sysdeps/unix/sysv/linux/faccessat.c

   1 /* Test for access to file, relative to open directory.  Linux version.
   2    Copyright (C) 2006-2024 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 #include <fcntl.h>
  20 #include <unistd.h>
  21 #include <sys/types.h>
  22 #include <sys/stat.h>
  23 #include <sysdep.h>
  24
  25
  26 int
  27 __faccessat (int fd, const char *file, int mode, int flag)
  28 {
  29   int ret = INLINE_SYSCALL_CALL (faccessat2, fd, file, mode, flag);
  30 #if __ASSUME_FACCESSAT2
  31   return ret;
  32 #else
  33   if (ret == 0 || errno != ENOSYS)
  34     return ret;
  35
  36   if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
  37     return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
  38
  39   if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure)))
  40     return INLINE_SYSCALL (faccessat, 3, fd, file, mode);
  41
  42   struct __stat64_t64 stats;
  43   if (__fstatat64_time64 (fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
  44     return -1;
  45
  46   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
  47 # if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
  48 #  error Oops, portability assumptions incorrect.
  49 # endif
  50
  51   if (mode == F_OK)
  52     return 0;                   /* The file exists. */
  53
  54   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
  55
  56   /* The super-user can read and write any file, and execute any file
  57      that anyone can execute. */
  58   if (uid == 0 && ((mode & X_OK) == 0
  59                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
  60     return 0;
  61
  62   int granted = (uid == stats.st_uid
  63                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
  64                  : (stats.st_gid == ((flag & AT_EACCESS)
  65                                      ? __getegid () : __getgid ())
  66                     || __group_member (stats.st_gid))
  67                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
  68                  : (stats.st_mode & mode));
  69
  70   if (granted == mode)
  71     return 0;
  72
  73   return INLINE_SYSCALL_ERROR_RETURN_VALUE (EACCES);
  74 #endif /* !__ASSUME_FACCESSAT2 */
  75 }
  76 weak_alias (__faccessat, faccessat)