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

[Florian Weimer <fweimer at redhat dot com>]

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>

Thanks,
Florian

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);
 #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);
 #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))
       {
-	assert (deriv->steps[cnt].__shlib_handle != NULL);
-
 	__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]));
       }
 
   /* 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;
 #ifdef PTR_DEMANGLE
-	  PTR_DEMANGLE (end_fct);
+	PTR_DEMANGLE (end_fct);
 #endif
-	  DL_CALL_FCT (end_fct, (step));
-	}
+      if (end_fct != NULL)
+	DL_CALL_FCT (end_fct, (step));
 
 #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
+	      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);
 # 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
 	      DL_CALL_FCT (init_fct, (step));
 
 #ifdef PTR_MANGLE
-	      if (step->__btowc_fct != NULL)
-		PTR_MANGLE (step->__btowc_fct);
+	      PTR_MANGLE (step->__btowc_fct);
 #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);
 #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
 
   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
       return DL_CALL_FCT (btowc_fct, (fcts->towc, (unsigned char) c));
     }
   else