netfilter: ctnetlink: disable helper autoassign
When userspace, e.g. conntrackd, inserts an entry with a specified helper, its possible that the helper is lost immediately after its added: ctnetlink_create_conntrack -> nf_ct_helper_ext_add + assign helper -> ctnetlink_setup_nat -> ctnetlink_parse_nat_setup -> parse_nat_setup -> nfnetlink_parse_nat_setup -> nf_nat_setup_info -> nf_conntrack_alter_reply -> __nf_ct_try_assign_helper ... and __nf_ct_try_assign_helper will zero the helper again. Set IPS_HELPER bit to bypass auto-assign logic, its unwanted, just like when helper is assigned via ruleset. Dropped old 'not strictly necessary' comment, it referred to use of rcu_assign_pointer() before it got replaced by RCU_INIT_POINTER(). NB: Fixes tag intentionally incorrect, this extends the referenced commit, but this change won't build without IPS_HELPER introduced there. Fixes: 6714cf54 ("netfilter: nf_conntrack: fix explicit helper attachment and NAT") Reported-by: Pham Thanh Tuyen <phamtyn@gmail.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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