crypto/openssh-3.9p1/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         if (saved_euid != 0) {
  60                 privileged = 0;
  61                 return;
  62         }
  63 #else
  64         if (geteuid() != 0) {
  65                 privileged = 0;
  66                 return;
  67         }
  68 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
  69
  70         privileged = 1;
  71         temporarily_use_uid_effective = 1;
  72
  73         saved_egroupslen = getgroups(0, NULL);
  74         if (saved_egroupslen < 0)
  75                 fatal("getgroups: %.100s", strerror(errno));
  76         if (saved_egroupslen > 0) {
  77                 saved_egroups = xrealloc(saved_egroups,
  78                     saved_egroupslen * sizeof(gid_t));
  79                 if (getgroups(saved_egroupslen, saved_egroups) < 0)
  80                         fatal("getgroups: %.100s", strerror(errno));
  81         } else { /* saved_egroupslen == 0 */
  82                 if (saved_egroups != NULL)
  83                         xfree(saved_egroups);
  84         }
  85
  86         /* set and save the user's groups */
  87         if (user_groupslen == -1) {
  88                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
  89                         fatal("initgroups: %s: %.100s", pw->pw_name,
  90                             strerror(errno));
  91
  92                 user_groupslen = getgroups(0, NULL);
  93                 if (user_groupslen < 0)
  94                         fatal("getgroups: %.100s", strerror(errno));
  95                 if (user_groupslen > 0) {
  96                         user_groups = xrealloc(user_groups,
  97                             user_groupslen * sizeof(gid_t));
  98                         if (getgroups(user_groupslen, user_groups) < 0)
  99                                 fatal("getgroups: %.100s", strerror(errno));
 100                 } else { /* user_groupslen == 0 */
 101                         if (user_groups)
 102                                 xfree(user_groups);
 103                 }
 104         }
 105         /* Set the effective uid to the given (unprivileged) uid. */
 106         if (setgroups(user_groupslen, user_groups) < 0)
 107                 fatal("setgroups: %.100s", strerror(errno));
 108 #ifndef SAVED_IDS_WORK_WITH_SETEUID
 109         /* Propagate the privileged gid to all of our gids. */
 110         if (setgid(getegid()) < 0)
 111                 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
 112         /* Propagate the privileged uid to all of our uids. */
 113         if (setuid(geteuid()) < 0)
 114                 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
 115 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 116         if (setegid(pw->pw_gid) < 0)
 117                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
 118                     strerror(errno));
 119         if (seteuid(pw->pw_uid) == -1)
 120                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
 121                     strerror(errno));
 122 }
 123
 124 /*
 125  * Restores to the original (privileged) uid.
 126  */
 127 void
 128 restore_uid(void)
 129 {
 130         /* it's a no-op unless privileged */
 131         if (!privileged) {
 132                 debug("restore_uid: (unprivileged)");
 133                 return;
 134         }
 135         if (!temporarily_use_uid_effective)
 136                 fatal("restore_uid: temporarily_use_uid not effective");
 137
 138 #ifdef SAVED_IDS_WORK_WITH_SETEUID
 139         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 140         /* Set the effective uid back to the saved privileged uid. */
 141         if (seteuid(saved_euid) < 0)
 142                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 143         if (setegid(saved_egid) < 0)
 144                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 145 #else /* SAVED_IDS_WORK_WITH_SETEUID */
 146         /*
 147          * We are unable to restore the real uid to its unprivileged value.
 148          * Propagate the real uid (usually more privileged) to effective uid
 149          * as well.
 150          */
 151         setuid(getuid());
 152         setgid(getgid());
 153 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
 154
 155         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 156                 fatal("setgroups: %.100s", strerror(errno));
 157         temporarily_use_uid_effective = 0;
 158 }
 159
 160 /*
 161  * Permanently sets all uids to the given uid.  This cannot be
 162  * called while temporarily_use_uid is effective.
 163  */
 164 void
 165 permanently_set_uid(struct passwd *pw)
 166 {
 167         uid_t old_uid = getuid();
 168         gid_t old_gid = getgid();
 169
 170         if (temporarily_use_uid_effective)
 171                 fatal("permanently_set_uid: temporarily_use_uid effective");
 172         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 173             (u_int)pw->pw_gid);
 174
 175 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
 176         if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
 177                 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 178 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
 179         if (setregid(pw->pw_gid, pw->pw_gid) < 0)
 180                 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 181 #else
 182         if (setegid(pw->pw_gid) < 0)
 183                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 184         if (setgid(pw->pw_gid) < 0)
 185                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 186 #endif
 187
 188 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
 189         if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
 190                 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 191 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
 192         if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
 193                 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 194 #else
 195 # ifndef SETEUID_BREAKS_SETUID
 196         if (seteuid(pw->pw_uid) < 0)
 197                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 198 # endif
 199         if (setuid(pw->pw_uid) < 0)
 200                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 201 #endif
 202
 203         /* Try restoration of GID if changed (test clearing of saved gid) */
 204         if (old_gid != pw->pw_gid &&
 205             (setgid(old_gid) != -1 || setegid(old_gid) != -1))
 206                 fatal("%s: was able to restore old [e]gid", __func__);
 207
 208         /* Verify GID drop was successful */
 209         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 210                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 211                     __func__, (u_int)getgid(), (u_int)getegid(),
 212                     (u_int)pw->pw_gid);
 213         }
 214
 215 #ifndef HAVE_CYGWIN
 216         /* Try restoration of UID if changed (test clearing of saved uid) */
 217         if (old_uid != pw->pw_uid &&
 218             (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
 219                 fatal("%s: was able to restore old [e]uid", __func__);
 220 #endif
 221
 222         /* Verify UID drop was successful */
 223         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 224                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 225                     __func__, (u_int)getuid(), (u_int)geteuid(),
 226                     (u_int)pw->pw_uid);
 227         }
 228 }