lib/euidaccess.c

   1 /* euidaccess -- check if effective user id can access file
   2
   3    Copyright (C) 1990-1991, 1995, 1998, 2000, 2003-2006, 2008-2019 Free
   4    Software Foundation, Inc.
   5
   6    This file is part of the GNU C Library.
   7
   8    This program is free software: you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  20
  21 /* Written by David MacKenzie and Torbjorn Granlund.
  22    Adapted for GNU C library by Roland McGrath.  */
  23
  24 #ifndef _LIBC
  25 # include <config.h>
  26 #endif
  27
  28 #include <fcntl.h>
  29 #include <sys/types.h>
  30 #include <sys/stat.h>
  31 #include <unistd.h>
  32 #if defined _WIN32 && ! defined __CYGWIN__
  33 # include <io.h>
  34 #else
  35 # include "root-uid.h"
  36 #endif
  37
  38 #if HAVE_LIBGEN_H
  39 # include <libgen.h>
  40 #endif
  41
  42 #include <errno.h>
  43 #ifndef __set_errno
  44 # define __set_errno(val) errno = (val)
  45 #endif
  46
  47 #if defined EACCES && !defined EACCESS
  48 # define EACCESS EACCES
  49 #endif
  50
  51 #ifndef F_OK
  52 # define F_OK 0
  53 # define X_OK 1
  54 # define W_OK 2
  55 # define R_OK 4
  56 #endif
  57
  58
  59 #ifdef _LIBC
  60
  61 # define access __access
  62 # define getuid __getuid
  63 # define getgid __getgid
  64 # define geteuid __geteuid
  65 # define getegid __getegid
  66 # define group_member __group_member
  67 # define euidaccess __euidaccess
  68 # undef stat
  69 # define stat stat64
  70
  71 #endif
  72
  73 /* Return 0 if the user has permission of type MODE on FILE;
  74    otherwise, return -1 and set 'errno'.
  75    Like access, except that it uses the effective user and group
  76    id's instead of the real ones, and it does not always check for read-only
  77    file system, text busy, etc.  */
  78
  79 int
  80 euidaccess (const char *file, int mode)
  81 {
  82 #if HAVE_FACCESSAT                   /* glibc, AIX 7, Solaris 11, Cygwin 1.7 */
  83   return faccessat (AT_FDCWD, file, mode, AT_EACCESS);
  84 #elif defined EFF_ONLY_OK               /* IRIX, OSF/1, Interix */
  85   return access (file, mode | EFF_ONLY_OK);
  86 #elif defined ACC_SELF                  /* AIX */
  87   return accessx (file, mode, ACC_SELF);
  88 #elif HAVE_EACCESS                      /* FreeBSD */
  89   return eaccess (file, mode);
  90 #elif defined _WIN32 && ! defined __CYGWIN__  /* mingw */
  91   return _access (file, mode);
  92 #else              /* Mac OS X, NetBSD, OpenBSD, HP-UX, Solaris, Cygwin, BeOS */
  93
  94   uid_t uid = getuid ();
  95   gid_t gid = getgid ();
  96   uid_t euid = geteuid ();
  97   gid_t egid = getegid ();
  98   struct stat stats;
  99
 100 # if HAVE_DECL_SETREGID && PREFER_NONREENTRANT_EUIDACCESS
 101
 102   /* Define PREFER_NONREENTRANT_EUIDACCESS if you prefer euidaccess to
 103      return the correct result even if this would make it
 104      nonreentrant.  Define this only if your entire application is
 105      safe even if the uid or gid might temporarily change.  If your
 106      application uses signal handlers or threads it is probably not
 107      safe.  */
 108
 109   if (mode == F_OK)
 110     return stat (file, &stats);
 111   else
 112     {
 113       int result;
 114       int saved_errno;
 115
 116       if (uid != euid)
 117         setreuid (euid, uid);
 118       if (gid != egid)
 119         setregid (egid, gid);
 120
 121       result = access (file, mode);
 122       saved_errno = errno;
 123
 124       /* Restore them.  */
 125       if (uid != euid)
 126         setreuid (uid, euid);
 127       if (gid != egid)
 128         setregid (gid, egid);
 129
 130       errno = saved_errno;
 131       return result;
 132     }
 133
 134 # else
 135
 136   /* The following code assumes the traditional Unix model, and is not
 137      correct on systems that have ACLs or the like.  However, it's
 138      better than nothing, and it is reentrant.  */
 139
 140   unsigned int granted;
 141   if (uid == euid && gid == egid)
 142     /* If we are not set-uid or set-gid, access does the same.  */
 143     return access (file, mode);
 144
 145   if (stat (file, &stats) != 0)
 146     return -1;
 147
 148   /* The super-user can read and write any file, and execute any file
 149      that anyone can execute.  */
 150   if (euid == ROOT_UID
 151       && ((mode & X_OK) == 0
 152           || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 153     return 0;
 154
 155   /* Convert the mode to traditional form, clearing any bogus bits.  */
 156   if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
 157     mode &= 7;
 158   else
 159     mode = ((mode & R_OK ? 4 : 0)
 160             + (mode & W_OK ? 2 : 0)
 161             + (mode & X_OK ? 1 : 0));
 162
 163   if (mode == 0)
 164     return 0;                   /* The file exists.  */
 165
 166   /* Convert the file's permission bits to traditional form.  */
 167   if (S_IRUSR == (4 << 6) && S_IWUSR == (2 << 6) && S_IXUSR == (1 << 6)
 168       && S_IRGRP == (4 << 3) && S_IWGRP == (2 << 3) && S_IXGRP == (1 << 3)
 169       && S_IROTH == (4 << 0) && S_IWOTH == (2 << 0) && S_IXOTH == (1 << 0))
 170     granted = stats.st_mode;
 171   else
 172     granted = ((stats.st_mode & S_IRUSR ? 4 << 6 : 0)
 173                + (stats.st_mode & S_IWUSR ? 2 << 6 : 0)
 174                + (stats.st_mode & S_IXUSR ? 1 << 6 : 0)
 175                + (stats.st_mode & S_IRGRP ? 4 << 3 : 0)
 176                + (stats.st_mode & S_IWGRP ? 2 << 3 : 0)
 177                + (stats.st_mode & S_IXGRP ? 1 << 3 : 0)
 178                + (stats.st_mode & S_IROTH ? 4 << 0 : 0)
 179                + (stats.st_mode & S_IWOTH ? 2 << 0 : 0)
 180                + (stats.st_mode & S_IXOTH ? 1 << 0 : 0));
 181
 182   if (euid == stats.st_uid)
 183     granted >>= 6;
 184   else if (egid == stats.st_gid || group_member (stats.st_gid))
 185     granted >>= 3;
 186
 187   if ((mode & ~granted) == 0)
 188     return 0;
 189   __set_errno (EACCESS);
 190   return -1;
 191
 192 # endif
 193 #endif
 194 }
 195 #undef euidaccess
 196 #ifdef weak_alias
 197 weak_alias (__euidaccess, euidaccess)
 198 #endif
 199 \f
 200 #ifdef TEST
 201 # include <error.h>
 202 # include <stdio.h>
 203 # include <stdlib.h>
 204
 205 int
 206 main (int argc, char **argv)
 207 {
 208   char *file;
 209   int mode;
 210   int err;
 211
 212   if (argc < 3)
 213     abort ();
 214   file = argv[1];
 215   mode = atoi (argv[2]);
 216
 217   err = euidaccess (file, mode);
 218   printf ("%d\n", err);
 219   if (err != 0)
 220     error (0, errno, "%s", file);
 221   exit (0);
 222 }
 223 #endif