[libpng16] Corrected previous attempt at overflow detection in

png_set_unknown_chunks().

ANNOUNCE

 
-Libpng 1.6.0beta38 - January 10, 2013
+Libpng 1.6.0beta38 - January 17, 2013
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -587,7 +587,8 @@ Version 1.6.0beta37 [January 10, 2013]
   Fixed conceivable but difficult to repro overflow. Also added two test
     programs to generate and test a PNG which should have the problem.
 
-Version 1.6.0beta38 [January 10, 2013]
+Version 1.6.0beta38 [January 17, 2013]
+  Corrected previous attempt at overflow detection in png_set_unknown_chunks().
 
   ===========================================================================
                        NOTICE November 17, 2012:

CHANGES

@@ -4340,7 +4340,8 @@ Version 1.6.0beta37 [January 10, 2013]
   Fixed conceivable but difficult to repro overflow. Also added two test
     programs to generate and test a PNG which should have the problem.
 
-Version 1.6.0beta38 [January 10, 2013]
+Version 1.6.0beta38 [January 17, 2013]
+  Corrected previous attempt at overflow detection in png_set_unknown_chunks().
 
   ===========================================================================
                        NOTICE November 17, 2012:

pngset.c

@@ -1130,7 +1130,7 @@ png_set_unknown_chunks(png_const_structrp png_ptr,
     * limit.
     */
    if (num_unknowns > PNG_UINT_32_MAX - info_ptr->unknown_chunks_num ||
-      num_unknowns > PNG_SIZE_MAX/(sizeof *np) - info_ptr->unknown_chunks_num)
+      num_unknowns + info_ptr->unknown_chunks_num > PNG_SIZE_MAX/(sizeof *np))
    {
       /* This is a benign read error (user limits are disabled and we are about
        * to overflow 2^32 chunks) and an application write error.
@@ -1141,7 +1141,7 @@ png_set_unknown_chunks(png_const_structrp png_ptr,
    }
 
    np = png_voidcast(png_unknown_chunkp, png_malloc(png_ptr,
-       (info_ptr->unknown_chunks_num + (unsigned int)num_unknowns) *
+       (info_ptr->unknown_chunks_num + num_unknowns) *
        (sizeof (png_unknown_chunk))));
 
    memcpy(np, info_ptr->unknown_chunks,