Linux kernel Rust Binder: dropped node refcount updates on thread exit

In the Linux kernel, the following vulnerability has been resolved:

rust_binder: reschedule node refcount update on thread exit

When a thread exits via BINDER_THREAD_EXIT, its pending work items are cancelled. If a thread exits while holding a pending node refcount increment (e.g. pushed as deferred work to that thread), the refcount increment was previously dropped because Node::cancel() and NodeWrapper::cancel() were no-ops.

Dropping the refcount update leaves the node's delivery state and count state desynchronized, and userspace will not receive the notification, which can cause the node to never be freed from the process's nodes tree when all external references are dropped.

Fix this by implementing DeliverToRead::cancel() for Node and NodeWrapper to move the pending refcount update to the process's work queue on thread exit so another thread can deliver it to userspace.