fix: handle TLS deallocation #324
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Previously, creating a temporary file from a TLS destructor could panic in fastrand (because the thread-local RNG may have been deallocated). Now, we fork the RNG before we create each file, falling back on an RNG with a static seed if the thread-local RNG has been deallocated. Two downsides to this patch: 1. Temporary files created during TLS deallocation will have extremely predictable names until the `getrandom` re-seed kicks in (assuming that feature is enabled). IMO, that's fine; this would panic previously. 2. `getrandom` re-seeding used to re-randomize to the entire per-thread RNG, now it only applies to the per-filename RNG. However, the will still serve its purpose as a mitigation against potential DoS attacks. I also considered managing the thread-local RNG myself instead of relying on fastrand, but that just isn't worth the added code, IMO. Thanks to @stoeckmann for reporting this and explaining the issue to me. I went with this version instead of their version because I needed to keep `tmpname` as a separate function for some tempfile v4 changes. fixes #281
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Sec32fun32
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Feb 20, 2025
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Previously, creating a temporary file from a TLS destructor could panic in fastrand (because the thread-local RNG may have been deallocated).
Now, we fork the RNG before we create each file, falling back on an RNG with a static seed if the thread-local RNG has been deallocated.
Two downsides to this patch:
getrandomre-seed kicks in (assuming that feature is enabled). IMO, that's fine; this would panic previously.getrandomre-seeding used to re-randomize to the entire per-thread RNG, now it only applies to the per-filename RNG. However, the will still serve its purpose as a mitigation against potential DoS attacks.I also considered managing the thread-local RNG myself instead of relying on fastrand, but that just isn't worth the added code, IMO.
Thanks to @stoeckmann for reporting this and explaining the issue to me. I went with this version instead of their version because I needed to keep
tmpnameas a separate function for some tempfile v4 changes.fixes #281
NOTE: there are no tests because I can't actually trigger a crash no matter how I write the test. My test TLS slot is always deallocated first.