netfilter: conntrack: udp: only extend timeout to stream mode after 2s

Currently DNS resolvers that send both A and AAAA queries from same source port can trigger stream mode prematurely, which results in non-early-evictable conntrack entry for three minutes, even though DNS requests are done in a few milliseconds. Add a two second grace period where we continue to use the ordinary 30-second default timeout. Its enough for DNS request/response traffic, even if two request/reply packets are involved. ASSURED is still set, else conntrack (and thus a possible NAT mapping ...) gets zapped too in case conntrack table runs full.

Florian Westphal committed 7 years ago

Commit d535c8a1 parent 06aa1512 files · +18 −3Browse files

Unified · Split

2 files

include/net/netfilter/nf_conntrack.h +5 −0
net/netfilter/nf_conntrack_proto_udp.c +13 −3

include/net/netfilter/nf_conntrack.h+5−0

@@ -27,12 +27,17 @@ · 26 unmodified lines
27	27
28	28	#include <net/netfilter/nf_conntrack_tuple.h>
29	29
	30	+struct nf_ct_udp {
	31	+ unsigned long stream_ts;
	32	+};
	33	+
30	34	/* per conntrack: protocol private data */
31	35	union nf_conntrack_proto {
32	36	/* insert conntrack proto private data here */
33	37	struct nf_ct_dccp dccp;
34	38	struct ip_ct_sctp sctp;
35	39	struct ip_ct_tcp tcp;
	40	+ struct nf_ct_udp udp;
36	41	struct nf_ct_gre gre;
37	42	unsigned int tmpl_padto;
38	43	};

net/netfilter/nf_conntrack_proto_udp.c+13−3

@@ -100,11 +100,21 @@ static int udp_packet(struct nf_conn *ct, · 99 unmodified lines
100	100	if (!timeouts)
101	101	timeouts = udp_get_timeouts(nf_ct_net(ct));
102	102
	103	+ if (!nf_ct_is_confirmed(ct))
	104	+ ct->proto.udp.stream_ts = 2 * HZ + jiffies;
	105	+
103	106	/* If we've seen traffic both ways, this is some kind of UDP
104		− stream. Extend timeout. */
	107	+ * stream. Set Assured.
	108	+ */
105	109	if (test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
106		− nf_ct_refresh_acct(ct, ctinfo, skb,
107		− timeouts[UDP_CT_REPLIED]);
	110	+ unsigned long extra = timeouts[UDP_CT_UNREPLIED];
	111	+
	112	+ /* Still active after two seconds? Extend timeout. */
	113	+ if (time_after(jiffies, ct->proto.udp.stream_ts))
	114	+ extra = timeouts[UDP_CT_REPLIED];
	115	+
	116	+ nf_ct_refresh_acct(ct, ctinfo, skb, extra);
	117	+
108	118	/* Also, more likely to be important, and not a probe */
109	119	if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
110	120	nf_conntrack_event_cache(IPCT_ASSURED, ct);