sysdeps/unix/sysv/linux/faccessat.c

   1 /* Test for access to file, relative to open directory.  Linux version.
   2    Copyright (C) 2006 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <stddef.h>
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <sys/types.h>
  27 #include <alloca.h>
  28 #include <sysdep.h>
  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   char *buf = NULL;
  44
  45   if (fd != AT_FDCWD && file[0] != '/')
  46     {
  47       size_t filelen = strlen (file);
  48       static const char procfd[] = "/proc/self/fd/%d/%s";
  49       /* Buffer for the path name we are going to use.  It consists of
  50          - the string /proc/self/fd/
  51          - the file descriptor number
  52          - the file name provided.
  53          The final NUL is included in the sizeof.   A bit of overhead
  54          due to the format elements compensates for possible negative
  55          numbers.  */
  56       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
  57       buf = alloca (buflen);
  58
  59       __snprintf (buf, buflen, procfd, fd, file);
  60       file = buf;
  61     }
  62
  63   if ((!(flag & AT_EACCESS) || ! __libc_enable_secure)
  64 #ifndef __NR_laccess            /* Linux so far has no laccess syscall.  */
  65       && !(flag & AT_SYMLINK_NOFOLLOW)
  66 #endif
  67       )
  68     {
  69       /* If we are not set-uid or set-gid, access does the same.  */
  70
  71       int result;
  72       INTERNAL_SYSCALL_DECL (err);
  73
  74 #ifdef __NR_laccess
  75       if (flag & AT_SYMLINK_NOFOLLOW)
  76         result = INTERNAL_SYSCALL (laccess, err, 2, file, mode);
  77       else
  78 #endif
  79         result = INTERNAL_SYSCALL (access, err, 2, file, mode);
  80
  81       if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
  82         {
  83           __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, buf);
  84           result = -1;
  85         }
  86
  87       return result;
  88     }
  89
  90   struct stat64 stats;
  91   if (fstatat64 (fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
  92     return -1;
  93
  94   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
  95 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
  96 # error Oops, portability assumptions incorrect.
  97 #endif
  98
  99   if (mode == F_OK)
 100     return 0;                   /* The file exists. */
 101
 102   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
 103
 104   /* The super-user can read and write any file, and execute any file
 105      that anyone can execute. */
 106   if (uid == 0 && ((mode & X_OK) == 0
 107                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 108     return 0;
 109
 110   int granted = (uid == stats.st_uid
 111                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
 112                  : (stats.st_gid == ((flag & AT_EACCESS)
 113                                      ? __getegid () : __getgid ())
 114                     || __group_member (stats.st_gid))
 115                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
 116                  : (stats.st_mode & mode));
 117
 118   if (granted == mode)
 119     return 0;
 120
 121   __set_errno (EACCES);
 122   return -1;
 123 }