text: /* Return the canonical absolute name of a given file inside chroot.
     Copyright (C) 1996-2016 Free Software Foundation, Inc.
     This file is part of the GNU C Library.
  
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published
     by the Free Software Foundation; version 2 of the License, or
     (at your option) any later version.
  
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  #include <limits.h>
  #include <sys/stat.h>
  #include <errno.h>
  #include <stddef.h>
  #include <stdint.h>
  
  #include <eloop-threshold.h>
  #include <ldconfig.h>
  
  #ifndef PATH_MAX
  #define PATH_MAX 1024
  #endif
  
  /* Return the canonical absolute name of file NAME as if chroot(CHROOT) was
     done first.  A canonical name does not contain any `.', `..' components
     nor any repeated path separators ('/') or symlinks.  All path components
     must exist and NAME must be absolute filename.  The result is malloc'd.
     The returned name includes the CHROOT prefix.  */
  
  char *
  chroot_canon (const char *chroot, const char *name)
  {
    char *rpath;
    char *dest;
    char *extra_buf = NULL;
    char *rpath_root;
    const char *start;
    const char *end;
    const char *rpath_limit;
    int num_links = 0;
    size_t chroot_len = strlen (chroot);
  
    if (chroot_len < 1)
      {
        __set_errno (EINVAL);
        return NULL;
      }
  
    rpath = xmalloc (chroot_len + PATH_MAX);
  
    rpath_limit = rpath + chroot_len + PATH_MAX;
  
    rpath_root = (char *) mempcpy (rpath, chroot, chroot_len) - 1;
    if (*rpath_root != '/')
      *++rpath_root = '/';
    dest = rpath_root + 1;
  
    for (start = end = name; *start; start = end)
      {
        struct stat64 st;
  
        /* Skip sequence of multiple path-separators.  */
        while (*start == '/')
  	++start;
  
        /* Find end of path component.  */
        for (end = start; *end && *end != '/'; ++end)
  	/* Nothing.  */;
  
        if (end - start == 0)
  	break;
        else if (end - start == 1 && start[0] == '.')
  	/* nothing */;
        else if (end - start == 2 && start[0] == '.' && start[1] == '.')
  	{
  	  /* Back up to previous component, ignore if at root already.  */
  	  if (dest > rpath_root + 1)
  	    while ((--dest)[-1] != '/');
  	}
        else
  	{
  	  size_t new_size;
  
  	  if (dest[-1] != '/')
  	    *dest++ = '/';
  
  	  if (dest + (end - start) >= rpath_limit)
  	    {
  	      ptrdiff_t dest_offset = dest - rpath;
  	      char *new_rpath;
  
  	      new_size = rpath_limit - rpath;
  	      if (end - start + 1 > PATH_MAX)
  		new_size += end - start + 1;
  	      else
  		new_size += PATH_MAX;
  	      new_rpath = (char *) xrealloc (rpath, new_size);
  	      rpath = new_rpath;
  	      rpath_limit = rpath + new_size;
  
  	      dest = rpath + dest_offset;
  	    }
  
  	  dest = mempcpy (dest, start, end - start);
  	  *dest = '\0';
  
  	  if (lstat64 (rpath, &st) < 0)
  	    {
  	      if (*end == '\0')
  		goto done;
  	      goto error;
  	    }
  
  	  if (S_ISLNK (st.st_mode))
  	    {
  	      char *buf = alloca (PATH_MAX);
  	      size_t len;
  
  	      if (++num_links > __eloop_threshold ())
  		{
  		  __set_errno (ELOOP);
  		  goto error;
  		}
  
  	      ssize_t n = readlink (rpath, buf, PATH_MAX - 1);
  	      if (n < 0)
  		{
  		  if (*end == '\0')
  		    goto done;
  		  goto error;
  		}
  	      buf[n] = '\0';
  
  	      if (!extra_buf)
  		extra_buf = alloca (PATH_MAX);
  
  	      len = strlen (end);
  	      if (len >= PATH_MAX - n)
  		{
  		  __set_errno (ENAMETOOLONG);
  		  goto error;
  		}
  
  	      /* Careful here, end may be a pointer into extra_buf... */
  	      memmove (&extra_buf[n], end, len + 1);
  	      name = end = memcpy (extra_buf, buf, n);
  
  	      if (buf[0] == '/')
  		dest = rpath_root + 1;	/* It's an absolute symlink */
  	      else
  		/* Back up to previous component, ignore if at root already: */
  		if (dest > rpath_root + 1)
  		  while ((--dest)[-1] != '/');
  	    }
  	}
      }
   done:
    if (dest > rpath_root + 1 && dest[-1] == '/')
      --dest;
    *dest = '\0';
  
    return rpath;
  
   error:
    free (rpath);
    return NULL;
  }
  