sysdeps/posix/euidaccess.c

   1 /* Check if effective user id can access file
   2    Copyright (C) 1990-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 /* Written by David MacKenzie and Torbjorn Granlund.
  20    Adapted for GNU C library by Roland McGrath.  */
  21
  22 #ifdef HAVE_CONFIG_H
  23 # include <config.h>
  24 #endif
  25
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28
  29 #ifdef S_IEXEC
  30 # ifndef S_IXUSR
  31 #  define S_IXUSR S_IEXEC
  32 # endif
  33 # ifndef S_IXGRP
  34 #  define S_IXGRP (S_IEXEC >> 3)
  35 # endif
  36 # ifndef S_IXOTH
  37 #  define S_IXOTH (S_IEXEC >> 6)
  38 # endif
  39 #endif /* S_IEXEC */
  40
  41 #if defined HAVE_UNISTD_H || defined _LIBC
  42 # include <unistd.h>
  43 #endif
  44
  45 #ifndef _POSIX_VERSION
  46 uid_t getuid ();
  47 gid_t getgid ();
  48 uid_t geteuid ();
  49 gid_t getegid ();
  50 #endif /* not POSIX_VERSION */
  51
  52 #include <errno.h>
  53 #ifndef errno
  54 extern int errno;
  55 #endif
  56 #ifndef __set_errno
  57 # define __set_errno(val) errno = (val)
  58 #endif
  59
  60 #if defined EACCES && !defined EACCESS
  61 # define EACCESS EACCES
  62 #endif
  63
  64 #ifndef F_OK
  65 # define F_OK 0
  66 # define X_OK 1
  67 # define W_OK 2
  68 # define R_OK 4
  69 #endif
  70
  71 #if !defined S_IROTH && defined R_OK
  72 # define S_IROTH R_OK
  73 #endif
  74 #if !defined S_IWOTH && defined W_OK
  75 # define S_IWOTH W_OK
  76 #endif
  77 #if !defined S_IXOTH && defined X_OK
  78 # define S_IXOTH X_OK
  79 #endif
  80
  81
  82 #ifdef _LIBC
  83
  84 # define group_member __group_member
  85 # define euidaccess __euidaccess
  86
  87 #else
  88
  89 /* The user's real user id. */
  90 static uid_t uid;
  91
  92 /* The user's real group id. */
  93 static gid_t gid;
  94
  95 /* The user's effective user id. */
  96 static uid_t euid;
  97
  98 /* The user's effective group id. */
  99 static gid_t egid;
 100
 101 /* Nonzero if UID, GID, EUID, and EGID have valid values. */
 102 static int have_ids;
 103
 104 # ifdef HAVE_GETGROUPS
 105 int group_member ();
 106 # else
 107 #  define group_member(gid)     0
 108 # endif
 109
 110 #endif
 111
 112
 113 /* Return 0 if the user has permission of type MODE on file PATH;
 114    otherwise, return -1 and set `errno' to EACCESS.
 115    Like access, except that it uses the effective user and group
 116    id's instead of the real ones, and it does not check for read-only
 117    filesystem, text busy, etc. */
 118
 119 int
 120 euidaccess (const char *path, int mode)
 121 {
 122   struct __stat64_t64 stats;
 123   int granted;
 124
 125 #ifdef  _LIBC
 126   uid_t euid;
 127   gid_t egid;
 128 #else
 129   if (have_ids == 0)
 130     {
 131       have_ids = 1;
 132       uid = getuid ();
 133       gid = getgid ();
 134       euid = geteuid ();
 135       egid = getegid ();
 136     }
 137
 138   if (uid == euid && gid == egid)
 139     /* If we are not set-uid or set-gid, access does the same.  */
 140     return access (path, mode);
 141 #endif
 142
 143   if (__stat64_time64 (path, &stats))
 144     return -1;
 145
 146   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
 147 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
 148   ?error Oops, portability assumptions incorrect.
 149 #endif
 150
 151   if (mode == F_OK)
 152     return 0;                   /* The file exists. */
 153
 154 #ifdef  _LIBC
 155   /* Now we need the IDs.  */
 156   euid = __geteuid ();
 157   egid = __getegid ();
 158
 159   if (__getuid () == euid && __getgid () == egid)
 160     /* If we are not set-uid or set-gid, access does the same.  */
 161     return __access (path, mode);
 162 #endif
 163
 164   /* The super-user can read and write any file, and execute any file
 165      that anyone can execute. */
 166   if (euid == 0 && ((mode & X_OK) == 0
 167                     || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 168     return 0;
 169
 170   if (euid == stats.st_uid)
 171     granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
 172   else if (egid == stats.st_gid || group_member (stats.st_gid))
 173     granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
 174   else
 175     granted = (stats.st_mode & mode);
 176   /* XXX Add support for ACLs.  */
 177   if (granted == mode)
 178     return 0;
 179   __set_errno (EACCESS);
 180   return -1;
 181 }
 182 #undef euidaccess
 183 #undef eaccess
 184 #ifdef weak_alias
 185 weak_alias (__euidaccess, euidaccess)
 186 weak_alias (__euidaccess, eaccess)
 187 #endif
 188 \f
 189 #ifdef TEST
 190 # include <stdio.h>
 191 # include <errno.h>
 192 # include "error.h"
 193
 194 char *program_name;
 195
 196 int
 197 main (int argc, char **argv)
 198 {
 199   char *file;
 200   int mode;
 201   int err;
 202
 203   program_name = argv[0];
 204   if (argc < 3)
 205     abort ();
 206   file = argv[1];
 207   mode = atoi (argv[2]);
 208
 209   err = euidaccess (file, mode);
 210   printf ("%d\n", err);
 211   if (err != 0)
 212     error (0, errno, "%s", file);
 213   exit (0);
 214 }
 215 #endif