← WebKit — 2026-W36
7224709bf0747d1cb8f7d52e65cc7900e91fdb75 [threaded-animations] cross-thread UAF in UIProcess via unguarded static TinyLRUCache in AcceleratedEffect polygon path cache
severity medium
class Race
confidence 0.65
signal score 7.3
Source/WebCore/platform
patch-now
Primitive: Shared TinyLRUCache mutated/returned-by-reference across main and scrolling threads
Triage note: The cachedAcceleratedEffect*Path helpers now take a static Lock and return the Path by value instead of const-ref, with comments noting concurrent access from the main run loop and ScrollingThread via RemoteLayerTreeEventDispatcher::updateAnimations. Fixes a data race and a dangling reference to an entry another thread can evict.
Triage note: The cachedAcceleratedEffect*Path helpers now take a static Lock and return the Path by value instead of const-ref, with comments noting concurrent access from the main run loop and ScrollingThread via RemoteLayerTreeEventDispatcher::updateAnimations. Fixes a data race and a dangling reference to an entry another thread can evict.
Structural signals: msg_strong (+3.0), msg_medium (+2.0), msg_soft (+1.0), surgical (+1.3)
Commit message
[threaded-animations] cross-thread UAF in UIProcess via unguarded static TinyLRUCache in AcceleratedEffect polygon path cache
https://bugs.webkit.org/show_bug.cgi?id=317919
rdar://180233994
Reviewed by Chris Dumez.
Values held by AcceleratedEffectValues may be accessed both from the main thread
and the scrolling thread on macOS.
Meanwhile, the `cachedAcceleratedEffectXXXPath()` family of functions use a process-global
`static NeverDestroyed<TinyLRUCache<..., WebCore::Path, 4, ...>>` with no synchronization
and return a `const Path&` directly into a cache slot. TinyLRUCache::get() move-assigns
slots whose `Path` value wraps `DataRef<PathImpl>`, a concurrent move-assignment
tears the non-atomic pointer read/swap in `Ref::operator=(Ref&&)` and produces
a stale refcounted pointer that is then deref'd, yielding a use-after-free
or double-free of `PathImpl`.
We now guard each cache with a static Lock and return Path by value so the cache
slot is copied out while the lock is held. `PathImpl` is `ThreadSafeRefCounted`
so the by-value copy is just an atomic refcount bump. This matches the existing
pattern used by `cachedCGColor()` and `UTIFromMIMEType()` for concurrently-accessed
static `TinyLRUCache` instances.
This fix was suggested by an LLM during bug analysis, I validated its approach.
Test: webanimations/threaded-animations/offset-path-shape-cache-thread-safety-crash.html
* LayoutTests/webanimations/threaded-animations/offset-path-shape-cache-thread-safety-crash-expected.txt: Added.
* LayoutTests/webanimations/threaded-animations/offset-path-shape-cache-thread-safety-crash.html: Added.
* LayoutTests/webanimations/threaded-animations/resources/offset-path-shape-cache-thread-safety-popup.html: Added.
* Source/WebCore/platform/animation/values/shapes/AcceleratedEffectCircleFunction.cpp:
(WebCore::cachedAcceleratedEffectCirclePath):
* Source/WebCore/platform/animation/values/shapes/AcceleratedEffectEllipseFunction.cpp:
(WebCore::cachedAcceleratedEffectEllipsePath):
* Source/WebCore/platform/animation/values/shapes/AcceleratedEffectInsetFunction.cpp:
(WebCore::cachedRoundedInsetPath):
* Source/WebCore/platform/animation/values/shapes/AcceleratedEffectPathFunction.cpp:
(WebCore::cachedAcceleratedEffectTransformedByteStreamPath):
* Source/WebCore/platform/animation/values/shapes/AcceleratedEffectPolygonFunction.cpp:
(WebCore::cachedAcceleratedEffectPolygonPath):
Originally-landed-as: [email protected] (e4960726c71e). rdar://185368955
Canonical link: https://commits.webkit.org/320360@main
Before / after
Loading diff…
On This Page