elf/chroot_canon.c

   1 /* Return the canonical absolute name of a given file inside chroot.
   2    Copyright (C) 1996, 1997, 1998, 1999, 2000 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 #include <stdint.h>
  29
  30 #include "ldconfig.h"
  31
  32 #ifndef PATH_MAX
  33 #define PATH_MAX 1024
  34 #endif
  35
  36 /* Return the canonical absolute name of file NAME as if chroot(CHROOT) was
  37    done first.  A canonical name does not contain any `.', `..' components
  38    nor any repeated path separators ('/') or symlinks.  All path components
  39    must exist and NAME must be absolute filename.  The result is malloc'd.
  40    The returned name includes the CHROOT prefix.  */
  41
  42 char *
  43 chroot_canon (const char *chroot, const char *name)
  44 {
  45   char *rpath, *dest, *extra_buf = NULL, *rpath_root;
  46   const char *start, *end, *rpath_limit;
  47   int num_links = 0;
  48   size_t chroot_len = strlen (chroot);
  49
  50   if (chroot_len < 1)
  51     {
  52       __set_errno (EINVAL);
  53       return NULL;
  54     }
  55
  56   rpath = malloc (chroot_len + PATH_MAX);
  57   rpath_limit = rpath + chroot_len + PATH_MAX;
  58
  59   rpath_root = (char *) mempcpy (rpath, chroot, chroot_len) - 1;
  60   if (*rpath_root != '/')
  61     *++rpath_root = '/';
  62   dest = rpath_root + 1;
  63
  64   for (start = end = name; *start; start = end)
  65     {
  66       struct stat64 st;
  67       int n;
  68
  69       /* Skip sequence of multiple path-separators.  */
  70       while (*start == '/')
  71         ++start;
  72
  73       /* Find end of path component.  */
  74       for (end = start; *end && *end != '/'; ++end)
  75         /* Nothing.  */;
  76
  77       if (end - start == 0)
  78         break;
  79       else if (end - start == 1 && start[0] == '.')
  80         /* nothing */;
  81       else if (end - start == 2 && start[0] == '.' && start[1] == '.')
  82         {
  83           /* Back up to previous component, ignore if at root already.  */
  84           if (dest > rpath_root + 1)
  85             while ((--dest)[-1] != '/');
  86         }
  87       else
  88         {
  89           size_t new_size;
  90
  91           if (dest[-1] != '/')
  92             *dest++ = '/';
  93
  94           if (dest + (end - start) >= rpath_limit)
  95             {
  96               ptrdiff_t dest_offset = dest - rpath;
  97
  98               new_size = rpath_limit - rpath;
  99               if (end - start + 1 > PATH_MAX)
 100                 new_size += end - start + 1;
 101               else
 102                 new_size += PATH_MAX;
 103               rpath = realloc (rpath, new_size);
 104               rpath_limit = rpath + new_size;
 105               if (rpath == NULL)
 106                 return NULL;
 107
 108               dest = rpath + dest_offset;
 109             }
 110
 111           dest = mempcpy (dest, start, end - start);
 112           *dest = '\0';
 113
 114           if (lstat64 (rpath, &st) < 0)
 115             {
 116               if (*end == '\0')
 117                 goto done;
 118               goto error;
 119             }
 120
 121           if (S_ISLNK (st.st_mode))
 122             {
 123               char *buf = alloca (PATH_MAX);
 124               size_t len;
 125
 126               if (++num_links > MAXSYMLINKS)
 127                 {
 128                   __set_errno (ELOOP);
 129                   goto error;
 130                 }
 131
 132               n = readlink (rpath, buf, PATH_MAX);
 133               if (n < 0)
 134                 {
 135                   if (*end == '\0')
 136                     goto done;
 137                   goto error;
 138                 }
 139               buf[n] = '\0';
 140
 141               if (!extra_buf)
 142                 extra_buf = alloca (PATH_MAX);
 143
 144               len = strlen (end);
 145               if ((long int) (n + len) >= PATH_MAX)
 146                 {
 147                   __set_errno (ENAMETOOLONG);
 148                   goto error;
 149                 }
 150
 151               /* Careful here, end may be a pointer into extra_buf... */
 152               memmove (&extra_buf[n], end, len + 1);
 153               name = end = memcpy (extra_buf, buf, n);
 154
 155               if (buf[0] == '/')
 156                 dest = rpath_root + 1;  /* It's an absolute symlink */
 157               else
 158                 /* Back up to previous component, ignore if at root already: */
 159                 if (dest > rpath_root + 1)
 160                   while ((--dest)[-1] != '/');
 161             }
 162         }
 163     }
 164  done:
 165   if (dest > rpath_root + 1 && dest[-1] == '/')
 166     --dest;
 167   *dest = '\0';
 168
 169   return rpath;
 170
 171  error:
 172   free (rpath);
 173   return NULL;
 174 }