elf/chroot_canon.c

   1 /* Return the canonical absolute name of a given file inside chroot.
   2    Copyright (C) 1996, 1997, 1998, 1999, 2000, 2001, 2004
   3    Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <stdlib.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <limits.h>
  25 #include <sys/param.h>
  26 #include <sys/stat.h>
  27 #include <errno.h>
  28 #include <stddef.h>
  29 #include <stdint.h>
  30
  31 #include "ldconfig.h"
  32
  33 #ifndef PATH_MAX
  34 #define PATH_MAX 1024
  35 #endif
  36
  37 /* Return the canonical absolute name of file NAME as if chroot(CHROOT) was
  38    done first.  A canonical name does not contain any `.', `..' components
  39    nor any repeated path separators ('/') or symlinks.  All path components
  40    must exist and NAME must be absolute filename.  The result is malloc'd.
  41    The returned name includes the CHROOT prefix.  */
  42
  43 char *
  44 chroot_canon (const char *chroot, const char *name)
  45 {
  46   char *rpath;
  47   char *dest;
  48   char *extra_buf = NULL;
  49   char *rpath_root;
  50   const char *start;
  51   const char *end;
  52   const char *rpath_limit;
  53   int num_links = 0;
  54   size_t chroot_len = strlen (chroot);
  55
  56   if (chroot_len < 1)
  57     {
  58       __set_errno (EINVAL);
  59       return NULL;
  60     }
  61
  62   rpath = malloc (chroot_len + PATH_MAX);
  63   if (rpath == NULL)
  64     return NULL;
  65
  66   rpath_limit = rpath + chroot_len + PATH_MAX;
  67
  68   rpath_root = (char *) mempcpy (rpath, chroot, chroot_len) - 1;
  69   if (*rpath_root != '/')
  70     *++rpath_root = '/';
  71   dest = rpath_root + 1;
  72
  73   for (start = end = name; *start; start = end)
  74     {
  75       struct stat64 st;
  76       int n;
  77
  78       /* Skip sequence of multiple path-separators.  */
  79       while (*start == '/')
  80         ++start;
  81
  82       /* Find end of path component.  */
  83       for (end = start; *end && *end != '/'; ++end)
  84         /* Nothing.  */;
  85
  86       if (end - start == 0)
  87         break;
  88       else if (end - start == 1 && start[0] == '.')
  89         /* nothing */;
  90       else if (end - start == 2 && start[0] == '.' && start[1] == '.')
  91         {
  92           /* Back up to previous component, ignore if at root already.  */
  93           if (dest > rpath_root + 1)
  94             while ((--dest)[-1] != '/');
  95         }
  96       else
  97         {
  98           size_t new_size;
  99
 100           if (dest[-1] != '/')
 101             *dest++ = '/';
 102
 103           if (dest + (end - start) >= rpath_limit)
 104             {
 105               ptrdiff_t dest_offset = dest - rpath;
 106               char *new_rpath;
 107
 108               new_size = rpath_limit - rpath;
 109               if (end - start + 1 > PATH_MAX)
 110                 new_size += end - start + 1;
 111               else
 112                 new_size += PATH_MAX;
 113               new_rpath = (char *) realloc (rpath, new_size);
 114               if (new_rpath == NULL)
 115                 goto error;
 116               rpath = new_rpath;
 117               rpath_limit = rpath + new_size;
 118
 119               dest = rpath + dest_offset;
 120             }
 121
 122           dest = mempcpy (dest, start, end - start);
 123           *dest = '\0';
 124
 125           if (lstat64 (rpath, &st) < 0)
 126             {
 127               if (*end == '\0')
 128                 goto done;
 129               goto error;
 130             }
 131
 132           if (S_ISLNK (st.st_mode))
 133             {
 134               char *buf = alloca (PATH_MAX);
 135               size_t len;
 136
 137               if (++num_links > MAXSYMLINKS)
 138                 {
 139                   __set_errno (ELOOP);
 140                   goto error;
 141                 }
 142
 143               n = readlink (rpath, buf, PATH_MAX);
 144               if (n < 0)
 145                 {
 146                   if (*end == '\0')
 147                     goto done;
 148                   goto error;
 149                 }
 150               buf[n] = '\0';
 151
 152               if (!extra_buf)
 153                 extra_buf = alloca (PATH_MAX);
 154
 155               len = strlen (end);
 156               if ((long int) (n + len) >= PATH_MAX)
 157                 {
 158                   __set_errno (ENAMETOOLONG);
 159                   goto error;
 160                 }
 161
 162               /* Careful here, end may be a pointer into extra_buf... */
 163               memmove (&extra_buf[n], end, len + 1);
 164               name = end = memcpy (extra_buf, buf, n);
 165
 166               if (buf[0] == '/')
 167                 dest = rpath_root + 1;  /* It's an absolute symlink */
 168               else
 169                 /* Back up to previous component, ignore if at root already: */
 170                 if (dest > rpath_root + 1)
 171                   while ((--dest)[-1] != '/');
 172             }
 173         }
 174     }
 175  done:
 176   if (dest > rpath_root + 1 && dest[-1] == '/')
 177     --dest;
 178   *dest = '\0';
 179
 180   return rpath;
 181
 182  error:
 183   free (rpath);
 184   return NULL;
 185 }