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netfilter: nf_ct_tcp: TCP simultaneous open support
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The patch below adds supporting TCP simultaneous open to conntrack. The
unused LISTEN state is replaced by a new state (SYN_SENT2) denoting the
second SYN sent from the reply direction in the new case. The state table
is updated and the function tcp_in_window is modified to handle
simultaneous open.

The functionality can fairly easily be tested by socat. A sample tcpdump
recording

23:21:34.244733 IP (tos 0x0, ttl 64, id 49224, offset 0, flags [DF], proto TCP (6), length 60) 192.168.0.254.2020 > 192.168.0.1.2020: S, cksum 0xe75f (correct), 3383710133:3383710133(0) win 5840 <mss 1460,sackOK,timestamp 173445629 0,nop,wscale 7>
23:21:34.244783 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 40) 192.168.0.1.2020 > 192.168.0.254.2020: R, cksum 0x0253 (correct), 0:0(0) ack 3383710134 win 0
23:21:36.038680 IP (tos 0x0, ttl 64, id 28092, offset 0, flags [DF], proto TCP (6), length 60) 192.168.0.1.2020 > 192.168.0.254.2020: S, cksum 0x704b (correct), 2634546729:2634546729(0) win 5840 <mss 1460,sackOK,timestamp 824213 0,nop,wscale 1>
23:21:36.038777 IP (tos 0x0, ttl 64, id 49225, offset 0, flags [DF], proto TCP (6), length 60) 192.168.0.254.2020 > 192.168.0.1.2020: S, cksum 0xb179 (correct), 3383710133:3383710133(0) ack 2634546730 win 5840 <mss 1460,sackOK,timestamp 173447423 824213,nop,wscale 7>
23:21:36.038847 IP (tos 0x0, ttl 64, id 28093, offset 0, flags [DF], proto TCP (6), length 52) 192.168.0.1.2020 > 192.168.0.254.2020: ., cksum 0xebad (correct), ack 3383710134 win 2920 <nop,nop,timestamp 824213 173447423>

and the corresponding netlink events:

    [NEW] tcp      6 120 SYN_SENT src=192.168.0.254 dst=192.168.0.1 sport=2020 dport=2020 [UNREPLIED] src=192.168.0.1 dst=192.168.0.254 sport=2020 dport=2020
 [UPDATE] tcp      6 120 LISTEN src=192.168.0.254 dst=192.168.0.1 sport=2020 dport=2020 src=192.168.0.1 dst=192.168.0.254 sport=2020 dport=2020
 [UPDATE] tcp      6 60 SYN_RECV src=192.168.0.254 dst=192.168.0.1 sport=2020 dport=2020 src=192.168.0.1 dst=192.168.0.254 sport=2020 dport=2020
 [UPDATE] tcp      6 432000 ESTABLISHED src=192.168.0.254 dst=192.168.0.1 sport=2020 dport=2020 src=192.168.0.1 dst=192.168.0.254 sport=2020 dport=2020 [ASSURED]

The RST packet was dropped in the raw table, thus it did not reach
conntrack.  nfnetlink_conntrack is unpatched so it shows the new SYN_SENT2
state as the old unused LISTEN.

With TCP simultaneous open support we satisfy REQ-2 in RFC 5382  ;-) .

Additional minor correction in this patch is that in order to catch
uninitialized reply directions, "td_maxwin == 0" is used instead of
"td_end == 0" because the former can't be true except in uninitialized
state while td_end may accidentally be equal to zero in the mid of a
connection.

Signed-off-by: Jozsef Kadlecsik <[email protected]>
Signed-off-by: Patrick McHardy <[email protected]>
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Jozsef Kadlecsik authored and kaber committed Jun 2, 2009
1 parent 8cc848f commit 874ab92
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Showing 2 changed files with 63 additions and 38 deletions.
3 changes: 2 additions & 1 deletion include/linux/netfilter/nf_conntrack_tcp.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ enum tcp_conntrack {
TCP_CONNTRACK_LAST_ACK,
TCP_CONNTRACK_TIME_WAIT,
TCP_CONNTRACK_CLOSE,
TCP_CONNTRACK_LISTEN,
TCP_CONNTRACK_LISTEN, /* obsolete */
#define TCP_CONNTRACK_SYN_SENT2 TCP_CONNTRACK_LISTEN
TCP_CONNTRACK_MAX,
TCP_CONNTRACK_IGNORE
};
Expand Down
98 changes: 61 additions & 37 deletions net/netfilter/nf_conntrack_proto_tcp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ static const char *const tcp_conntrack_names[] = {
"LAST_ACK",
"TIME_WAIT",
"CLOSE",
"LISTEN"
"SYN_SENT2",
};

