[GitHub] [arrow] bkietz commented on a change in pull request #8126: ARROW-9931: [C++] Fix undefined behaviour on invalid IPC input

[GitBox <gi...@apache.org>]

bkietz commented on a change in pull request #8126:
URL: https://github.com/apache/arrow/pull/8126#discussion_r485025998



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File path: cpp/src/arrow/buffer.cc
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@@ -277,13 +277,18 @@ Result<std::unique_ptr<ResizableBuffer>> AllocateResizableBuffer(const int64_t s
 }
 
 Result<std::shared_ptr<Buffer>> AllocateBitmap(int64_t length, MemoryPool* pool) {
-  return AllocateBuffer(BitUtil::BytesForBits(length), pool);
+  ARROW_ASSIGN_OR_RAISE(auto buf, AllocateBuffer(BitUtil::BytesForBits(length), pool));
+  // Zero out any trailing bits
+  if (buf->size() > 0) {
+    buf->mutable_data()[buf->size() - 1] = 0;
+  }
+  return std::move(buf);
 }
 
 Result<std::shared_ptr<Buffer>> AllocateEmptyBitmap(int64_t length, MemoryPool* pool) {
-  ARROW_ASSIGN_OR_RAISE(auto buf, AllocateBitmap(length, pool));
+  ARROW_ASSIGN_OR_RAISE(auto buf, AllocateBuffer(BitUtil::BytesForBits(length), pool));

Review comment:
       It's probably not worth changing that; `AllocateBuffer` zeroes the padding so this doesn't avoid touching the final cache line of this buffer




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