sysdeps/unix/sysv/linux/faccessat.c

   1 /* Test for access to file, relative to open directory.  Linux version.
   2    Copyright (C) 2006-2014 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 <kernel-features.h>
  28 #include <sysdep.h>
  29
  30
  31 int
  32 faccessat (fd, file, mode, flag)
  33      int fd;
  34      const char *file;
  35      int mode;
  36      int flag;
  37 {
  38   if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
  39     {
  40       __set_errno (EINVAL);
  41       return -1;
  42     }
  43
  44 #ifdef __NR_faccessat
  45   if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure))
  46 # ifndef __ASSUME_ATFCTS
  47       && __have_atfcts >= 0
  48 # endif
  49       )
  50     {
  51       int result = INLINE_SYSCALL (faccessat, 3, fd, file, mode);
  52 # ifndef __ASSUME_ATFCTS
  53       if (result == -1 && errno == ENOSYS)
  54         __have_atfcts = -1;
  55       else
  56 # endif
  57         return result;
  58     }
  59 #endif
  60
  61 #ifndef __ASSUME_ATFCTS
  62   if ((!(flag & AT_EACCESS) || ! __libc_enable_secure)
  63 # ifndef __NR_laccess           /* Linux so far has no laccess syscall.  */
  64       && !(flag & AT_SYMLINK_NOFOLLOW)
  65 # endif
  66       )
  67     {
  68       /* If we are not set-uid or set-gid, access does the same.  */
  69       char *buf = NULL;
  70
  71       if (fd != AT_FDCWD && file[0] != '/')
  72         {
  73           size_t filelen = strlen (file);
  74           if (__builtin_expect (filelen == 0, 0))
  75             {
  76               __set_errno (ENOENT);
  77               return -1;
  78             }
  79
  80           static const char procfd[] = "/proc/self/fd/%d/%s";
  81           /* Buffer for the path name we are going to use.  It consists of
  82              - the string /proc/self/fd/
  83              - the file descriptor number
  84              - the file name provided.
  85              The final NUL is included in the sizeof.   A bit of overhead
  86              due to the format elements compensates for possible negative
  87              numbers.  */
  88           size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
  89           buf = alloca (buflen);
  90
  91           __snprintf (buf, buflen, procfd, fd, file);
  92           file = buf;
  93         }
  94
  95       int result;
  96       INTERNAL_SYSCALL_DECL (err);
  97
  98 # ifdef __NR_laccess
  99       if (flag & AT_SYMLINK_NOFOLLOW)
 100         result = INTERNAL_SYSCALL (laccess, err, 2, file, mode);
 101       else
 102 # endif
 103         result = INTERNAL_SYSCALL (access, err, 2, file, mode);
 104
 105       if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
 106         {
 107           __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, buf);
 108           result = -1;
 109         }
 110
 111       return result;
 112     }
 113 #endif
 114
 115   struct stat64 stats;
 116   if (__fxstatat64 (_STAT_VER, fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
 117     return -1;
 118
 119   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
 120 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
 121 # error Oops, portability assumptions incorrect.
 122 #endif
 123
 124   if (mode == F_OK)
 125     return 0;                   /* The file exists. */
 126
 127   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
 128
 129   /* The super-user can read and write any file, and execute any file
 130      that anyone can execute. */
 131   if (uid == 0 && ((mode & X_OK) == 0
 132                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 133     return 0;
 134
 135   int granted = (uid == stats.st_uid
 136                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
 137                  : (stats.st_gid == ((flag & AT_EACCESS)
 138                                      ? __getegid () : __getgid ())
 139                     || __group_member (stats.st_gid))
 140                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
 141                  : (stats.st_mode & mode));
 142
 143   if (granted == mode)
 144     return 0;
 145
 146   __set_errno (EACCES);
 147   return -1;
 148 }