Re: [PATCH v1.1] __gconv_translit_find: Actually append ".so" to module name [BZ #17187]

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Thu, Aug 21, 2014 at 07:33:03PM +0200, Florian Weimer wrote:
> On 07/21/2014 03:01 PM, Florian Weimer wrote:
> >The previous code wrote the string after the terminating NUL character
> >of the existing module name.  This had two effects: the ".so" extension
> >was not actually visible in the module name string, and a NUL byte was
> >written byond the end of the allocated buffer.
> >
> >I'm not sure how to add a functionality test for this.  The test suite
> >does not show any changes in behavior.
> 
> The attached version of this patch is suitable for backporting and disables
> external module loading, rather than attempting to fix it.  The tests for
> the internal transliteration functionality still pass.
> 
> I would like to suggest to put this in master, and include the second,
> larger patch as a clean-up after the 2.20 release.

The update here is that there is now a live privilege escalation
exploit[1] for 32-bit Fedora 20 and it may not be too hard to port the
exploit to more platforms.

I think this fix is fine (except a minor nit below), but it would be
good if another maintainer also verifies that it won't break anything.
Also, Allan needs to ack it for 2.20.  I am going to put the patch in
rawhide today anyway, so I'll report back if there are any issues; I
don't expect any though.

> 
> -- 
> Florian Weimer / Red Hat Product Security

> 2014-08-21  Florian Weimer  <fweimer@redhat.com>
> 
> 	[BZ #17187]
> 	* iconv/gconv_trans.c (struct known_trans, search_tree, lock,
> 	trans_compare, open_translit, __gconv_translit_find):
> 	Remove module loading code.
> 
> diff --git a/NEWS b/NEWS
> index 28da6e5..6d8529c 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -23,7 +23,7 @@ Version 2.20
>    16966, 16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031,
>    17042, 17048, 17050, 17058, 17061, 17062, 17069, 17075, 17078, 17079,
>    17084, 17086, 17088, 17092, 17097, 17125, 17135, 17137, 17150, 17153,
> -  17213, 17259, 17261, 17262, 17263.
> +  17187, 17213, 17259, 17261, 17262, 17263.
>  
>  * Reverted change of ABI data structures for s390 and s390x:
>    On s390 and s390x the size of struct ucontext and jmp_buf was increased in
> @@ -108,6 +108,10 @@ Version 2.20
>    handle the new instruction encodings.  This is known to affect Valgrind
>    versions up through 3.9 (but will be fixed in the forthcoming 3.10
>    release), and might affect other tools that do instruction emulation.
> +
> +* Support for loadable gconv transliteration modules has been removed
> +  because it did not work at all.  Regular gconv conversion modules are
> +  still supported.  (CVE-2014-5119)
>  
>  Version 2.19
>  
> diff --git a/iconv/gconv_trans.c b/iconv/gconv_trans.c
> index 1e25854..d71c029 100644
> --- a/iconv/gconv_trans.c
> +++ b/iconv/gconv_trans.c
> @@ -238,181 +238,11 @@ __gconv_transliterate (struct __gconv_step *step,
>    return __GCONV_ILLEGAL_INPUT;
>  }
>  
> -
> -/* Structure to represent results of found (or not) transliteration
> -   modules.  */
> -struct known_trans
> -{
> -  /* This structure must remain the first member.  */
> -  struct trans_struct info;
> -
> -  char *fname;
> -  void *handle;
> -  int open_count;
> -};
> -
> -
> -/* Tree with results of previous calls to __gconv_translit_find.  */
> -static void *search_tree;
> -
> -/* We modify global data.   */
> -__libc_lock_define_initialized (static, lock);
> -
> -
> -/* Compare two transliteration entries.  */
> -static int
> -trans_compare (const void *p1, const void *p2)
> -{
> -  const struct known_trans *s1 = (const struct known_trans *) p1;
> -  const struct known_trans *s2 = (const struct known_trans *) p2;
> -
> -  return strcmp (s1->info.name, s2->info.name);
> -}
> -
> -
> -/* Open (maybe reopen) the module named in the struct.  Get the function
> -   and data structure pointers we need.  */
> -static int
> -open_translit (struct known_trans *trans)
> -{
> -  __gconv_trans_query_fct queryfct;
> -
> -  trans->handle = __libc_dlopen (trans->fname);
> -  if (trans->handle == NULL)
> -    /* Not available.  */
> -    return 1;
> -
> -  /* Find the required symbol.  */
> -  queryfct = __libc_dlsym (trans->handle, "gconv_trans_context");
