From 96333b6bea59dd8d0659e46ec9426119d3fe5753 Mon Sep 17 00:00:00 2001
From: Glenn Randers-Pehrson <glennrp at users.sourceforge.net>
Date: Sat, 23 Sep 2017 10:34:40 -0500
Subject: [PATCH] [libpng16] Defeat optimization that removes reading rows in
 the fuzzer.

---
 contrib/oss-fuzz/libpng_read_fuzzer.cc | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/contrib/oss-fuzz/libpng_read_fuzzer.cc b/contrib/oss-fuzz/libpng_read_fuzzer.cc
index b17681b40..efd8cf16a 100644
--- a/contrib/oss-fuzz/libpng_read_fuzzer.cc
+++ b/contrib/oss-fuzz/libpng_read_fuzzer.cc
@@ -5,7 +5,7 @@
 // Use of this source code is governed by a BSD-style license that may
 // be found in the LICENSE file https://cs.chromium.org/chromium/src/LICENSE
 
-// Last changed in libpng 1.6.33beta03 [September 20, 2017]
+// Last changed in libpng 1.6.33beta03 [September 23, 2017]
 
 // The modifications in 2017 by Glenn Randers-Pehrson include
 // 1. addition of a PNG_CLEANUP macro,
@@ -169,13 +169,21 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   int passes = png_set_interlace_handling(png_handler.png_ptr);
   png_start_read_image(png_handler.png_ptr);
 
+  int max_filter = 0;
   for (int pass = 0; pass < passes; ++pass) {
     for (png_uint_32 y = 0; y < height; ++y) {
       png_read_row(png_handler.png_ptr,
                    static_cast<png_bytep>(png_handler.row_ptr), nullptr);
+      max_filter = png_handler.row_buf[0] > max_filter ?
+        png_handler.row_buf[0] : max_filter;
     }
   }
 
+  if (max_filter > 5) {
+    PNG_CLEANUP
+    return 0;
+  }
+
   png_read_end(png_handler.png_ptr, png_handler.end_info_ptr);
 
   PNG_CLEANUP