sysdeps/unix/sysv/linux/faccessat.c

   1 /* Test for access to file, relative to open directory.  Linux version.
   2    Copyright (C) 2006-2015 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 (fd, file, mode, flag)
  32      int fd;
  33      const char *file;
  34      int mode;
  35      int flag;
  36 {
  37   if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
  38     {
  39       __set_errno (EINVAL);
  40       return -1;
  41     }
  42
  43   if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure)))
  44     return INLINE_SYSCALL (faccessat, 3, fd, file, mode);
  45
  46   struct stat64 stats;
  47   if (__fxstatat64 (_STAT_VER, fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
  48     return -1;
  49
  50   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
  51 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
  52 # error Oops, portability assumptions incorrect.
  53 #endif
  54
  55   if (mode == F_OK)
  56     return 0;                   /* The file exists. */
  57
  58   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
  59
  60   /* The super-user can read and write any file, and execute any file
  61      that anyone can execute. */
  62   if (uid == 0 && ((mode & X_OK) == 0
  63                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
  64     return 0;
  65
  66   int granted = (uid == stats.st_uid
  67                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
  68                  : (stats.st_gid == ((flag & AT_EACCESS)
  69                                      ? __getegid () : __getgid ())
  70                     || __group_member (stats.st_gid))
  71                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
  72                  : (stats.st_mode & mode));
  73
  74   if (granted == mode)
  75     return 0;
  76
  77   __set_errno (EACCES);
  78   return -1;
  79 }