#define SECS * HZ
Expand All @@ -82,6 +82,7 @@ static unsigned int tcp_timeouts[TCP_CONNTRACK_MAX] __read_mostly = {
[TCP_CONNTRACK_LAST_ACK] = 30 SECS,
[TCP_CONNTRACK_TIME_WAIT] = 2 MINS,
[TCP_CONNTRACK_CLOSE] = 10 SECS,
[TCP_CONNTRACK_SYN_SENT2] = 2 MINS,
};

#define sNO TCP_CONNTRACK_NONE
Expand All @@ -93,7 +94,7 @@ static unsigned int tcp_timeouts[TCP_CONNTRACK_MAX] __read_mostly = {
#define sLA TCP_CONNTRACK_LAST_ACK
#define sTW TCP_CONNTRACK_TIME_WAIT
#define sCL TCP_CONNTRACK_CLOSE
#define sLI TCP_CONNTRACK_LISTEN
#define sS2 TCP_CONNTRACK_SYN_SENT2
#define sIV TCP_CONNTRACK_MAX
#define sIG TCP_CONNTRACK_IGNORE

Expand Down Expand Up @@ -123,6 +124,7 @@ enum tcp_bit_set {
*
* NONE: initial state
* SYN_SENT: SYN-only packet seen
* SYN_SENT2: SYN-only packet seen from reply dir, simultaneous open
* SYN_RECV: SYN-ACK packet seen
* ESTABLISHED: ACK packet seen
* FIN_WAIT: FIN packet seen
Expand All @@ -131,26 +133,24 @@ enum tcp_bit_set {
* TIME_WAIT: last ACK seen
* CLOSE: closed connection (RST)
*
* LISTEN state is not used.
*
* Packets marked as IGNORED (sIG):
* if they may be either invalid or valid
* and the receiver may send back a connection
* closing RST or a SYN/ACK.
*
* Packets marked as INVALID (sIV):
* if they are invalid
* or we do not support the request (simultaneous open)
* if we regard them as truly invalid packets
*/
static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
{
/* ORIGINAL */
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*syn*/ { sSS, sSS, sIG, sIG, sIG, sIG, sIG, sSS, sSS, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*syn*/ { sSS, sSS, sIG, sIG, sIG, sIG, sIG, sSS, sSS, sS2 },
/*
* sNO -> sSS Initialize a new connection
* sSS -> sSS Retransmitted SYN
* sSR -> sIG Late retransmitted SYN?
* sS2 -> sS2 Late retransmitted SYN
* sSR -> sIG
* sES -> sIG Error: SYNs in window outside the SYN_SENT state
* are errors. Receiver will reply with RST
* and close the connection.
Expand All @@ -161,22 +161,30 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sSS Reopened connection (RFC 1122).
* sCL -> sSS
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*synack*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*synack*/ { sIV, sIV, sIG, sIG, sIG, sIG, sIG, sIG, sIG, sSR },
/*
* A SYN/ACK from the client is always invalid:
* - either it tries to set up a simultaneous open, which is
* not supported;
* - or the firewall has just been inserted between the two hosts
* during the session set-up. The SYN will be retransmitted
* by the true client (or it'll time out).
* sNO -> sIV Too late and no reason to do anything
* sSS -> sIV Client can't send SYN and then SYN/ACK
* sS2 -> sSR SYN/ACK sent to SYN2 in simultaneous open
* sSR -> sIG
* sES -> sIG Error: SYNs in window outside the SYN_SENT state
* are errors. Receiver will reply with RST
* and close the connection.
* Or we are not in sync and hold a dead connection.
* sFW -> sIG
* sCW -> sIG
* sLA -> sIG
* sTW -> sIG
* sCL -> sIG
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*fin*/ { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
/*
* sNO -> sIV Too late and no reason to do anything...
* sSS -> sIV Client migth not send FIN in this state:
* we enforce waiting for a SYN/ACK reply first.
* sS2 -> sIV
* sSR -> sFW Close started.
* sES -> sFW
* sFW -> sLA FIN seen in both directions, waiting for
Expand All @@ -187,11 +195,12 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sTW
* sCL -> sCL
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*ack*/ { sES, sIV, sES, sES, sCW, sCW, sTW, sTW, sCL, sIV },
/*
* sNO -> sES Assumed.
* sSS -> sIV ACK is invalid: we haven't seen a SYN/ACK yet.
* sS2 -> sIV
* sSR -> sES Established state is reached.
* sES -> sES :-)
* sFW -> sCW Normal close request answered by ACK.
Expand All @@ -200,29 +209,31 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sTW Retransmitted last ACK. Remain in the same state.
* sCL -> sCL
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*rst*/ { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*rst*/ { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL },
/*none*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
},
{
/* REPLY */
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*syn*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*syn*/ { sIV, sS2, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sS2 },
/*
* sNO -> sIV Never reached.
* sSS -> sIV Simultaneous open, not supported
* sSR -> sIV Simultaneous open, not supported.
* sES -> sIV Server may not initiate a connection.
* sSS -> sS2 Simultaneous open
* sS2 -> sS2 Retransmitted simultaneous SYN
* sSR -> sIV Invalid SYN packets sent by the server
* sES -> sIV
* sFW -> sIV
* sCW -> sIV
* sLA -> sIV
* sTW -> sIV Reopened connection, but server may not do it.
* sCL -> sIV
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*synack*/ { sIV, sSR, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*synack*/ { sIV, sSR, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sSR },
/*
* sSS -> sSR Standard open.
* sS2 -> sSR Simultaneous open
* sSR -> sSR Retransmitted SYN/ACK.
* sES -> sIG Late retransmitted SYN/ACK?
* sFW -> sIG Might be SYN/ACK answering ignored SYN
Expand All @@ -231,10 +242,11 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sIG
* sCL -> sIG
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*fin*/ { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
/*
* sSS -> sIV Server might not send FIN in this state.
* sS2 -> sIV
* sSR -> sFW Close started.
* sES -> sFW
* sFW -> sLA FIN seen in both directions.
Expand All @@ -243,10 +255,11 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sTW
* sCL -> sCL
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*ack*/ { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*ack*/ { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIG },
/*
* sSS -> sIG Might be a half-open connection.
* sS2 -> sIG
* sSR -> sSR Might answer late resent SYN.
* sES -> sES :-)
* sFW -> sCW Normal close request answered by ACK.
Expand All @@ -255,8 +268,8 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
* sTW -> sTW Retransmitted last ACK.
* sCL -> sCL
*/
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI */
/*rst*/ { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
/* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */
/*rst*/ { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL },
/*none*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
}
};
Expand Down Expand Up @@ -521,13 +534,14 @@ static bool tcp_in_window(const struct nf_conn *ct,
receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
receiver->td_scale);

