- Make sure to be able to deal with unaligned snapshot buffers

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
===================================================================
--- runtime/vm/snapshot.cc	(revision 38738)
+++ runtime/vm/snapshot.cc	(working copy)
@@ -136,6 +136,12 @@
          ((1 << RawObject::kWatchedBit) | (1 << RawObject::kMarkBit)));
   ASSERT((kObjectAlignmentMask & kObjectId) == kObjectId);
   const Snapshot* snapshot = reinterpret_cast<const Snapshot*>(raw_memory);
+  // If the raw length is negative or greater than what the local machine can
+  // handle, then signal an error.
+  int64_t snapshot_length = ReadUnaligned(&snapshot->unaligned_length_);
+  if ((snapshot_length < 0) || (snapshot_length > kIntptrMax)) {
+    return NULL;
+  }
   return snapshot;
 }