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Re: [PATCH] Mangle NULL pointers in iconv/gconv [BZ #22025]


On 08/29/2017 09:28 AM, Florian Weimer wrote:
> We have been carrying the attached patch for a while.
> 
> There is no test because triggering this failure is very hard even on 32
> bit.
> 
> Based on my review, it fixes all NULL pointer inconsistencies except the
> mangling of __end_fct after a gconv_init failure.  While writing a test
> for this omission I found a heap corruption, so I filed a separate bug
> for these remaining issues:
> 
>   <https://sourceware.org/bugzilla/show_bug.cgi?id=22026>

This looks good to me.

It deletes the silly NULL checking code, and makes us consistently
managle and demangle which is conceptualy easier to understand.

> gconv: Consistently mangle NULL function pointers [BZ #22025]
> 
> Not mangling NULL pointers is not safe because with very low
> probability, a non-NULL function pointer can turn into a NULL pointer
> after mangling.
> 
> 2017-08-29  Patsy Franklin  <pfrankli@redhat.com>
> 	    Jeff Law  <law@redhat.com>
> 
> 	[BZ #22025]
> 	Mangle NULL pointers in iconv/gconv.
> 	* iconv/gconv_cache.c (find_module): Demangle init_fct before
> 	checking for NULL. Mangle __btowc_fct if init_fct is non-NULL.
> 	* iconv/gconv_db.c (free_derivation): Check that __shlib_handle
> 	is non-NULL before demangling the end_fct.  Check for NULL
> 	end_fct after demangling.
> 	(__gconv_release_step): Demangle the end_fct before checking
> 	it for NULL.   Remove assert on __shlibc_handle != NULL.
> 	(gen_steps): Don't check btowc_fct for NULL before mangling.
> 	Demangle init_fct before checking for NULL.
> 	(increment_counter): Likewise.
> 	* gconv_dl.c (__gconv_find_shlib): Don't check init_fct or
> 	end_fct for NULL before mangling.
> 	* wcsmbs/btowc.c (__btowc): Demangle btowc_fct before checking
> 	for NULL.
> 
> diff --git a/iconv/gconv_cache.c b/iconv/gconv_cache.c
> index d6a47de838..7d2751a506 100644
> --- a/iconv/gconv_cache.c
> +++ b/iconv/gconv_cache.c
> @@ -207,17 +207,16 @@ find_module (const char *directory, const char *filename,
>        result->__data = NULL;
>  
>        /* Call the init function.  */
> -      if (result->__init_fct != NULL)
> -	{
> -	  __gconv_init_fct init_fct = result->__init_fct;
> +      __gconv_init_fct init_fct = result->__init_fct;
>  #ifdef PTR_DEMANGLE
> -	  PTR_DEMANGLE (init_fct);
> +      PTR_DEMANGLE (init_fct);

OK.

>  #endif
> +      if (init_fct != NULL)
> +	{
>  	  status = DL_CALL_FCT (init_fct, (result));
>  
>  #ifdef PTR_MANGLE
> -	  if (result->__btowc_fct != NULL)
> -	    PTR_MANGLE (result->__btowc_fct);
> +	  PTR_MANGLE (result->__btowc_fct);

OK.

>  #endif
>  	}
>      }
> diff --git a/iconv/gconv_db.c b/iconv/gconv_db.c
> index 7893fadba1..b748467de5 100644
> --- a/iconv/gconv_db.c
> +++ b/iconv/gconv_db.c
> @@ -179,16 +179,15 @@ free_derivation (void *p)
>    size_t cnt;
>  
>    for (cnt = 0; cnt < deriv->nsteps; ++cnt)
> -    if (deriv->steps[cnt].__counter > 0
> -	&& deriv->steps[cnt].__end_fct != NULL)
> +    if ((deriv->steps[cnt].__counter > 0)
> +	&& (deriv->steps[cnt].__shlib_handle != NULL))

OK.

>        {
> -	assert (deriv->steps[cnt].__shlib_handle != NULL);

OK.

> -
>  	__gconv_end_fct end_fct = deriv->steps[cnt].__end_fct;
>  #ifdef PTR_DEMANGLE
>  	PTR_DEMANGLE (end_fct);
>  #endif
> -	DL_CALL_FCT (end_fct, (&deriv->steps[cnt]));
> +	if (end_fct != NULL)
> +	  DL_CALL_FCT (end_fct, (&deriv->steps[cnt]));

OK.

>        }
>  
>    /* Free the name strings.  */
> @@ -212,16 +211,12 @@ __gconv_release_step (struct __gconv_step *step)
>    if (step->__shlib_handle != NULL && --step->__counter == 0)
>      {
>        /* Call the destructor.  */
> -      if (step->__end_fct != NULL)
> -	{
> -	  assert (step->__shlib_handle != NULL);
> -
> -	  __gconv_end_fct end_fct = step->__end_fct;
> +	__gconv_end_fct end_fct = step->__end_fct;

OK.

