gl/idpriv-droptemp.c

   1 /* Dropping uid/gid privileges of the current process temporarily.
   2    Copyright (C) 2009-2013 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 #include "idpriv.h"
  20
  21 #include <errno.h>
  22 #include <stdlib.h>
  23 #include <sys/types.h>
  24 #include <unistd.h>
  25
  26 /* The privileged uid and gid that the process had earlier.  */
  27 #if HAVE_GETUID
  28 static int saved_uid = -1;
  29 #endif
  30 #if HAVE_GETGID
  31 static int saved_gid = -1;
  32 #endif
  33
  34 int
  35 idpriv_temp_drop (void)
  36 {
  37 #if HAVE_GETEUID && HAVE_GETEGID && (HAVE_SETRESUID || HAVE_SETREUID) && (HAVE_SETRESGID || HAVE_SETREGID)
  38   int uid = getuid ();
  39   int gid = getgid ();
  40
  41   /* Find out about the privileged uid and gid at the first call.  */
  42   if (saved_uid == -1)
  43     saved_uid = geteuid ();
  44   if (saved_gid == -1)
  45     saved_gid = getegid ();
  46
  47   /* Drop the gid privilege first, because in some cases the gid privilege
  48      cannot be dropped after the uid privilege has been dropped.  */
  49
  50   /* This is for executables that have the setgid bit set.  */
  51 # if HAVE_SETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
  52   if (setresgid (-1, gid, saved_gid) < 0)
  53     return -1;
  54 # else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
  55   if (setregid (-1, gid) < 0)
  56     return -1;
  57 # endif
  58
  59   /* This is for executables that have the setuid bit set.  */
  60 # if HAVE_SETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
  61   /* See <http://www.usenix.org/events/sec02/full_papers/chen/chen.pdf>
  62      figure 14.  */
  63   if (setresuid (-1, uid, saved_uid) < 0)
  64     return -1;
  65 # else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
  66   if (setreuid (-1, uid) < 0)
  67     return -1;
  68 # endif
  69
  70   /* Verify that the privileges have really been dropped.
  71      This verification is here for security reasons.  Doesn't matter if it
  72      takes a couple of system calls.
  73      When the verification fails, it indicates that we need to use different
  74      API in the code above. Therefore 'abort ()', not 'return -1'.  */
  75 # if HAVE_GETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
  76   {
  77     uid_t real;
  78     uid_t effective;
  79     uid_t saved;
  80     if (getresuid (&real, &effective, &saved) < 0
  81         || real != uid
  82         || effective != uid
  83         || saved != saved_uid)
  84       abort ();
  85   }
  86 # else
  87 #  if HAVE_GETEUID
  88   if (geteuid () != uid)
  89     abort ();
  90 #  endif
  91   if (getuid () != uid)
  92     abort ();
  93 # endif
  94 # if HAVE_GETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
  95   {
  96     uid_t real;
  97     uid_t effective;
  98     uid_t saved;
  99     if (getresgid (&real, &effective, &saved) < 0
 100         || real != gid
 101         || effective != gid
 102         || saved != saved_gid)
 103       abort ();
 104   }
 105 # else
 106 #  if HAVE_GETEGID
 107   if (getegid () != gid)
 108     abort ();
 109 #  endif
 110   if (getgid () != gid)
 111     abort ();
 112 # endif
 113
 114   return 0;
 115 #else
 116   errno = ENOSYS;
 117   return -1;
 118 #endif
 119 }
 120
 121 int
 122 idpriv_temp_restore (void)
 123 {
 124 #if HAVE_GETEUID && HAVE_GETEGID && (HAVE_SETRESUID || HAVE_SETREUID) && (HAVE_SETRESGID || HAVE_SETREGID)
 125   int uid = getuid ();
 126   int gid = getgid ();
 127
 128   if (saved_uid == -1 || saved_gid == -1)
 129     /* Caller error: idpriv_temp_drop was never invoked.  */
 130     abort ();
 131
 132   /* Acquire the gid privilege last, because in some cases the gid privilege
 133      cannot be acquired before the uid privilege has been acquired.  */
 134
 135   /* This is for executables that have the setuid bit set.  */
 136 # if HAVE_SETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
 137   /* See <http://www.usenix.org/events/sec02/full_papers/chen/chen.pdf>
 138      figure 14.  */
 139   if (setresuid (-1, saved_uid, -1) < 0)
 140     return -1;
 141 # else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
 142   if (setreuid (-1, saved_uid) < 0)
 143     return -1;
 144 # endif
 145
 146   /* This is for executables that have the setgid bit set.  */
 147 # if HAVE_SETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
 148   if (setresgid (-1, saved_gid, -1) < 0)
 149     return -1;
 150 # else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
 151   if (setregid (-1, saved_gid) < 0)
 152     return -1;
 153 # endif
 154
 155   /* Verify that the privileges have really been acquired.
 156      This verification is here for security reasons.  Doesn't matter if it
 157      takes a couple of system calls.
 158      When the verification fails, it indicates that we need to use different
 159      API in the code above. Therefore 'abort ()', not 'return -1'.  */
 160 # if HAVE_GETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
 161   {
 162     uid_t real;
 163     uid_t effective;
 164     uid_t saved;
 165     if (getresuid (&real, &effective, &saved) < 0
 166         || real != uid
 167         || effective != saved_uid
 168         || saved != saved_uid)
 169       abort ();
 170   }
 171 # else
 172 #  if HAVE_GETEUID
 173   if (geteuid () != saved_uid)
 174     abort ();
 175 #  endif
 176   if (getuid () != uid)
 177     abort ();
 178 # endif
 179 # if HAVE_GETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
 180   {
 181     uid_t real;
 182     uid_t effective;
 183     uid_t saved;
 184     if (getresgid (&real, &effective, &saved) < 0
 185         || real != gid
 186         || effective != saved_gid
 187         || saved != saved_gid)
 188       abort ();
 189   }
 190 # else
 191 #  if HAVE_GETEGID
 192   if (getegid () != saved_gid)
 193     abort ();
 194 #  endif
 195   if (getgid () != gid)
 196     abort ();
 197 # endif
 198
 199   return 0;
 200 #else
 201   errno = ENOSYS;
 202   return -1;
 203 #endif
 204 }