servo: Merge #18751 - Poison hashtable buffers (from bholley:poison_hashtable); r=Manishearth

This gives us extra defense in depth.

Source-Repo: https://github.com/servo/servo
Source-Revision: 2bbc458c5b2ad44d008cfa57415fe41d1a7ada5e

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : b4c8722fd8a88da9c8d3f21b600085da637e9a9e

servo/components/hashglobe/src/table.rs

@@ -777,13 +777,16 @@ impl<K, V> RawTable<K, V> {
 
 
         // FORK NOTE: Uses alloc shim instead of Heap.alloc
-        let buffer = alloc(size, alignment);
+        let buffer: *mut u8 = alloc(size, alignment);
         
         if buffer.is_null() {
             
             return Err(FailedAllocationError { reason: "out of memory when allocating RawTable" });
         }
 
+        // FORK NOTE: poison the entire buffer rather than leaving it uninitialized.
+        ptr::write_bytes(buffer, 0xe7, size);
+
         let hashes = buffer.offset(hash_offset as isize) as *mut HashUint;
 
         Ok(RawTable {