Fix reattaching the allocator after compact #3828
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SlabAlloc::detach() sets m_youngest_live_version to 0 and attach() doesn't touch it (as it comes from the lockfile rather than anything it has access to), so compact needs to set m_youngest_live_version after attaching the allocator to the new Realm file. Failing to do this resulted in the first ref translation table being deallocated after the first write transaction even if it was still in use, resulting in a use-after-free for whatever was using it.
jedelbo
approved these changes
Jul 21, 2020
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SlabAlloc::detach() sets m_youngest_live_version to 0 and attach() doesn't touch it (as it comes from the lockfile rather than anything it has access to), so compact needs to set m_youngest_live_version after attaching the allocator to the new Realm file. Failing to do this resulted in the first ref translation table being deallocated after the first write transaction even if it was still in use, resulting in a use-after-free for whatever was using it.
Fixes realm/realm-swift#6652. Fixes realm/realm-swift#6628. Fixes realm/realm-swift#6555.