[wasm] Bound the allowed number of locals.

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index 80af396021245b2642b4661a250aa332a8a2f74f..22339a16e900ca5f7be152aa7fcf98fe918a1380 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -661,8 +661,13 @@ class WasmFullDecoder : public WasmDecoder {
     }
     // Decode local declarations, if any.
     uint32_t entries = consume_u32v("local decls count");
+    TRACE("local decls count: %u\n", entries);
     while (entries-- > 0 && pc_ < limit_) {
       uint32_t count = consume_u32v("local count");
+      if (count > 8000000) {

[titzer, 2016/08/25 08:00:26]

Can you introduce a constant in ast-decoder.h and make the test check for counts
around that number?

+        error(pc_ - 1, "local count too large");
+        return;
+      }
       byte code = consume_u8("local type");
       LocalType type;
       switch (code) {