third_party/libpng/patches/0002-fuzzeroom.patch

From bd38fe17b88d63245832978286f2fe12c9ed6de7 Mon Sep 17 00:00:00 2001
From: Christopher Thompson <cthomp@chromium.org>
Date: Mon, 12 Nov 2018 09:47:32 -0800
Subject: [PATCH] Add custom malloc with max limit to prevent OOM

This adds the custom malloc/free functions from the old
libpng_read_fuzzer to the upstream fuzzer to prevent clusterfuzz running
into OOM.

Bug: 904054
Change-Id: Ibb824beb191cb5657687c55ee2db8c7783547bad
---

diff --git a/third_party/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc b/third_party/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc
index 3a8ecab..ea27d20 100644
--- a/third_party/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc
+++ b/third_party/libpng/contrib/oss-fuzz/libpng_read_fuzzer.cc
@@ -78,6 +78,21 @@
   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 @@
     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);