[PATCH net v2] selftests: netfilter: conntrack_sctp_collision.sh: Introduce SCTP INIT collision test

[PATCH net v2] selftests: netfilter: conntrack_sctp_collision.sh: Introduce SCTP INIT collision test

[Yi Chen]

The existing test covered a scenario where a delayed INIT_ACK chunk
updates the vtag in conntrack after the association has already been
established.

A similar issue can occur with a delayed SCTP INIT chunk.

Add a new simultaneous-open test case where the client's INIT is
delayed, allowing conntrack to establish the association based on
the server-initiated handshake.

When the stale INIT arrives later, it may get recorded and cause a
following INIT_ACK from the peer to be accepted instead of dropped.
This INIT_ACK overwrites the vtag in conntrack, causing subsequent
SCTP DATA chunks to be considered as invalid and then dropped by
nft rules matching on ct state invalid.

This test verifies such stale INIT chunks do not cause problems.

Signed-off-by: Yi Chen <yiche.cy@gmail.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
---
v1 -> v2:
- Simplify conf_delay() by passing arguments.
- Avoid calling exit() inside the function.
- Enable nft log by setting net.netfilter.nf_log_all_netns=1.
- Add a description for the "ct invalid drop" rule match.
---
 .../net/netfilter/conntrack_sctp_collision.sh | 85 ++++++++++++++-----
 1 file changed, 63 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/net/netfilter/conntrack_sctp_collision.sh b/tools/testing/selftests/net/netfilter/conntrack_sctp_collision.sh
index d860f7d9744b..31823050391e 100755
--- a/tools/testing/selftests/net/netfilter/conntrack_sctp_collision.sh
+++ b/tools/testing/selftests/net/netfilter/conntrack_sctp_collision.sh
@@ -2,18 +2,32 @@
 # SPDX-License-Identifier: GPL-2.0
 #
 # Testing For SCTP COLLISION SCENARIO as Below:
-#
+# 1. Stale INIT_ACK capture:
 #   14:35:47.655279 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [INIT] [init tag: 2017837359]
 #   14:35:48.353250 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [INIT] [init tag: 1187206187]
 #   14:35:48.353275 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [INIT ACK] [init tag: 2017837359]
 #   14:35:48.353283 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [COOKIE ECHO]
 #   14:35:48.353977 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [COOKIE ACK]
 #   14:35:48.855335 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [INIT ACK] [init tag: 164579970]
+#   (Delayed)
+#
+# 2. Stale INIT capture:
+#   14:35:48.353250 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [INIT] [init tag: 1187206187]
+#   14:35:48.353275 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [INIT ACK] [init tag: 2017837359]
+#   14:35:48.353283 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [COOKIE ECHO]
+#   14:35:48.353977 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [COOKIE ACK]
+#   14:35:47.655279 IP CLIENT_IP.PORT > SERVER_IP.PORT: sctp (1) [INIT] [init tag: 2017837359]
+#   (Delayed)
+#   14:35:48.855335 IP SERVER_IP.PORT > CLIENT_IP.PORT: sctp (1) [INIT ACK] [init tag: 164579970]
 #
 # TOPO: SERVER_NS (link0)<--->(link1) ROUTER_NS (link2)<--->(link3) CLIENT_NS
 
 source lib.sh
 
+checktool "nft --version" "run test without nft"
+checktool "tc -h" "run test without tc"
+checktool "modprobe -q sctp" "load sctp module"
+
 CLIENT_IP="198.51.200.1"
 CLIENT_PORT=1234
 
@@ -24,7 +38,8 @@ CLIENT_GW="198.51.200.2"
 SERVER_GW="198.51.100.2"
 
 # setup the topo
-setup() {
+topo_setup() {
+	# setup_ns cleans up existing net namespaces first.
 	setup_ns CLIENT_NS SERVER_NS ROUTER_NS
 	ip -n "$SERVER_NS" link add link0 type veth peer name link1 netns "$ROUTER_NS"
 	ip -n "$CLIENT_NS" link add link3 type veth peer name link2 netns "$ROUTER_NS"
@@ -38,35 +53,53 @@ setup() {
 	ip -n "$ROUTER_NS" addr add $SERVER_GW/24 dev link1
 	ip -n "$ROUTER_NS" addr add $CLIENT_GW/24 dev link2
 	ip net exec "$ROUTER_NS" sysctl -wq net.ipv4.ip_forward=1
+	sysctl -wq net.netfilter.nf_log_all_netns=1
 
 	ip -n "$CLIENT_NS" link set link3 up
 	ip -n "$CLIENT_NS" addr add $CLIENT_IP/24 dev link3
 	ip -n "$CLIENT_NS" route add $SERVER_IP dev link3 via $CLIENT_GW
+}
 
