[PATCH AUTOSEL 6.1 15/29] netfilter: conntrack: check SCTP_CID_SHUTDOWN_ACK for vtag setting in sctp_new

Sasha Levin
2024-02-07T21:25:35Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit 6e348067ee4bc5905e35faa3a8fafa91c9124bc7 ]

The annotation says in sctp_new(): "If it is a shutdown ack OOTB packet, we
expect a return shutdown complete, otherwise an ABORT Sec 8.4 (5) and (8)".
However, it does not check SCTP_CID_SHUTDOWN_ACK before setting vtag[REPLY]
in the conntrack entry(ct).

Because of that, if the ct in Router disappears for some reason in [1]
with the packet sequence like below:

Client > Server: sctp (1) [INIT] [init tag: 3201533963]
Server > Client: sctp (1) [INIT ACK] [init tag: 972498433]
Client > Server: sctp (1) [COOKIE ECHO]
Server > Client: sctp (1) [COOKIE ACK]
Client > Server: sctp (1) [DATA] (B)(E) [TSN: 3075057809]
Server > Client: sctp (1) [SACK] [cum ack 3075057809]
Server > Client: sctp (1) [HB REQ]
(the ct in Router disappears somehow) <-------- [1]
Client > Server: sctp (1) [HB ACK]
Client > Server: sctp (1) [DATA] (B)(E) [TSN: 3075057810]
Client > Server: sctp (1) [DATA] (B)(E) [TSN: 3075057810]
Client > Server: sctp (1) [HB REQ]
Client > Server: sctp (1) [DATA] (B)(E) [TSN: 3075057810]
Client > Server: sctp (1) [HB REQ]
Client > Server: sctp (1) [ABORT]

when processing HB ACK packet in Router it calls sctp_new() to initialize
the new ct with vtag[REPLY] set to HB_ACK packet's vtag.

Later when sending DATA from Client, all the SACKs from Server will get
dropped in Router, as the SACK packet's vtag does not match vtag[REPLY]
in the ct. The worst thing is the vtag in this ct will never get fixed
by the upcoming packets from Server.

This patch fixes it by checking SCTP_CID_SHUTDOWN_ACK before setting
vtag[REPLY] in the ct in sctp_new() as the annotation says. With this
fix, it will leave vtag[REPLY] in ct to 0 in the case above, and the
next HB REQ/ACK from Server is able to fix the vtag as its value is 0
in nf_conntrack_sctp_packet().

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_conntrack_proto_sctp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c
index c94a9971d790..7ffd698497f2 100644
--- a/net/netfilter/nf_conntrack_proto_sctp.c
+++ b/net/netfilter/nf_conntrack_proto_sctp.c
@@ -299,7 +299,7 @@ sctp_new(struct nf_conn *ct, const struct sk_buff *skb,
pr_debug("Setting vtag %x for secondary conntrack\n",
sh->vtag);
ct->proto.sctp.vtag[IP_CT_DIR_ORIGINAL] = sh->vtag;
- } else {
+ } else if (sch->type == SCTP_CID_SHUTDOWN_ACK) {
/* If it is a shutdown ack OOTB packet, we expect a return
shutdown complete, otherwise an ABORT Sec 8.4 (5) and (8) */
pr_debug("Setting vtag %x for new conn OOTB\n",
--
2.43.0