1  /* Test for access to file, relative to open directory.  Linux version.
       2     Copyright (C) 2006-2023 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  #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)