kc3-lang/gnulib/lib/chdir-safer.c

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• Hash : ff0b56d9
  Author :
  Date : 2008-05-10T15:19:43
  

  Make chdir-safer.c more efficient on a system with no symlinks.
  
  * lib/chdir-safer.c (chdir_no_follow): Skip lstat and fstat calls
  also if ELOOP is zero.  Suggested by Bruno Haible.
  

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• lib/chdir-safer.c

• /* much like chdir(2), but safer
  
     Copyright (C) 2005-2006, 2008 Free Software Foundation, Inc.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 3 of the License, or
     (at your option) any later version.
  
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  
  /* written by Jim Meyering */
  
  #include <config.h>
  
  #include "chdir-safer.h"
  
  #include <stdbool.h>
  #include <fcntl.h>
  #include <errno.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include "same-inode.h"
  
  #ifndef ELOOP
  # define ELOOP 0
  #endif
  
  /* Like chdir, but fail if DIR is a symbolic link to a directory (or
     similar funny business), or if DIR is not readable.  This avoids a
     minor race condition between when a directory is created or statted
     and when the process chdirs into it.  */
  int
  chdir_no_follow (char const *dir)
  {
    int result = 0;
    int saved_errno;
    int fd = open (dir,
  		 O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK);
    if (fd < 0)
      return -1;
  
    /* If open follows symlinks, lstat DIR and fstat FD to ensure that
       they are the same file; if they are different files, set errno to
       ELOOP (the same value that open uses for symlinks with
       O_NOFOLLOW) so the caller can report a failure.
       Skip this check if ELOOP == 0, which should be the case
       on any system that lacks symlink support.  */
    if (ELOOP && ! HAVE_WORKING_O_NOFOLLOW)
      {
        struct stat sb1;
        result = lstat (dir, &sb1);
        if (result == 0)
  	{
  	  struct stat sb2;
  	  result = fstat (fd, &sb2);
  	  if (result == 0 && ! SAME_INODE (sb1, sb2))
  	    {
  	      errno = ELOOP;
  	      result = -1;
  	    }
  	}
      }
  
    if (result == 0)
      result = fchdir (fd);
  
    saved_errno = errno;
    close (fd);
    errno = saved_errno;
    return result;
  }
  

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