22
  23 #include "log.h"
  24 #include "uidswap.h"
  25 #include "xmalloc.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_WITH_SETEUID
  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 = NULL, *user_groups = NULL;
  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_WITH_SETEUID
  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 #ifndef HAVE_CYGWIN
  66         if (saved_euid != 0) {
  67                 privileged = 0;
  68                 return;
  69         }
  70 #endif
  71 #else
  72         if (geteuid() != 0) {
  73                 privileged = 0;
  74                 return;
  75         }
  76 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  77
  78         privileged = 1;
  79         temporarily_use_uid_effective = 1;
  80
  81         saved_egroupslen = getgroups(0, NULL);
  82         if (saved_egroupslen < 0)
  83                 fatal("getgroups: %.100s", strerror(errno));
  84         if (saved_egroupslen > 0) {
  85                 saved_egroups = xrealloc(saved_egroups,
  86                     saved_egroupslen, sizeof(gid_t));
  87                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  88                         fatal("getgroups: %.100s", strerror(errno));
  89         } else { /* saved_egroupslen == 0 */
  90                 if (saved_egroups != NULL)
  91                         xfree(saved_egroups);
  92         }
  93
  94         /* set and save the user's groups */
  95         if (user_groupslen == -1) {
  96                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
  97                         fatal("initgroups: %s: %.100s", pw->pw_name,
  98                             strerror(errno));
  99
 100                 user_groupslen = getgroups(0, NULL);
 101                 if (user_groupslen < 0)
 102                         fatal("getgroups: %.100s", strerror(errno));
 103                 if (user_groupslen > 0) {
 104                         user_groups = xrealloc(user_groups,
 105                             user_groupslen, sizeof(gid_t));
 106                         if (getgroups(user_groupslen, user_groups) < 0)
 107                                 fatal("getgroups: %.100s", strerror(errno));
 108                 } else { /* user_groupslen == 0 */
 109                         if (user_groups)
 110                                 xfree(user_groups);
 111                 }
 112         }
 113         /* Set the effective uid to the given (unprivileged) uid. */
 114         if (setgroups(user_groupslen, user_groups) < 0)
 115                 fatal("setgroups: %.100s", strerror(errno));
 116 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 117         /* Propagate the privileged gid to all of our gids. */
 118         if (setgid(getegid()) < 0)
 119                 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 120         /* Propagate the privileged uid to all of our uids. */
 121         if (setuid(geteuid()) < 0)
 122                 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 123 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 124         if (setegid(pw->pw_gid) < 0)
 125                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 126                     strerror(errno));
 127         if (seteuid(pw->pw_uid) == -1)
 128                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 129                     strerror(errno));
 130 }
 131
 132 void
 133 permanently_drop_suid(uid_t uid)
 134 {
 135         uid_t old_uid = getuid();
 136
 137         debug("permanently_drop_suid: %u", (u_int)uid);
 138 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 139         if (setresuid(uid, uid, uid) < 0)
 140                 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
 141 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 142         if (setreuid(uid, uid) < 0)
 143                 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
 144 #else
 145 # ifndef SETEUID_BREAKS_SETUID
 146         if (seteuid(uid) < 0)
 147                 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
 148 # endif
 149         if (setuid(uid) < 0)
 150                 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
 151 #endif
 152
 153 #ifndef HAVE_CYGWIN
 154         /* Try restoration of UID if changed (test clearing of saved uid) */
 155         if (old_uid != uid &&
 156             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 157                 fatal("%s: was able to restore old [e]uid", __func__);
 158 #endif
 159
 160         /* Verify UID drop was successful */
 161         if (getuid() != uid || geteuid() != uid) {
 162                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 163                     __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
 164         }
 165 }
 166
 167 /*
 168  * Restores to the original (privileged) uid.
 169  */
 170 void
 171 restore_uid(void)
 172 {
 173         /* it's a no-op unless privileged */
 174         if (!privileged) {
 175                 debug("restore_uid: (unprivileged)");
 176                 return;
 177         }
 178         if (!temporarily_use_uid_effective)
 179                 fatal("restore_uid: temporarily_use_uid not effective");
 180
 181 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 182         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 183         /* Set the effective uid back to the saved privileged uid. */
 184         if (seteuid(saved_euid) < 0)
 185                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 186         if (setegid(saved_egid) < 0)
 187                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 188 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 189         /*
 190          * We are unable to restore the real uid to its unprivileged value.
 191          * Propagate the real uid (usually more privileged) to effective uid
 192          * as well.
 193          */
 194         setuid(getuid());
 195         setgid(getgid());
 196 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 197
 198         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 199                 fatal("setgroups: %.100s", strerror(errno));
 200         temporarily_use_uid_effective = 0;
 201 }
 202
 203 /*
 204  * Permanently sets all uids to the given uid.  This cannot be
 205  * called while temporarily_use_uid is effective.
 206  */
 207 void
 208 permanently_set_uid(struct passwd *pw)
 209 {
 210         uid_t old_uid = getuid();
 211         gid_t old_gid = getgid();
 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 defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
 221         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 222                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 223 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
 224         if (setregid(pw->pw_gid, pw->pw_gid) < 0)
 225                 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 226 #else
 227         if (setegid(pw->pw_gid) < 0)
 228                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 229         if (setgid(pw->pw_gid) < 0)
 230                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 231 #endif
 232
 233 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 234         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 235                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 236 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 237         if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
 238                 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 239 #else
 240 # ifndef SETEUID_BREAKS_SETUID
 241         if (seteuid(pw->pw_uid) < 0)
 242                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 243 # endif
 244         if (setuid(pw->pw_uid) < 0)
 245                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 246 #endif
 247
 248 #ifndef HAVE_CYGWIN
 249         /* Try restoration of GID if changed (test clearing of saved gid) */
 250         if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
 251             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 252                 fatal("%s: was able to restore old [e]gid", __func__);
 253 #endif
 254
 255         /* Verify GID drop was successful */
 256         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 257                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 258                     __func__, (u_int)getgid(), (u_int)getegid(),
 259                     (u_int)pw->pw_gid);
 260         }
 261
 262 #ifndef HAVE_CYGWIN
 263         /* Try restoration of UID if changed (test clearing of saved uid) */
 264         if (old_uid != pw->pw_uid &&
 265             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 266                 fatal("%s: was able to restore old [e]uid", __func__);
 267 #endif
 268
 269         /* Verify UID drop was successful */
 270         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 271                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 272                     __func__, (u_int)getuid(), (u_int)geteuid(),
 273                     (u_int)pw->pw_uid);
 274         }
 275 }