stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2    Copyright (C) 1996,1997,1998,1999,2000,2001 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 <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <limits.h>
  24 #include <sys/param.h>
  25 #include <sys/stat.h>
  26 #include <errno.h>
  27 #include <stddef.h>
  28
  29 /* Return the canonical absolute name of file NAME.  A canonical name
  30    does not contain any `.', `..' components nor any repeated path
  31    separators ('/') or symlinks.  All path components must exist.  If
  32    RESOLVED is null, the result is malloc'd; otherwise, if the
  33    canonical name is PATH_MAX chars or more, returns null with `errno'
  34    set to ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars,
  35    returns the name in RESOLVED.  If the name cannot be resolved and
  36    RESOLVED is non-NULL, it contains the path of the first component
  37    that cannot be resolved.  If the path can be resolved, RESOLVED
  38    holds the same value as the value returned.  */
  39
  40 static char *
  41 canonicalize (const char *name, char *resolved)
  42 {
  43   char *rpath, *dest, *extra_buf = NULL;
  44   const char *start, *end, *rpath_limit;
  45   long int path_max;
  46   int num_links = 0;
  47
  48   if (name == NULL)
  49     {
  50       /* As per Single Unix Specification V2 we must return an error if
  51          either parameter is a null pointer.  We extend this to allow
  52          the RESOLVED parameter to be NULL in case the we are expected to
  53          allocate the room for the return value.  */
  54       __set_errno (EINVAL);
  55       return NULL;
  56     }
  57
  58   if (name[0] == '\0')
  59     {
  60       /* As per Single Unix Specification V2 we must return an error if
  61          the name argument points to an empty string.  */
  62       __set_errno (ENOENT);
  63       return NULL;
  64     }
  65
  66 #ifdef PATH_MAX
  67   path_max = PATH_MAX;
  68 #else
  69   path_max = pathconf (name, _PC_PATH_MAX);
  70   if (path_max <= 0)
  71     path_max = 1024;
  72 #endif
  73
  74   rpath = resolved ? __alloca (path_max) : malloc (path_max);
  75   rpath_limit = rpath + path_max;
  76
  77   if (name[0] != '/')
  78     {
  79       if (!__getcwd (rpath, path_max))
  80         {
  81           rpath[0] = '\0';
  82           goto error;
  83         }
  84       dest = strchr (rpath, '\0');
  85     }
  86   else
  87     {
  88       rpath[0] = '/';
  89       dest = rpath + 1;
  90     }
  91
  92   for (start = end = name; *start; start = end)
  93     {
  94       struct stat64 st;
  95       int n;
  96
  97       /* Skip sequence of multiple path-separators.  */
  98       while (*start == '/')
  99         ++start;
 100
 101       /* Find end of path component.  */
 102       for (end = start; *end && *end != '/'; ++end)
 103         /* Nothing.  */;
 104
 105       if (end - start == 0)
 106         break;
 107       else if (end - start == 1 && start[0] == '.')
 108         /* nothing */;
 109       else if (end - start == 2 && start[0] == '.' && start[1] == '.')
 110         {
 111           /* Back up to previous component, ignore if at root already.  */
 112           if (dest > rpath + 1)
 113             while ((--dest)[-1] != '/');
 114         }
 115       else
 116         {
 117           size_t new_size;
 118
 119           if (dest[-1] != '/')
 120             *dest++ = '/';
 121
 122           if (dest + (end - start) >= rpath_limit)
 123             {
 124               ptrdiff_t dest_offset = dest - rpath;
 125               char *new_rpath;
 126
 127               if (resolved)
 128                 {
 129                   __set_errno (ENAMETOOLONG);
 130                   if (dest > rpath + 1)
 131                     dest--;
 132                   *dest = '\0';
 133                   goto error;
 134                 }
 135               new_size = rpath_limit - rpath;
 136               if (end - start + 1 > path_max)
 137                 new_size += end - start + 1;
 138               else
 139                 new_size += path_max;
 140               new_rpath = (char *) realloc (rpath, new_size);
 141               if (new_rpath == NULL)
 142                 goto error;
 143               rpath = new_rpath;
 144               rpath_limit = rpath + new_size;
 145
 146               dest = rpath + dest_offset;
 147             }
 148
 149           dest = __mempcpy (dest, start, end - start);
 150           *dest = '\0';
 151
 152           if (__lxstat64 (_STAT_VER, rpath, &st) < 0)
 153             goto error;
 154
 155           if (S_ISLNK (st.st_mode))
 156             {
 157               char *buf = __alloca (path_max);
 158               size_t len;
 159
 160               if (++num_links > MAXSYMLINKS)
 161                 {
 162                   __set_errno (ELOOP);
 163                   goto error;
 164                 }
 165
 166               n = __readlink (rpath, buf, path_max);
 167               if (n < 0)
 168                 goto error;
 169               buf[n] = '\0';
 170
 171               if (!extra_buf)
 172                 extra_buf = __alloca (path_max);
 173
 174               len = strlen (end);
 175               if ((long int) (n + len) >= path_max)
 176                 {
 177                   __set_errno (ENAMETOOLONG);
 178                   goto error;
 179                 }
 180
 181               /* Careful here, end may be a pointer into extra_buf... */
 182               memmove (&extra_buf[n], end, len + 1);
 183               name = end = memcpy (extra_buf, buf, n);
 184
 185               if (buf[0] == '/')
 186                 dest = rpath + 1;       /* It's an absolute symlink */
 187               else
 188                 /* Back up to previous component, ignore if at root already: */
 189                 if (dest > rpath + 1)
 190                   while ((--dest)[-1] != '/');
 191             }
 192         }
 193     }
 194   if (dest > rpath + 1 && dest[-1] == '/')
 195     --dest;
 196   *dest = '\0';
 197
 198   return resolved ? memcpy (resolved, rpath, dest - rpath + 1) : rpath;
 199
 200 error:
 201   if (resolved)
 202     strcpy (resolved, rpath);
 203   else
 204     free (rpath);
 205   return NULL;
 206 }
 207
 208
 209 char *
 210 __realpath (const char *name, char *resolved)
 211 {
 212   if (resolved == NULL)
 213     {
 214       __set_errno (EINVAL);
 215       return NULL;
 216     }
 217
 218   return canonicalize (name, resolved);
 219 }
 220 weak_alias (__realpath, realpath)
 221
 222
 223 char *
 224 __canonicalize_file_name (const char *name)
 225 {
 226   return canonicalize (name, NULL);
 227 }
 228 weak_alias (__canonicalize_file_name, canonicalize_file_name)