crypto/external/bsd/openssh/dist/uidswap.c

   1 /*      $NetBSD$        */
   2 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */
   3 /*
   4  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   5  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   6  *                    All rights reserved
   7  * Code for uid-swapping.
   8  *
   9  * As far as I am concerned, the code I have written for this software
  10  * can be used freely for any purpose.  Any derived versions of this
  11  * software must be clearly marked as such, and if the derived work is
  12  * incompatible with the protocol description in the RFC file, it must be
  13  * called by a name other than "ssh" or "Secure Shell".
  14  */
  15
  16 #include "includes.h"
  17 __RCSID("$NetBSD: uidswap.c,v 1.4 2006/09/28 21:22:15 christos Exp $");
  18 #include <sys/param.h>
  19 #include <errno.h>
  20 #include <pwd.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <stdarg.h>
  24
  25 #include "log.h"
  26 #include "uidswap.h"
  27
  28 /*
  29  * Note: all these functions must work in all of the following cases:
  30  *    1. euid=0, ruid=0
  31  *    2. euid=0, ruid!=0
  32  *    3. euid!=0, ruid!=0
  33  * Additionally, they must work regardless of whether the system has
  34  * POSIX saved uids or not.
  35  */
  36
  37 /* Lets assume that posix saved ids also work with seteuid, even though that
  38    is not part of the posix specification. */
  39
  40 /* Saved effective uid. */
  41 static int      privileged = 0;
  42 static int      temporarily_use_uid_effective = 0;
  43 static uid_t    saved_euid = 0;
  44 static gid_t    saved_egid;
  45 static gid_t    saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX];
  46 static int      saved_egroupslen = -1, user_groupslen = -1;
  47
  48 /*
  49  * Temporarily changes to the given uid.  If the effective user
  50  * id is not root, this does nothing.  This call cannot be nested.
  51  */
  52 void
  53 temporarily_use_uid(struct passwd *pw)
  54 {
  55         /* Save the current euid, and egroups. */
  56         saved_euid = geteuid();
  57         saved_egid = getegid();
  58         debug("temporarily_use_uid: %u/%u (e=%u/%u)",
  59             (u_int)pw->pw_uid, (u_int)pw->pw_gid,
  60             (u_int)saved_euid, (u_int)saved_egid);
  61         if (saved_euid != 0) {
  62                 privileged = 0;
  63                 return;
  64         }
  65         privileged = 1;
  66         temporarily_use_uid_effective = 1;
  67         saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups);
  68         if (saved_egroupslen < 0)
  69                 fatal("getgroups: %.100s", strerror(errno));
  70
  71         /* set and save the user's groups */
  72         if (user_groupslen == -1) {
  73                 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
  74                         fatal("initgroups: %s: %.100s", pw->pw_name,
  75                             strerror(errno));
  76                 user_groupslen = getgroups(NGROUPS_MAX, user_groups);
  77                 if (user_groupslen < 0)
  78                         fatal("getgroups: %.100s", strerror(errno));
  79         }
  80         /* Set the effective uid to the given (unprivileged) uid. */
  81         if (setgroups(user_groupslen, user_groups) < 0)
  82                 fatal("setgroups: %.100s", strerror(errno));
  83         if (setegid(pw->pw_gid) < 0)
  84                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
  85                     strerror(errno));
  86         if (seteuid(pw->pw_uid) == -1)
  87                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
  88                     strerror(errno));
  89 }
  90
  91 /*
  92  * Restores to the original (privileged) uid.
  93  */
  94 void
  95 restore_uid(void)
  96 {
  97         /* it's a no-op unless privileged */
  98         if (!privileged) {
  99                 debug("restore_uid: (unprivileged)");
 100                 return;
 101         }
 102         if (!temporarily_use_uid_effective)
 103                 fatal("restore_uid: temporarily_use_uid not effective");
 104         debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
 105         /* Set the effective uid back to the saved privileged uid. */
 106         if (seteuid(saved_euid) < 0)
 107                 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
 108         if (setgroups(saved_egroupslen, saved_egroups) < 0)
 109                 fatal("setgroups: %.100s", strerror(errno));
 110         if (setegid(saved_egid) < 0)
 111                 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
 112         temporarily_use_uid_effective = 0;
 113 }
 114
 115 /*
 116  * Permanently sets all uids to the given uid.  This cannot be
 117  * called while temporarily_use_uid is effective.
 118  */
 119 void
 120 permanently_set_uid(struct passwd *pw)
 121 {
 122         if (pw == NULL)
 123                 fatal("permanently_set_uid: no user given");
 124         if (temporarily_use_uid_effective)
 125                 fatal("permanently_set_uid: temporarily_use_uid effective");
 126         debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
 127             (u_int)pw->pw_gid);
 128
 129         if (setgid(pw->pw_gid) < 0)
 130                 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 131         if (setegid(pw->pw_gid) < 0)
 132                 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
 133
 134         if (setuid(pw->pw_uid) < 0)
 135                 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 136         if (seteuid(pw->pw_uid) < 0)
 137                 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
 138
 139         /* Verify GID drop was successful */
 140         if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
 141                 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
 142                     __func__, (u_int)getgid(), (u_int)getegid(),
 143                     (u_int)pw->pw_gid);
 144         }
 145
 146         /* Verify UID drop was successful */
 147         if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
 148                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 149                     __func__, (u_int)getuid(), (u_int)geteuid(),
 150                     (u_int)pw->pw_uid);
 151         }
 152 }
 153
 154 void
 155 permanently_drop_suid(uid_t uid)
 156 {
 157         debug("permanently_drop_suid: %u", (u_int)uid);
 158         if (seteuid(uid) < 0)
 159                 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
 160         if (setuid(uid) < 0)
 161                 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
 162
 163         /* Verify UID drop was successful */
 164         if (getuid() != uid || geteuid() != uid) {
 165                 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
 166                     __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
 167         }
 168 }