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gh-159285: Fix crash when copying an empty dict fails with MemoryError - #159286
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methane merged 1 commit intoOct 13, 2026
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…ryError copy_lock_held_untracked() asserted that the new empty dict was not tracked by the GC without checking whether its allocation had failed, so a debug build dereferenced NULL instead of raising MemoryError. This affected dict.copy(), PyDict_Copy() and _PyDict_CopyAsDict(), which type() uses for the class namespace.
christianaurichzm
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methane
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October 13, 2026 02:37
methane
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Oct 13, 2026
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Thanks @christianaurichzm for the PR, and @methane for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15. |
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GH-159287 is a backport of this pull request to the 3.15 branch. |
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GH-159286) copy_lock_held_untracked() asserted that the new empty dict was not tracked by the GC without checking whether its allocation had failed, so a debug build dereferenced NULL instead of raising MemoryError. This affected dict.copy(), PyDict_Copy() and _PyDict_CopyAsDict(), which type() uses for the class namespace. (cherry picked from commit f9132f1) Co-authored-by: Christian Aurich Zanettini Martins <christian.aurichzm@gmail.com>
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Fixes #159285
copy_lock_held_untracked()handles the empty-dict case by allocating a new dict and then asserting!_PyObject_GC_IS_TRACKED(d). When the allocation fails,disNULLand the assertion dereferences it, so a debug build segfaults instead of raisingMemoryError. This is reachable fromdict.copy(),PyDict_Copy()and_PyDict_CopyAsDict(), whichtype()uses for the class namespace.This change lets the assertion accept
NULL. Release builds are unchanged, since they already returnedNULLwithMemoryErrorset.Verification
test_dictsegfaults an unpatched debug build and passes with the fix, also with-R 3:3.test_dict,test_capi.test_dict,test_class,test_descr,test_typesandtest_gcpass on a debug build.