netfilter: let reset rules clean out conntrack entries

iptables/nftables support responding to tcp packets with tcp resets.

The generated tcp reset packet passes through both output and postrouting
netfilter hooks, but conntrack will never see them because the generated
skb has its ->nfct pointer copied over from the packet that triggered the
reset rule.

If the reset rule is used for established connections, this
may result in the conntrack entry to be around for a very long
time (default timeout is 5 days).

One way to avoid this would be to not copy the nf_conn pointer
so that the rest packet passes through conntrack too.

Problem is that output rules might not have the same conntrack
zone setup as the prerouting ones, so its possible that the
reset skb won't find the correct entry.  Generating a template
entry for the skb seems error prone as well.

Add an explicit "closing" function that switches a confirmed
conntrack entry to closed state and wire this up for tcp.

If the entry isn't confirmed, no action is needed because
the conntrack entry will never be committed to the table.

Reported-by: Russel King <linux@armlinux.org.uk>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index 6a2019aaa4644..3dbf947285be2 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -126,6 +126,12 @@ struct nf_conn {
 };
 
 static inline struct nf_conn *
+nf_ct_to_nf_conn(const struct nf_conntrack *nfct)
+{
+	return container_of(nfct, struct nf_conn, ct_general);
+}
+
+static inline struct nf_conn *
 nf_ct_tuplehash_to_ctrack(const struct nf_conntrack_tuple_hash *hash)
 {
 	return container_of(hash, struct nf_conn,
@@ -175,6 +181,8 @@ nf_ct_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
 
 void nf_ct_destroy(struct nf_conntrack *nfct);
 
+void nf_conntrack_tcp_set_closing(struct nf_conn *ct);
+
 /* decrement reference count on a conntrack */
 static inline void nf_ct_put(struct nf_conn *ct)
 {