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 <kernel-features.h>
  29 #include <sysdep.h>
  30
  31
  32 int
  33 faccessat (fd, file, mode, flag)
  34      int fd;
  35      const char *file;
  36      int mode;
  37      int flag;
  38 {
  39   if (flag & ~(AT_SYMLINK_NOFOLLOW | AT_EACCESS))
  40     {
  41       __set_errno (EINVAL);
  42       return -1;
  43     }
  44
  45 #ifdef __NR_faccessat
  46   if ((flag == 0 || ((flag & ~AT_EACCESS) == 0 && ! __libc_enable_secure))
  47 # ifndef __ASSUME_ATFCTS
  48       && __have_atfcts >= 0
  49 # endif
  50       )
  51     {
  52       int result = INLINE_SYSCALL (faccessat, 3, fd, file, mode);
  53 # ifndef __ASSUME_ATFCTS
  54       if (result == -1 && errno == ENOSYS)
  55         __have_atfcts = -1;
  56       else
  57 # endif
  58         return result;
  59     }
  60 #endif
  61
  62 #ifndef __ASSUME_ATFCTS
  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       char *buf = NULL;
  71
  72       if (fd != AT_FDCWD && file[0] != '/')
  73         {
  74           size_t filelen = strlen (file);
  75           static const char procfd[] = "/proc/self/fd/%d/%s";
  76           /* Buffer for the path name we are going to use.  It consists of
  77              - the string /proc/self/fd/
  78              - the file descriptor number
  79              - the file name provided.
  80              The final NUL is included in the sizeof.   A bit of overhead
  81              due to the format elements compensates for possible negative
  82              numbers.  */
  83           size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
  84           buf = alloca (buflen);
  85
  86           __snprintf (buf, buflen, procfd, fd, file);
  87           file = buf;
  88         }
  89
  90       int result;
  91       INTERNAL_SYSCALL_DECL (err);
  92
  93 # ifdef __NR_laccess
  94       if (flag & AT_SYMLINK_NOFOLLOW)
  95         result = INTERNAL_SYSCALL (laccess, err, 2, file, mode);
  96       else
  97 # endif
  98         result = INTERNAL_SYSCALL (access, err, 2, file, mode);
  99
 100       if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
 101         {
 102           __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, buf);
 103           result = -1;
 104         }
 105
 106       return result;
 107     }
 108 #endif
 109
 110   struct stat64 stats;
 111   if (fstatat64 (fd, file, &stats, flag & AT_SYMLINK_NOFOLLOW))
 112     return -1;
 113
 114   mode &= (X_OK | W_OK | R_OK); /* Clear any bogus bits. */
 115 #if R_OK != S_IROTH || W_OK != S_IWOTH || X_OK != S_IXOTH
 116 # error Oops, portability assumptions incorrect.
 117 #endif
 118
 119   if (mode == F_OK)
 120     return 0;                   /* The file exists. */
 121
 122   uid_t uid = (flag & AT_EACCESS) ? __geteuid () : __getuid ();
 123
 124   /* The super-user can read and write any file, and execute any file
 125      that anyone can execute. */
 126   if (uid == 0 && ((mode & X_OK) == 0
 127                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
 128     return 0;
 129
 130   int granted = (uid == stats.st_uid
 131                  ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
 132                  : (stats.st_gid == ((flag & AT_EACCESS)
 133                                      ? __getegid () : __getgid ())
 134                     || __group_member (stats.st_gid))
 135                  ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
 136                  : (stats.st_mode & mode));
 137
 138   if (granted == mode)
 139     return 0;
 140
 141   __set_errno (EACCES);
 142   return -1;
 143 }