Limit Mojo messages recursion depth

mojo/public/cpp/bindings/lib/validation_context.h

Index: mojo/public/cpp/bindings/lib/validation_context.h
diff --git a/mojo/public/cpp/bindings/lib/validation_context.h b/mojo/public/cpp/bindings/lib/validation_context.h
index 55d083cffe97691d6cc87a64adc447b63e077c7f..ea73df95e4f323edb549b25023f9117924b0b0ba 100644
--- a/mojo/public/cpp/bindings/lib/validation_context.h
+++ b/mojo/public/cpp/bindings/lib/validation_context.h
@@ -12,6 +12,8 @@
 #include "base/strings/string_piece.h"
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 
+static const int kMaxRecursionDepth = 100;

[dcheng, 2016/09/06 21:37:03]

I'd suggest a more conservative limit. Maybe 50, since that's what the current
ParamTraits for base::Value limits it to.

[tibell, 2016/09/07 05:41:20]

I took this from the old IPC limit at
https://cs.chromium.org/chromium/src/ipc/ipc_message_utils.cc?q=kMaxRecursion...
in order to not have it get in the way of some conversion.

+
 namespace mojo {
 
 class Message;
@@ -33,7 +35,8 @@ class ValidationContext {
                     size_t data_num_bytes,
                     size_t num_handles,
                     Message* message = nullptr,
-                    const base::StringPiece& description = "");
+                    const base::StringPiece& description = "",
+                    int stack_depth = 0);
 
   ~ValidationContext();
 
@@ -81,6 +84,31 @@ class ValidationContext {
     return InternalIsValidRange(begin, end);
   }
 
+  // This object should be created on the stack once every time we recurse down
+  // into a subfield during validation to make sure we don't recurse too deep
+  // and blow the stack.
+  class ScopedDepthTracker {
+   public:
+    // |ctx| must outlive this object.
+    ScopedDepthTracker(ValidationContext* ctx) : ctx_(ctx) {

[dcheng, 2016/09/06 21:37:02]

Nit: explicit

[tibell, 2016/09/07 05:41:20]

Done.

+      ++ctx_->stack_depth_;
+    }
+
+    ~ScopedDepthTracker() {
+      --ctx_->stack_depth_;
+    }
+
+   private:
+    ValidationContext* ctx_;
+
+    DISALLOW_COPY_AND_ASSIGN(ScopedDepthTracker);

[dcheng, 2016/09/06 21:37:02]

Nit: include base/compiler_specific.h

[tibell, 2016/09/07 05:41:20]

Done.

+  };
+
+  // Returns true if the recursion depth limit has been reached.
+  bool ExceedsMaxDepth() WARN_UNUSED_RESULT {
+    return stack_depth_ > kMaxRecursionDepth;
+  }
+
   Message* message() const { return message_; }
   const base::StringPiece& description() const { return description_; }
 
@@ -100,6 +128,8 @@ class ValidationContext {
   uint32_t handle_begin_;
   uint32_t handle_end_;
 
+  int stack_depth_;
+
   DISALLOW_COPY_AND_ASSIGN(ValidationContext);
 };