sysdeps/unix/sysv/linux/faccessat.c

   1 /* Test for access to file, relative to open directory.  Linux version.
   2    Copyright (C) 2006-2017 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <sys/types.h>
  26 #include <alloca.h>
  27 #include <sysdep.h>
  28
  29
  30 int
  31 faccessat (int fd, const char *file, int mode, int flag)
  32 {
  33   if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
  34     return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
  35
  36   if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure)))
  37     return INLINE_SYSCALL (faccessat, 3, fd, file, mode);
  38
  39   struct stat64 stats;
  40   if (__fxstatat64 (_STAT_VER, fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
  41     return -1;
  42
  43   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
  44 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
  45 # error Oops, portability assumptions incorrect.
  46 #endif
  47
  48   if (mode == F_OK)
  49     return 0;                   /* The file exists. */
  50
  51   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
  52
  53   /* The super-user can read and write any file, and execute any file
  54      that anyone can execute. */
  55   if (uid == 0 && ((mode & X_OK) == 0
  56                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
  57     return 0;
  58
  59   int granted = (uid == stats.st_uid
  60                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
  61                  : (stats.st_gid == ((flag & AT_EACCESS)
  62                                      ? __getegid () : __getgid ())
  63                     || __group_member (stats.st_gid))
  64                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
  65                  : (stats.st_mode & mode));
  66
  67   if (granted == mode)
  68     return 0;
  69
  70   return INLINE_SYSCALL_ERROR_RETURN_VALUE (EACCES);
  71 }