lib/getcwd.c

   1 /* Provide a replacement for the POSIX getcwd function.
   2    Copyright (C) 2003 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #include <config.h>
  21
  22 #include <stdlib.h>
  23 #include <string.h>
  24
  25 #include <errno.h>
  26 #ifndef errno
  27 extern int errno;
  28 #endif
  29
  30 #include <sys/types.h>
  31
  32 #include "pathmax.h"
  33 #include "same.h"
  34
  35 /* Guess high, because that makes the test below more conservative.
  36    But this is a kludge, because we should really use
  37    pathconf (".", _PC_NAME_MAX).  But it's probably not worth the cost.  */
  38 #define KLUDGE_POSIX_NAME_MAX 255
  39
  40 #define MAX_SAFE_LEN (PATH_MAX - 1 - KLUDGE_POSIX_NAME_MAX - 1)
  41
  42 /* Undefine getcwd here, as near the use as possible, in case any
  43    of the files included above define it to rpl_getcwd.  */
  44 #undef getcwd
  45
  46 /* Any declaration of getcwd from headers included above has
  47    been changed to a declaration of rpl_getcwd.  Declare it here.  */
  48 extern char *getcwd (char *buf, size_t size);
  49
  50 /* This is a wrapper for getcwd.
  51    Some implementations (at least GNU libc 2.3.1 + linux-2.4.20) return
  52    non-NULL for a working directory name longer than PATH_MAX, yet the
  53    returned string is a strict prefix of the desired directory name.
  54    Upon such a failure, free the offending string, set errno to
  55    ENAMETOOLONG, and return NULL.
  56
  57    I've heard that this is a Linux kernel bug, and that it has
  58    been fixed between 2.4.21-pre3 and 2.4.21-pre4.  */
  59
  60 char *
  61 rpl_getcwd (char *buf, size_t size)
  62 {
  63   char *cwd = getcwd (buf, size);
  64
  65   if (cwd == NULL)
  66     return NULL;
  67
  68   if (strlen (cwd) <= MAX_SAFE_LEN || same_name (cwd, "."))
  69     return cwd;
  70
  71   free (cwd);
  72   errno = ENAMETOOLONG;
  73   return NULL;
  74 }