Hi Patrick,
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.
---
include/linux/netfilter/nf_conntrack_tcp.h | 2 +-
net/netfilter/nf_conntrack_proto_tcp.c | 97 +++++++++++++++++-----------
2 files changed, 61 insertions(+), 38 deletions(-)
diff --git a/include/linux/netfilter/nf_conntrack_tcp.h b/include/linux/netfilter/nf_conntrack_tcp.h
index b2f384d..05d17c7 100644
--- a/include/linux/netfilter/nf_conntrack_tcp.h
+++ b/include/linux/netfilter/nf_conntrack_tcp.h
@@ -15,7 +15,7 @@ enum tcp_conntrack {
TCP_CONNTRACK_LAST_ACK,
TCP_CONNTRACK_TIME_WAIT,
TCP_CONNTRACK_CLOSE,
- TCP_CONNTRACK_LISTEN,
+ TCP_CONNTRACK_SYN_SENT2,
TCP_CONNTRACK_MAX,
TCP_CONNTRACK_IGNORE
};
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 97a6e93..ba96d12 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -59,7 +59,7 @@ static const char *const tcp_conntrack_names[] = {
"LAST_ACK",
"TIME_WAIT",
"CLOSE",
- "LISTEN"
+ "SYN_SENT2",
};
#define SECS * HZ
@@ -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
@@ -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
@@ -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
@@ -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.
@@ -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
@@ -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.
@@ -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
@@ -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.
@@ -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.
@@ -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 }
}
};
@@ -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;
@@ -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,
@@ -1086,7 +1103,7 @@ 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 */
@@ -1327,6 +1344,12 @@ 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],
--
1.5.4.3
Best regards,
Jozsef
-
E-mail : kadlec@xxxxxxxxxxxxxxxxx, kadlec@xxxxxxxxxxxx
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : KFKI Research Institute for Particle and Nuclear Physics
H-1525 Budapest 114, POB. 49, Hungary
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