-	# simulate the delay on OVS upcall by setting up a delay for INIT_ACK with
-	# tc on $SERVER_NS side
-	tc -n "$SERVER_NS" qdisc add dev link0 root handle 1: htb r2q 64
-	tc -n "$SERVER_NS" class add dev link0 parent 1: classid 1:1 htb rate 100mbit
-	tc -n "$SERVER_NS" filter add dev link0 parent 1: protocol ip u32 match ip protocol 132 \
-		0xff match u8 2 0xff at 32 flowid 1:1
-	if ! tc -n "$SERVER_NS" qdisc add dev link0 parent 1:1 handle 10: netem delay 1200ms; then
+conf_delay()
+{
+	# simulate the delay on OVS upcall by setting up a delay for INIT_ACK/INIT with
+	local ns=$1
+	local link=$2
+	local chunk_type=$3
+
+	# use a smaller number for assoc's max_retrans to reproduce the issue
+	ip net exec "$CLIENT_NS" sysctl -wq net.sctp.association_max_retrans=3
+
+	tc -n "$ns" qdisc add dev "$link" root handle 1: htb r2q 64
+	tc -n "$ns" class add dev "$link" parent 1: classid 1:1 htb rate 100mbit
+	tc -n "$ns" filter add dev "$link" parent 1: protocol ip \
+		u32 match ip protocol 132 0xff match u8 "$chunk_type" 0xff at 32 flowid 1:1
+	if ! tc -n "$ns" qdisc add dev "$link" parent 1:1 handle 10: netem delay 1200ms; then
 		echo "SKIP: Cannot add netem qdisc"
-		exit $ksft_skip
+		return $ksft_skip
 	fi
 
 	# simulate the ctstate check on OVS nf_conntrack
-	ip net exec "$ROUTER_NS" iptables -A FORWARD -m state --state INVALID,UNTRACKED -j DROP
-	ip net exec "$ROUTER_NS" iptables -A INPUT -p sctp -j DROP
-
-	# use a smaller number for assoc's max_retrans to reproduce the issue
-	modprobe -q sctp
-	ip net exec "$CLIENT_NS" sysctl -wq net.sctp.association_max_retrans=3
+	ip net exec "$ROUTER_NS" nft -f - <<-EOF
+	table ip t {
+		chain forward {
+			type filter hook forward priority filter; policy accept;
+			meta l4proto icmp counter accept
+			ct state new counter accept
+			ct state established,related counter accept
+			ct state invalid log flags all counter drop comment \
+			"Expect to drop stale INIT/INIT_ACK chunks"
+			counter
+		}
+	}
+	EOF
+	return 0
 }
 
 cleanup() {
-	ip net exec "$CLIENT_NS" pkill sctp_collision >/dev/null 2>&1
-	ip net exec "$SERVER_NS" pkill sctp_collision >/dev/null 2>&1
+	# cleanup_all_ns terminates running processes in the namespaces.
 	cleanup_all_ns
+	sysctl -wq net.netfilter.nf_log_all_netns=0
 }
 
 do_test() {
@@ -81,7 +114,15 @@ do_test() {
 
 # run the test case
 trap cleanup EXIT
-setup && \
-echo "Test for SCTP Collision in nf_conntrack:" && \
-do_test && echo "PASS!"
-exit $?
+
+echo "Test for SCTP INIT_ACK Collision in nf_conntrack:"
+(topo_setup && conf_delay $SERVER_NS link0 2) || exit $?
+if ! do_test; then
+	exit $ksft_fail
+fi
+
+echo "Test for SCTP INIT Collision in nf_conntrack:"
+(topo_setup && conf_delay $CLIENT_NS link3 1) || exit $?
+if ! do_test; then
+	exit $ksft_fail
+fi
-- 
2.53.0

Re: [PATCH net v2] selftests: netfilter: conntrack_sctp_collision.sh: Introduce SCTP INIT collision test

[Jakub Kicinski]

On Sun, 19 Apr 2026 03:58:43 +0800 Yi Chen wrote:
> The existing test covered a scenario where a delayed INIT_ACK chunk
> updates the vtag in conntrack after the association has already been
> established.