> -  if (queryfct == NULL)
> -    {
> -      /* We cannot live with that.  */
> -    close_and_out:
> -      __libc_dlclose (trans->handle);
> -      trans->handle = NULL;
> -      return 1;
> -    }
> -
> -  /* Get the context.  */
> -  if (queryfct (trans->info.name, &trans->info.csnames, &trans->info.ncsnames)
> -      != 0)
> -    goto close_and_out;
> -
> -  /* Of course we also have to have the actual function.  */
> -  trans->info.trans_fct = __libc_dlsym (trans->handle, "gconv_trans");
> -  if (trans->info.trans_fct == NULL)
> -    goto close_and_out;
> -
> -  /* Now the optional functions.  */
> -  trans->info.trans_init_fct =
> -    __libc_dlsym (trans->handle, "gconv_trans_init");
> -  trans->info.trans_context_fct =
> -    __libc_dlsym (trans->handle, "gconv_trans_context");
> -  trans->info.trans_end_fct =
> -    __libc_dlsym (trans->handle, "gconv_trans_end");
> -
> -  trans->open_count = 1;
> -
> -  return 0;
> -}
> -
> -
>  int
>  internal_function
>  __gconv_translit_find (struct trans_struct *trans)
>  {
> -  struct known_trans **found;
> -  const struct path_elem *runp;
> -  int res = 1;
> -
> -  /* We have to have a name.  */
> -  assert (trans->name != NULL);
> -
> -  /* Acquire the lock.  */
> -  __libc_lock_lock (lock);
> -
> -  /* See whether we know this module already.  */
> -  found = __tfind (trans, &search_tree, trans_compare);
> -  if (found != NULL)
> -    {
> -      /* Is this module available?  */
> -      if ((*found)->handle != NULL)
> -	{
> -	  /* Maybe we have to reopen the file.  */
> -	  if ((*found)->handle != (void *) -1)
> -	    /* The object is not unloaded.  */
> -	    res = 0;
> -	  else if (open_translit (*found) == 0)
> -	    {
> -	      /* Copy the data.  */
> -	      *trans = (*found)->info;
> -	      (*found)->open_count++;
> -	      res = 0;
> -	    }
> -	}
> -    }
> -  else
> -    {
> -      size_t name_len = strlen (trans->name) + 1;
> -      int need_so = 0;
> -      struct known_trans *newp;
> -
> -      /* We have to continue looking for the module.  */
> -      if (__gconv_path_elem == NULL)
> -	__gconv_get_path ();
> -
> -      /* See whether we have to append .so.  */
> -      if (name_len <= 4 || memcmp (&trans->name[name_len - 4], ".so", 3) != 0)
> -	need_so = 1;
> -
> -      /* Create a new entry.  */
> -      newp = (struct known_trans *) malloc (sizeof (struct known_trans)
> -					    + (__gconv_max_path_elem_len
> -					       + name_len + 3)
> -					    + name_len);
> -      if (newp != NULL)
> -	{
> -	  char *cp;
> -
> -	  /* Clear the struct.  */
> -	  memset (newp, '\0', sizeof (struct known_trans));
> -
> -	  /* Store a copy of the module name.  */
> -	  newp->info.name = cp = (char *) (newp + 1);
> -	  cp = __mempcpy (cp, trans->name, name_len);
> -
> -	  newp->fname = cp;
> -
> -	  /* Search in all the directories.  */
> -	  for (runp = __gconv_path_elem; runp->name != NULL; ++runp)
> -	    {
> -	      cp = __mempcpy (__stpcpy ((char *) newp->fname, runp->name),
> -			      trans->name, name_len);
> -	      if (need_so)
> -		memcpy (cp, ".so", sizeof (".so"));
> -
> -	      if (open_translit (newp) == 0)
> -		{
> -		  /* We found a module.  */
> -		  res = 0;
> -		  break;
> -		}
> -	    }
> -
> -	  if (res)
> -	    newp->fname = NULL;
> -
> -	  /* In any case we'll add the entry to our search tree.  */
> -	  if (__tsearch (newp, &search_tree, trans_compare) == NULL)
> -	    {
> -	      /* Yickes, this should not happen.  Unload the object.  */
> -	      res = 1;
> -	      /* XXX unload here.  */
> -	    }
> -	}
> -    }
> -
> -  __libc_lock_unlock (lock);
> -
> -  return res;
> +  /* This function always fails.  Transliteration module loading is
> +     not implemented.  */

The comment should reflect the fact that there was an implementation
that we have removed.  It will be clear from the logs, but not
everybody close the code.  So maybe something like this:

/* Transliteration module loading implementation has been removed
   because it never worked and had a serious security flaw.  As a
   result, this function always fails.  */

> +  return 1;
>  }
> -- 
> 1.9.3
> 

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1119128#c9
[2] http://googleprojectzero.blogspot.in/2014/08/the-poisoned-nul-byte-2014-edition.html

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