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

netfilter: flowtable: hold reference on ct until flow is released

nf_ct_put() releases the ct->ext area inmediately, the rcu typesafe
semantics also allow to refer to the wrong conntrack from the flowtable
datapath. Hold reference on ct until flow is released after rcu grace
period.

Add rcu_barrier() on module exit path, to ensure pending flow entries
are release before module goes away.