AI says:

The conntrack_sctp_collision.sh selftest is now failing in the NIPA CI on
both the normal and debug kernel builds:

  not ok 1 1 selftests: net/netfilter: conntrack_sctp_collision.sh # exit=1

  # Test for SCTP INIT_ACK Collision in nf_conntrack:
  # Invalid netns name ""
  # Invalid netns name ""

The root cause is a shell variable scoping bug introduced by this patch.
The new test structure wraps `topo_setup` in a subshell:

  (topo_setup && conf_delay $SERVER_NS link0 2) || exit $?
  if ! do_test; then
      ...
  fi

`topo_setup` calls `setup_ns CLIENT_NS SERVER_NS ROUTER_NS`, which sets
those variables inside the subshell. Those assignments do not propagate
back to the parent shell, so when `do_test` is called afterwards, both
`$SERVER_NS` and `$CLIENT_NS` expand to empty strings. The `ip net exec ""`
calls then fail with "Invalid netns name """.

The second test case (SCTP INIT Collision) would have the same problem.

The fix is to avoid the subshell or ensure the namespace variables are
visible to `do_test`. The simplest approach is to remove the subshell
wrapping and call `topo_setup`, `conf_delay`, and `do_test` in the same
shell scope:

  topo_setup && conf_delay "$SERVER_NS" link0 2 || exit $?
  if ! do_test; then
      exit $ksft_fail
  fi

  topo_setup && conf_delay "$CLIENT_NS" link3 1 || exit $?
  if ! do_test; then
      exit $ksft_fail
  fi

Please also note that `conf_delay` references `$ROUTER_NS` directly
(not via a parameter), so it too requires that those variables be set
in the same shell scope.

Re: [PATCH net v2] selftests: netfilter: conntrack_sctp_collision.sh: Introduce SCTP INIT collision test

[Xin Long]

On Mon, Apr 20, 2026 at 11:23 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Sun, 19 Apr 2026 03:58:43 +0800 Yi Chen wrote:
> > The existing test covered a scenario where a delayed INIT_ACK chunk
> > updates the vtag in conntrack after the association has already been
> > established.
>
> AI says:
>
> The conntrack_sctp_collision.sh selftest is now failing in the NIPA CI on
> both the normal and debug kernel builds:
>
>   not ok 1 1 selftests: net/netfilter: conntrack_sctp_collision.sh # exit=1
>
>   # Test for SCTP INIT_ACK Collision in nf_conntrack:
>   # Invalid netns name ""
>   # Invalid netns name ""
>
> The root cause is a shell variable scoping bug introduced by this patch.
> The new test structure wraps `topo_setup` in a subshell:
>
>   (topo_setup && conf_delay $SERVER_NS link0 2) || exit $?
Better to change it to:

topo_setup || exit $?
conf_delay $SERVER_NS link0 2 || exit $?

Again, please do not post the patch until the fix gets merged into net.git:

https://lore.kernel.org/netdev/cover.1775847557.git.lucien.xin@gmail.com/

Otherwise, it will still be failing in the NIPA CI.

Thanks.

>   if ! do_test; then
>       ...
>   fi
>
> `topo_setup` calls `setup_ns CLIENT_NS SERVER_NS ROUTER_NS`, which sets
> those variables inside the subshell. Those assignments do not propagate
> back to the parent shell, so when `do_test` is called afterwards, both
> `$SERVER_NS` and `$CLIENT_NS` expand to empty strings. The `ip net exec ""`
> calls then fail with "Invalid netns name """.
>
> The second test case (SCTP INIT Collision) would have the same problem.
>
> The fix is to avoid the subshell or ensure the namespace variables are
> visible to `do_test`. The simplest approach is to remove the subshell
> wrapping and call `topo_setup`, `conf_delay`, and `do_test` in the same
> shell scope:
>
>   topo_setup && conf_delay "$SERVER_NS" link0 2 || exit $?
>   if ! do_test; then
>       exit $ksft_fail
>   fi
>
>   topo_setup && conf_delay "$CLIENT_NS" link3 1 || exit $?
>   if ! do_test; then
>       exit $ksft_fail
>   fi
>
> Please also note that `conf_delay` references `$ROUTER_NS` directly
> (not via a parameter), so it too requires that those variables be set
> in the same shell scope.