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gh-142782: Fix use-after-free in the zoneinfo strong cache - #159441
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Comparing a lookup key against a cached key runs the key's __eq__, which can re-enter and call ZoneInfo.clear_cache(), freeing the node being compared; find_in_strong_cache() then dereferenced the freed node. Keep a reference to the node key during the comparison and bump a cache version counter on every mutation, so a lookup that observes a mutation during a comparison returns a miss instead of using a freed node.
tonghuaroot
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StanFromIreland and
pganssle
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October 15, 2026 02:59
maurycy
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Oct 15, 2026
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| klass(Stringy("America/Los_Angeles")) | ||
| klass(Stringy("America/Los_Angeles")) |
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Do we need assertions here?
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| klass(Stringy("America/Los_Angeles")) | |
| klass(Stringy("America/Los_Angeles")) | |
| zone1 = klass(Stringy("America/Los_Angeles")) | |
| zone2 = klass(Stringy("America/Los_Angeles")) | |
| self.assertIsNot(zone2, zone1) | |
| self.assertEqual(str(zone2), "America/Los_Angeles") |
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good point, added the |
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find_in_strong_cache()compares the lookup key against each cached key withPyObject_RichCompareBool(). Astrsubclass whose__eq__callsZoneInfo.clear_cache()frees the node being compared, and the traversal then dereferences the freed node (gh-142782).This keeps a reference to the node key during the comparison, and bumps a
strong_cache_versioncounter on every strong-cache mutation; if the version changes during a comparison, the lookup returns a miss instead of touching a possibly-freed node. This also addresses the false-negative / duplicate concern raised on the issue.Verified under
./configure --with-address-sanitizer: the reproducer and the newtest_strong_cache_reentrant_clearcrash without the fix and are clean with it; the fulltest_zoneinfosuite passes.