oss-fuzz: 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: https://bugs.chromium.org/p/chromium/issues/detail?id=904054
Contributed-by: Christopher Thompson <cthomp@chromium.org>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>
diff --git a/contrib/oss-fuzz/libpng_read_fuzzer.cc b/contrib/oss-fuzz/libpng_read_fuzzer.cc
index 7b30550..2064a84 100644
--- a/contrib/oss-fuzz/libpng_read_fuzzer.cc
+++ b/contrib/oss-fuzz/libpng_read_fuzzer.cc
@@ -78,6 +78,22 @@
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 +134,9 @@
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);
