gh-143228: Fix UAF in perf trampoline during finalization #143233
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pablogsal
requested review from
ZeroIntensity and
ericsnowcurrently
as code owners
When toggling perf trampoline while threads are running, or during interpreter finalization with daemon threads active, a use-after-free occurs. The munmap call in free_code_arenas releases executable memory while other threads may still be executing within trampolines or unwinding through them, causing SIGSEGV or SystemError. The fix uses reference counting with a code watcher. Each code object that receives a trampoline increments a refcount. When code objects are destroyed, the watcher decrements the refcount and frees arenas only when it reaches zero. This ensures trampolines are never freed while any code object could still reference them.
pablogsal
added
needs backport to 3.13
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When toggling perf trampoline while threads are running, or during
interpreter finalization with daemon threads active, a use-after-free
occurs. The munmap call in free_code_arenas releases executable memory
while other threads may still be executing within trampolines or
unwinding through them, causing SIGSEGV or SystemError.
The fix uses reference counting with a code watcher. Each code object
that receives a trampoline increments a refcount. When code objects are
destroyed, the watcher decrements the refcount and frees arenas only
when it reaches zero. This ensures trampolines are never freed while
any code object could still reference them.