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

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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.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal
2018-12-06 11:50:49 +01:00
committed by Pablo Neira Ayuso
parent 06aa151ad1
commit d535c8a69c
2 changed files with 18 additions and 3 deletions
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16
net/netfilter/nf_conntrack_proto_udp.c
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@@ -100,11 +100,21 @@ static int udp_packet(struct nf_conn *ct,
if (!timeouts)
timeouts = udp_get_timeouts(nf_ct_net(ct));
if (!nf_ct_is_confirmed(ct))
ct->proto.udp.stream_ts = 2 * HZ + jiffies;
/* If we've seen traffic both ways, this is some kind of UDP
stream. Extend timeout. */
* stream. Set Assured.
*/
if (test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
nf_ct_refresh_acct(ct, ctinfo, skb,
timeouts[UDP_CT_REPLIED]);
unsigned long extra = timeouts[UDP_CT_UNREPLIED];
/* Still active after two seconds? Extend timeout. */
if (time_after(jiffies, ct->proto.udp.stream_ts))
extra = timeouts[UDP_CT_REPLIED];
nf_ct_refresh_acct(ct, ctinfo, skb, extra);
/* Also, more likely to be important, and not a probe */
if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
nf_conntrack_event_cache(IPCT_ASSURED, ct);