1 files changed, 21 insertions, 3 deletions
diff --git a/contrib/oss-fuzz/libpng_read_fuzzer.cc b/contrib/oss-fuzz/libpng_read_fuzzer.cc
index 7b305509c..0190cf786 100644
--- a/contrib/oss-fuzz/libpng_read_fuzzer.cc
+++ b/contrib/oss-fuzz/libpng_read_fuzzer.cc
@@ -5,8 +5,6 @@
 // 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 1.6.35 [July 15, 2018]
-
 // The modifications in 2017 by Glenn Randers-Pehrson include
 // 1. addition of a PNG_CLEANUP macro,
 // 2. setting the option to ignore ADLER32 checksums,
@@ -17,6 +15,7 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <vector>
@@ -60,7 +59,7 @@ struct PngObjectHandler {
       png_free(png_ptr, row_ptr);
     if (end_info_ptr)
       png_destroy_read_struct(&png_ptr, &info_ptr, &end_info_ptr);
-    else if (info_ptr) 
+    else if (info_ptr)
       png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
     else
       png_destroy_read_struct(&png_ptr, nullptr, nullptr);
@@ -78,6 +77,22 @@ void user_read_data(png_structp png_ptr, png_bytep data, size_t length) {
   buf_state->data += length;
 }
 
+void* limited_malloc(png_structp, png_alloc_size_t size) {
+  // libpng may allocate large amounts of memory that the fuzzer reports as
+  // an error. In order to silence these errors, make libpng fail when trying
+  // to allocate a large amount. This allocator used to be in the Chromium
+  // version of this fuzzer.
+  // This number is chosen to match the default png_user_chunk_malloc_max.
+  if (size > 8000000)
+    return nullptr;
+
+  return malloc(size);
+}
+
+void default_free(png_structp, png_voidp ptr) {
+  return free(ptr);
+}
+
 static const int kPngHeaderSize = 8;
 
 // Entry point for LibFuzzer.
@@ -118,6 +133,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
     return 0;
   }
 
+  // Use a custom allocator that fails for large allocations to avoid OOM.
+  png_set_mem_fn(png_handler.png_ptr, nullptr, limited_malloc, default_free);
+
   png_set_crc_action(png_handler.png_ptr, PNG_CRC_QUIET_USE, PNG_CRC_QUIET_USE);
 #ifdef PNG_IGNORE_ADLER32
   png_set_option(png_handler.png_ptr, PNG_IGNORE_ADLER32, PNG_OPTION_ON);