stdlib/canonicalize.c

   1 /* Return the canonical absolute name of a given file.
   2    Copyright (C) 1996-2017 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <limits.h>
  24 #include <sys/stat.h>
  25 #include <errno.h>
  26 #include <stddef.h>
  27
  28 #include <eloop-threshold.h>
  29 #include <shlib-compat.h>
  30
  31 /* Return the canonical absolute name of file NAME.  A canonical name
  32    does not contain any `.', `..' components nor any repeated path
  33    separators ('/') or symlinks.  All path components must exist.  If
  34    RESOLVED is null, the result is malloc'd; otherwise, if the
  35    canonical name is PATH_MAX chars or more, returns null with `errno'
  36    set to ENAMETOOLONG; if the name fits in fewer than PATH_MAX chars,
  37    returns the name in RESOLVED.  If the name cannot be resolved and
  38    RESOLVED is non-NULL, it contains the path of the first component
  39    that cannot be resolved.  If the path can be resolved, RESOLVED
  40    holds the same value as the value returned.  */
  41
  42 char *
  43 __realpath (const char *name, char *resolved)
  44 {
  45   char *rpath, *dest, *extra_buf = NULL;
  46   const char *start, *end, *rpath_limit;
  47   long int path_max;
  48   int num_links = 0;
  49
  50   if (name == NULL)
  51     {
  52       /* As per Single Unix Specification V2 we must return an error if
  53          either parameter is a null pointer.  We extend this to allow
  54          the RESOLVED parameter to be NULL in case the we are expected to
  55          allocate the room for the return value.  */
  56       __set_errno (EINVAL);
  57       return NULL;
  58     }
  59
  60   if (name[0] == '\0')
  61     {
  62       /* As per Single Unix Specification V2 we must return an error if
  63          the name argument points to an empty string.  */
  64       __set_errno (ENOENT);
  65       return NULL;
  66     }
  67
  68 #ifdef PATH_MAX
  69   path_max = PATH_MAX;
  70 #else
  71   path_max = pathconf (name, _PC_PATH_MAX);
  72   if (path_max <= 0)
  73     path_max = 1024;
  74 #endif
  75
  76   if (resolved == NULL)
  77     {
  78       rpath = malloc (path_max);
  79       if (rpath == NULL)
  80         return NULL;
  81     }
  82   else
  83     rpath = resolved;
  84   rpath_limit = rpath + path_max;
  85
  86   if (name[0] != '/')
  87     {
  88       if (!__getcwd (rpath, path_max))
  89         {
  90           rpath[0] = '\0';
  91           goto error;
  92         }
  93       dest = __rawmemchr (rpath, '\0');
  94     }
  95   else
  96     {
  97       rpath[0] = '/';
  98       dest = rpath + 1;
  99     }
 100
 101   for (start = end = name; *start; start = end)
 102     {
 103       struct stat64 st;
 104       int n;
 105
 106       /* Skip sequence of multiple path-separators.  */
 107       while (*start == '/')
 108         ++start;
 109
 110       /* Find end of path component.  */
 111       for (end = start; *end && *end != '/'; ++end)
 112         /* Nothing.  */;
 113
 114       if (end - start == 0)
 115         break;
 116       else if (end - start == 1 && start[0] == '.')
 117         /* nothing */;
 118       else if (end - start == 2 && start[0] == '.' && start[1] == '.')
 119         {
 120           /* Back up to previous component, ignore if at root already.  */
 121           if (dest > rpath + 1)
 122             while ((--dest)[-1] != '/');
 123         }
 124       else
 125         {
 126           size_t new_size;
 127
 128           if (dest[-1] != '/')
 129             *dest++ = '/';
 130
 131           if (dest + (end - start) >= rpath_limit)
 132             {
 133               ptrdiff_t dest_offset = dest - rpath;
 134               char *new_rpath;
 135
 136               if (resolved)
 137                 {
 138                   __set_errno (ENAMETOOLONG);
 139                   if (dest > rpath + 1)
 140                     dest--;
 141                   *dest = '\0';
 142                   goto error;
 143                 }
 144               new_size = rpath_limit - rpath;
 145               if (end - start + 1 > path_max)
 146                 new_size += end - start + 1;
 147               else
 148                 new_size += path_max;
 149               new_rpath = (char *) realloc (rpath, new_size);
 150               if (new_rpath == NULL)
 151                 goto error;
 152               rpath = new_rpath;
 153               rpath_limit = rpath + new_size;
 154
 155               dest = rpath + dest_offset;
 156             }
 157
 158           dest = __mempcpy (dest, start, end - start);
 159           *dest = '\0';
 160
 161           if (__lxstat64 (_STAT_VER, rpath, &st) < 0)
 162             goto error;
 163
 164           if (S_ISLNK (st.st_mode))
 165             {
 166               char *buf = __alloca (path_max);
 167               size_t len;
 168
 169               if (++num_links > __eloop_threshold ())
 170                 {
 171                   __set_errno (ELOOP);
 172                   goto error;
 173                 }
 174
 175               n = __readlink (rpath, buf, path_max - 1);
 176               if (n < 0)
 177                 goto error;
 178               buf[n] = '\0';
 179
 180               if (!extra_buf)
 181                 extra_buf = __alloca (path_max);
 182
 183               len = strlen (end);
 184               if ((long int) (n + len) >= path_max)
 185                 {
 186                   __set_errno (ENAMETOOLONG);
 187                   goto error;
 188                 }
 189
 190               /* Careful here, end may be a pointer into extra_buf... */
 191               memmove (&extra_buf[n], end, len + 1);
 192               name = end = memcpy (extra_buf, buf, n);
 193
 194               if (buf[0] == '/')
 195                 dest = rpath + 1;       /* It's an absolute symlink */
 196               else
 197                 /* Back up to previous component, ignore if at root already: */
 198                 if (dest > rpath + 1)
 199                   while ((--dest)[-1] != '/');
 200             }
 201           else if (!S_ISDIR (st.st_mode) && *end != '\0')
 202             {
 203               __set_errno (ENOTDIR);
 204               goto error;
 205             }
 206         }
 207     }
 208   if (dest > rpath + 1 && dest[-1] == '/')
 209     --dest;
 210   *dest = '\0';
 211
 212   assert (resolved == NULL || resolved == rpath);
 213   return rpath;
 214
 215 error:
 216   assert (resolved == NULL || resolved == rpath);
 217   if (resolved == NULL)
 218     free (rpath);
 219   return NULL;
 220 }
 221 versioned_symbol (libc, __realpath, realpath, GLIBC_2_3);
 222
 223
 224 #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_3)
 225 char *
 226 attribute_compat_text_section
 227 __old_realpath (const char *name, char *resolved)
 228 {
 229   if (resolved == NULL)
 230     {
 231       __set_errno (EINVAL);
 232       return NULL;
 233     }
 234
 235   return __realpath (name, resolved);
 236 }
 237 compat_symbol (libc, __old_realpath, realpath, GLIBC_2_0);
 238 #endif
 239
 240
 241 char *
 242 __canonicalize_file_name (const char *name)
 243 {
 244   return __realpath (name, NULL);
 245 }
 246 weak_alias (__canonicalize_file_name, canonicalize_file_name)