sysdeps/unix/sysv/linux/fchmodat.c

   1 /* Change the protections of 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 fchmodat (fd, file, mode, flag)
  32      int fd;
  33      const char *file;
  34      mode_t mode;
  35      int flag;
  36 {
  37   if (flag & ~AT_SYMLINK_NOFOLLOW)
  38     {
  39       __set_errno (EINVAL);
  40       return -1;
  41     }
  42 #ifndef __NR_lchmod             /* Linux so far has no lchmod syscall.  */
  43   if (flag & AT_SYMLINK_NOFOLLOW)
  44     {
  45       __set_errno (ENOTSUP);
  46       return -1;
  47     }
  48 #endif
  49
  50   char *buf = NULL;
  51
  52   if (fd != AT_FDCWD && file[0] != '/')
  53     {
  54       size_t filelen = strlen (file);
  55       static const char procfd[] = "/proc/self/fd/%d/%s";
  56       /* Buffer for the path name we are going to use.  It consists of
  57          - the string /proc/self/fd/
  58          - the file descriptor number
  59          - the file name provided.
  60          The final NUL is included in the sizeof.   A bit of overhead
  61          due to the format elements compensates for possible negative
  62          numbers.  */
  63       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
  64       buf = alloca (buflen);
  65
  66       __snprintf (buf, buflen, procfd, fd, file);
  67       file = buf;
  68     }
  69
  70   int result;
  71   INTERNAL_SYSCALL_DECL (err);
  72
  73 #ifdef __NR_lchmod
  74   if (flag & AT_SYMLINK_NOFOLLOW)
  75     result = INTERNAL_SYSCALL (lchmod, err, 2, file, mode);
  76   else
  77 #endif
  78     result = INTERNAL_SYSCALL (chmod, err, 2, file, mode);
  79
  80   if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
  81     {
  82       __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, buf);
  83       result = -1;
  84     }
  85
  86   return result;
  87 }