[PATCH net-next] selftests/net/openvswitch: add output truncation test

[PATCH net-next] selftests/net/openvswitch: add output truncation test

[Minxi Hou]

Add test_trunc exercising the OVS_ACTION_ATTR_TRUNC action. The test
verifies truncation in three steps: first confirm normal forwarding
works, then apply trunc(14) which truncates packets to the Ethernet
header and verify ping fails, then restore normal forwarding and
verify connectivity recovers.

The trunc action sets OVS_CB(skb)->cutlen, causing pskb_trim at
output time. With trunc(14) the IP payload is stripped, so the
receiver drops the frame and ICMP echo reply is never generated.

Signed-off-by: Minxi Hou <houminxi@gmail.com>
---
 .../selftests/net/openvswitch/openvswitch.sh  | 66 +++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh b/tools/testing/selftests/net/openvswitch/openvswitch.sh
index 82f066a0ceed..181eeb332de9 100755
--- a/tools/testing/selftests/net/openvswitch/openvswitch.sh
+++ b/tools/testing/selftests/net/openvswitch/openvswitch.sh
@@ -30,6 +30,7 @@ tests="
 	drop_reason				drop: test drop reasons are emitted
 	pop_vlan				vlan: POP_VLAN action strips tag
 	dec_ttl					ttl: dec_ttl decrements IP TTL
+	trunc					trunc: output truncation
 	psample					psample: Sampling packets with psample"
 
 info() {
@@ -300,6 +301,71 @@ test_dec_ttl() {
 	return 0
 }
 
+test_trunc() {
+	sbx_add "test_trunc" || return $?
+	ovs_add_dp "test_trunc" trunctest || return 1
+
+	info "create namespaces"
+	for ns in client server; do
+		ovs_add_netns_and_veths "test_trunc" "trunctest" "$ns" \
+			"${ns:0:1}0" "${ns:0:1}1" || return 1
+	done
+
+	ip netns exec client ip addr add 10.0.0.1/24 dev c1
+	ip netns exec client ip link set c1 up
+	ip netns exec server ip addr add 10.0.0.2/24 dev s1
+	ip netns exec server ip link set s1 up
+
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
+
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0800),ipv4()' '2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
+
+	info "verify connectivity without truncation"
+	ovs_sbx "test_trunc" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 || return 1
+
+	ovs_del_flows "test_trunc" trunctest
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
+
+	info "add truncated forwarding flow"
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0800),ipv4()' \
+		'trunc(14),2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
+
+	info "verify ping fails with truncation"
+	ovs_sbx "test_trunc" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 >/dev/null 2>&1 \
+		&& { info "FAIL: ping should fail with trunc(14)"
+		     return 1; }
+
+	ovs_del_flows "test_trunc" trunctest
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(1),eth(),eth_type(0x0800),ipv4()' '2' || return 1
+	ovs_add_flow "test_trunc" trunctest \
+		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
+
+	info "verify connectivity restored without truncation"
+	ovs_sbx "test_trunc" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 || return 1
+
+	return 0
+}
+
 # psample test
 # - use psample to observe packets
 test_psample() {
-- 
2.54.0

Re: [PATCH net-next] selftests/net/openvswitch: add output truncation test

[Jakub Kicinski]

On Fri, 12 Jun 2026 00:25:37 +0800 Minxi Hou wrote:
> Add test_trunc exercising the OVS_ACTION_ATTR_TRUNC action. The test
> verifies truncation in three steps: first confirm normal forwarding
> works, then apply trunc(14) which truncates packets to the Ethernet
> header and verify ping fails, then restore normal forwarding and
> verify connectivity recovers.
> 
> The trunc action sets OVS_CB(skb)->cutlen, causing pskb_trim at
> output time. With trunc(14) the IP payload is stripped, so the
> receiver drops the frame and ICMP echo reply is never generated.

Does not apply. 

Please note that net-next is closed for the duration of the merge
window so you'll have to wait 2 weeks with the repost.
-- 
pw-bot: cr