>  #ifdef PTR_DEMANGLE
> -	  PTR_DEMANGLE (end_fct);
> +	PTR_DEMANGLE (end_fct);

OK.

>  #endif
> -	  DL_CALL_FCT (end_fct, (step));
> -	}
> +      if (end_fct != NULL)
> +	DL_CALL_FCT (end_fct, (step));

OK.

>  
>  #ifndef STATIC_GCONV
>        /* Release the loaded module.  */
> @@ -313,13 +308,11 @@ gen_steps (struct derivation_step *best, const char *toset,
>  
>  	      /* Call the init function.  */
>  	      __gconv_init_fct init_fct = result[step_cnt].__init_fct;
> -	      if (init_fct != NULL)
> -		{
> -		  assert (result[step_cnt].__shlib_handle != NULL);
> -
>  # ifdef PTR_DEMANGLE
> -		  PTR_DEMANGLE (init_fct);
> +	      PTR_DEMANGLE (init_fct);
>  # endif

OK.

> +	      if (init_fct != NULL)
> +		{
>  		  status = DL_CALL_FCT (init_fct, (&result[step_cnt]));
>  
>  		  if (__builtin_expect (status, __GCONV_OK) != __GCONV_OK)
> @@ -332,8 +325,7 @@ gen_steps (struct derivation_step *best, const char *toset,
>  		    }
>  
>  # ifdef PTR_MANGLE
> -		  if (result[step_cnt].__btowc_fct != NULL)
> -		    PTR_MANGLE (result[step_cnt].__btowc_fct);
> +		  PTR_MANGLE (result[step_cnt].__btowc_fct);

OK.

>  # endif
>  		}
>  	    }
> @@ -415,16 +407,15 @@ increment_counter (struct __gconv_step *steps, size_t nsteps)
>  
>  	  /* Call the init function.  */
>  	  __gconv_init_fct init_fct = step->__init_fct;
> +#ifdef PTR_DEMANGLE
> +	  PTR_DEMANGLE (init_fct);
> +#endif
>  	  if (init_fct != NULL)
>  	    {
> -#ifdef PTR_DEMANGLE
> -	      PTR_DEMANGLE (init_fct);
> -#endif


OK.

>  	      DL_CALL_FCT (init_fct, (step));
>  
>  #ifdef PTR_MANGLE
> -	      if (step->__btowc_fct != NULL)
> -		PTR_MANGLE (step->__btowc_fct);
> +	      PTR_MANGLE (step->__btowc_fct);

OK.

>  #endif
>  	    }
>  	}
> diff --git a/iconv/gconv_dl.c b/iconv/gconv_dl.c
> index 241836204d..d7dbba90a2 100644
> --- a/iconv/gconv_dl.c
> +++ b/iconv/gconv_dl.c
> @@ -131,10 +131,8 @@ __gconv_find_shlib (const char *name)
>  
>  #ifdef PTR_MANGLE
>  		  PTR_MANGLE (found->fct);
> -		  if (found->init_fct != NULL)
> -		    PTR_MANGLE (found->init_fct);
> -		  if (found->end_fct !=  NULL)
> -		    PTR_MANGLE (found->end_fct);
> +		  PTR_MANGLE (found->init_fct);
> +		  PTR_MANGLE (found->end_fct);

OK.

>  #endif
>  
>  		  /* We have succeeded in loading the shared object.  */
> diff --git a/wcsmbs/btowc.c b/wcsmbs/btowc.c
> index 22464dc5e2..97fb7170f3 100644
> --- a/wcsmbs/btowc.c
> +++ b/wcsmbs/btowc.c
> @@ -46,15 +46,15 @@ __btowc (int c)
>    /* Get the conversion functions.  */
>    fcts = get_gconv_fcts (_NL_CURRENT_DATA (LC_CTYPE));
>    __gconv_btowc_fct btowc_fct = fcts->towc->__btowc_fct;
> +#ifdef PTR_DEMANGLE
> +  if (fcts->towc->__shlib_handle != NULL)
> +    PTR_DEMANGLE (btowc_fct);
> +#endif

OK.

>  
>    if (__builtin_expect (fcts->towc_nsteps == 1, 1)
>        && __builtin_expect (btowc_fct != NULL, 1))
>      {
>        /* Use the shortcut function.  */
> -#ifdef PTR_DEMANGLE
> -      if (fcts->towc->__shlib_handle != NULL)
> -	PTR_DEMANGLE (btowc_fct);
> -#endif

OK.

>        return DL_CALL_FCT (btowc_fct, (fcts->towc, (unsigned char) c));
>      }
>    else


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