[libpng16] Fix potential problem with bKGD (Cosmin Truta)

pngrutil.c

 
 /* pngrutil.c - utilities to read a PNG file
  *
- * Last changed in libpng 1.6.33 [September 28, 2017]
- * Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.35 [(PENDING RELEASE)]
+ * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
@@ -1997,6 +1997,15 @@ png_handle_bKGD(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
 
    else if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0) /* GRAY */
    {
+      if (png_ptr->bit_depth <= 8)
+      {
+         if (buf[0] != 0 || buf[1] >= (unsigned int)(1 << png_ptr->bit_depth))
+         {
+            png_chunk_benign_error(png_ptr, "invalid gray level");
+            return;
+         }
+      }
+
       background.index = 0;
       background.red =
       background.green =
@@ -2006,6 +2015,15 @@ png_handle_bKGD(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
 
    else
    {
+      if (png_ptr->bit_depth <= 8)
+      {
+         if (buf[0] != 0 || buf[2] != 0 || buf[4] != 0)
+         {
+            png_chunk_benign_error(png_ptr, "invalid color");
+            return;
+         }
+      }
+
       background.index = 0;
       background.red = png_get_uint_16(buf);
       background.green = png_get_uint_16(buf + 2);