CVE-2026-72463: xfrm: Fix dev use-after-free in xfrm async resumption

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

xfrm: Fix dev use-after-free in xfrm async resumption

xfrm async resumption hold skb->dev refcnt until after transportfinish. However, xfrmrcvcb may modify skb->dev to tunnel dev without taking device reference, such as vtircvcb. The subsequent async resumption will decrement the tunnel device's reference count, which lead to uaf of tunnel dev and refcnt leak of orig dev as below:

unregisternetdevice: waiting for vti1 to become free. Usage count = -2

Stash the original skb->dev to fix refcnt imbalance. The new skb->dev set by xfrmrcvcb can race with device teardown. Extend rcu protection over xfrmrcvcb and transportfinish to prevent races.