netfilter: allow early drop of assured conntracks
If insertion of a new conntrack fails because the table is full, the kernel searches the next buckets of the hash slot where the new connection was supposed to be inserted at for an entry that hasn't seen traffic in reply direction (non-assured), if it finds one, that entry is is dropped and the new connection entry is allocated. Allow the conntrack gc worker to also remove *assured* conntracks if resources are low. Do this by querying the l4 tracker, e.g. tcp connections are now dropped if they are no longer established (e.g. in finwait). This could be refined further, e.g. by adding 'soft' established timeout (i.e., a timeout that is only used once we get close to resource exhaustion). Cc: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: NFlorian Westphal <fw@strlen.de> Acked-by: NJozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
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