[compiler-rt] [scudo] Update header without read-modify-write operation (PR #66955)

[Christopher Ferris via llvm-commits]

cferris1000 wrote:

Yeah, we agree there is a small loss of security. We are trying to think of another method to detect this error that might not give as much information, but prevent the error from occurring. For example, if this happened then it's likely the same allocation winds up twice in a list, and maybe there is a way we can modify the header when doing an allocation that prevents the same allocation from being used twice. If you've got any ideas along that line, let us know.

Our thinking is that as a pure bug, the chance of this happening is low. If you trigger this problem, you will likely trigger a normal double free so the chance of only every seeing the multiple threads double freeing at the same time is low. Thus you will still see the double free error.

https://github.com/llvm/llvm-project/pull/66955