[release/10.0] Fix TOCTOU race in AppDomain::LoadAssembly fast-path#125424
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JulieLeeMSFT merged 1 commit intorelease/10.0from Mar 11, 2026
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[release/10.0] Fix TOCTOU race in AppDomain::LoadAssembly fast-path#125424JulieLeeMSFT merged 1 commit intorelease/10.0from
JulieLeeMSFT merged 1 commit intorelease/10.0from
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PR #120515 deferred Assembly creation (lazy init), making FileLoadLock::m_pAssembly mutable. The fast-path in LoadAssembly cached pAssembly before checking GetLoadLevel(), so a thread could read nullptr, get preempted while another thread completed the load, then pass the level check and dereference the stale nullptr. Re-read pAssembly from the FileLoadLock inside the fast-path block after the level check passes, ensuring we use the pointer that corresponds to the observed load level. Co-authored-by: Copilot <[email protected]>
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Tagging subscribers to this area: @agocke |
AaronRobinsonMSFT
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/ba-g The test failure is a known issue. |
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Backport of #125408 to release/10.0
/cc @AaronRobinsonMSFT
Customer Impact
The reproduction rate in a real application environment is extremely low (< 1/100,000) as it requires simultaneous EOF on stdout/stderr, an unloaded target assembly, and exact OS thread preemption. This is a reliability issue tht impacted a high value enterprise customer and can impact other users.
Regression
Yes in PR #120515.
Testing
The change here is an obvious TOCTOU issue. The source was updated in a clearer way to avoid creating locals that are populated long before use.
Risk
Low. The source change is narrowing the use of a local behind a lock in a manner that is more local to use. This reflects better engineering practices and can easily be audited for correctness.