On Wed, 2019-02-27 at 17:50 -0800, Cong Wang wrote: > > + if (oldchain) > > + tcf_chain_put_by_act(oldchain); > > Do we need to respect RCU grace period here?
if I well understand the question, you are worried about tcf_action_goto_chain_exec(), that can dereference 'oldchain' while we are overwriting the action. A call to tcf_chain_put_by_act(oldchain) would decrease refcounts and eventually call kfree(oldchain). But this would result in a use-after-free only in case the chain has only refcount held by 1 action (the one we are overwriting), and 0 filters: is this a condition where packets can go through this action's data plane? In every other case, the chain is refcounted at least by 1 filter. So, normally the worst case would be a packet routed on the wrong chain, which is not much different than what already happens now when a valid 'goto chain' rule is overwritten with another valid 'goto chain' rule. Am I missing something? thank you in advance, -- davide