if (sender->td_end == 0) {
if (sender->td_maxwin == 0) {
/*
* Initialize sender data.
*/
if (tcph->syn && tcph->ack) {
if (tcph->syn) {
/*
* Outgoing SYN-ACK in reply to a SYN.
* SYN-ACK in reply to a SYN
* or SYN from reply direction in simultaneous open.
*/
sender->td_end =
sender->td_maxend = end;
Expand All @@ -543,6 +557,9 @@ static bool tcp_in_window(const struct nf_conn *ct,
&& receiver->flags & IP_CT_TCP_FLAG_WINDOW_SCALE))
sender->td_scale =
receiver->td_scale = 0;
if (!tcph->ack)
/* Simultaneous open */
return true;
} else {
/*
* We are in the middle of a connection,
Expand Down Expand Up @@ -1068,7 +1085,7 @@ static bool tcp_new(struct nf_conn *ct, const struct sk_buff *skb,

ct->proto.tcp.seen[1].td_end = 0;
ct->proto.tcp.seen[1].td_maxend = 0;
ct->proto.tcp.seen[1].td_maxwin = 1;
ct->proto.tcp.seen[1].td_maxwin = 0;
ct->proto.tcp.seen[1].td_scale = 0;

/* tcp_packet will set them */
Expand Down Expand Up @@ -1309,6 +1326,13 @@ static struct ctl_table tcp_compat_sysctl_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "ip_conntrack_tcp_timeout_syn_sent2",
.data = &tcp_timeouts[TCP_CONNTRACK_SYN_SENT2],
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "ip_conntrack_tcp_timeout_syn_recv",
.data = &tcp_timeouts[TCP_CONNTRACK_SYN_RECV],
Expand Down

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