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authorPablo Neira Ayuso <pablo@netfilter.org>2011-02-28 17:59:15 +0100
committerPatrick McHardy <kaber@trash.net>2011-02-28 18:02:33 +0100
commit8a80c79a776d1b1b54895314ffaf53d0c7604c80 (patch)
tree201192d499973c8ca61209962ec1d98624d50ea5 /net/netfilter
parentb552f7e3a9524abcbcdf86f0a99b2be58e55a9c6 (diff)
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netfilter: nf_ct_tcp: fix out of sync scenario while in SYN_RECV
This patch fixes the out of sync scenarios while in SYN_RECV state. Quoting Jozsef, what it happens if we are out of sync if the following: > > b. conntrack entry is outdated, new SYN received > > - (b1) we ignore it but save the initialization data from it > > - (b2) when the reply SYN/ACK receives and it matches the saved data, > > we pick up the new connection This is what it should happen if we are in SYN_RECV state. Initially, the SYN packet hits b1, thus we save data from it. But the SYN/ACK packet is considered a retransmission given that we're in SYN_RECV state. Therefore, we never hit b2 and we don't get in sync. To fix this, we ignore SYN/ACK if we are in SYN_RECV. If the previous packet was a SYN, then we enter the ignore case that get us in sync. This patch helps a lot to conntrackd in stress scenarios (assumming a client that generates lots of small TCP connections). During the failover, consider that the new primary has injected one outdated flow in SYN_RECV state (this is likely to happen if the conntrack event rate is high because the backup will be a bit delayed from the primary). With the current code, if the client starts a new fresh connection that matches the tuple, the SYN packet will be ignored without updating the state tracking, and the SYN+ACK in reply will blocked as it will not pass checkings III or IV (since all state tracking in the original direction is not initialized because of the SYN packet was ignored and the ignore case that get us in sync is not applied). I posted a couple of patches before this one. Changli Gao spotted a simpler way to fix this problem. This patch implements his idea. Cc: Changli Gao <xiaosuo@gmail.com> Cc: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Patrick McHardy <kaber@trash.net>
Diffstat (limited to 'net/netfilter')
-rw-r--r--net/netfilter/nf_conntrack_proto_tcp.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 6f38d0e..37bf943 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -227,11 +227,11 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sCL -> sIV
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
-/*synack*/ { sIV, sSR, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sSR },
+/*synack*/ { sIV, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sIG, sSR },
/*
* sSS -> sSR Standard open.
* sS2 -> sSR Simultaneous open
- * sSR -> sSR Retransmitted SYN/ACK.
+ * sSR -> sIG Retransmitted SYN/ACK, ignore it.
* sES -> sIG Late retransmitted SYN/ACK?
* sFW -> sIG Might be SYN/ACK answering ignored SYN
* sCW -> sIG