selftests/net/openvswitch: add flow modify test

Add mod_flow() and the mod-flow CLI command to ovs-dpctl.py, exercising
OVS_FLOW_CMD_SET. Add test_flow_set which first modifies an existing
flow with new actions and verifies the change via traffic, then modifies
the same flow without actions and verifies the kernel handles the
no-actions case gracefully.

The no-actions path is unreachable from userspace OVS tools (dpctl
mod-flow requires actions) but reachable via raw netlink. This is the
code path where Adrian Moreno found a possible kfree_skb of ERR_PTR
when reply allocation fails after locking.

Make parse() skip OVS_FLOW_ATTR_ACTIONS when actstr is None so the
kernel enters the post-lock allocation branch in ovs_flow_cmd_set().
After the no-actions set, verify via dump-flows that the flow retained
its drop action.

Suggested-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Minxi Hou <houminxi@gmail.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/20260609165725.107484-1-houminxi@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 114 insertions, 3 deletions

diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh b/tools/testing/selftests/net/openvswitch/openvswitch.sh
index 82f066a0ceed..d533decca5c1 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
+	flow_set				flow-set: Flow modify
 	psample					psample: Sampling packets with psample"
 
 info() {
@@ -193,6 +194,23 @@ ovs_add_flow () {
 	return 0
 }
 
+ovs_mod_flow () {
+	if [ -n "$4" ]; then
+		info "Modifying flow: sbx:$1 br:$2 flow:$3 act:$4"
+		ovs_sbx "$1" python3 $ovs_base/ovs-dpctl.py \
+			mod-flow "$2" "$3" "$4"
+	else
+		info "Modifying flow (no actions): sbx:$1 br:$2 flow:$3"
+		ovs_sbx "$1" python3 $ovs_base/ovs-dpctl.py \
+			mod-flow "$2" "$3"
+	fi
+	if [ $? -ne 0 ]; then
+		info "Flow modify [ $3 ] failed"
+		return 1
+	fi
+	return 0
+}
+
 ovs_del_flows () {
 	info "Deleting all flows from DP: sbx:$1 br:$2"
 	ovs_sbx "$1" python3 $ovs_base/ovs-dpctl.py del-flows "$2"
@@ -300,6 +318,65 @@ test_dec_ttl() {
 	return 0
 }
 
+test_flow_set() {
+	sbx_add "test_flow_set" || return $?
+	ovs_add_dp "test_flow_set" flowset || return 1
+
+	info "create namespaces"
+	for ns in client server; do
+		ovs_add_netns_and_veths "test_flow_set" "flowset" "$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_flow_set" flowset \
+		'in_port(1),eth(),eth_type(0x0806),arp()' '2' || return 1
+	ovs_add_flow "test_flow_set" flowset \
+		'in_port(2),eth(),eth_type(0x0806),arp()' '1' || return 1
+
+	local fwd_flow="ufid:00000001-0002-0003-0004-000500060007"
+	fwd_flow="$fwd_flow,in_port(1),eth(),eth_type(0x0800),ipv4()"
+
+	ovs_add_flow "test_flow_set" flowset "$fwd_flow" '2' \
+		|| return 1
+	ovs_add_flow "test_flow_set" flowset \
+		'in_port(2),eth(),eth_type(0x0800),ipv4()' '1' || return 1
+
+	info "verify initial forwarding"
+	ovs_sbx "test_flow_set" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 || return 1
+
+	info "mod-flow with new actions (change to drop)"
+	ovs_mod_flow "test_flow_set" flowset "$fwd_flow" 'drop' \
+		|| return 1
+
+	info "verify traffic is now dropped"
+	ovs_sbx "test_flow_set" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 >/dev/null 2>&1 \
+		&& { info "FAIL: ping should fail after mod-flow to drop"
+		     return 1; }
+
+	info "mod-flow without actions"
+	ovs_mod_flow "test_flow_set" flowset "$fwd_flow" || return 1
+
+	info "verify flow retained drop action via dump"
+	python3 "$ovs_base/ovs-dpctl.py" dump-flows flowset \
+		| grep -q "actions:drop" || \
+		{ info "FAIL: flow not showing drop action"; return 1; }
+
+	info "verify drop actions unchanged"
+	ovs_sbx "test_flow_set" ip netns exec client ping -c 1 -W 2 \
+		10.0.0.2 >/dev/null 2>&1 \
+		&& { info "FAIL: ping should still fail after no-actions set"
+		     return 1; }
+
+	return 0
+}
+
 # psample test
 # - use psample to observe packets
 test_psample() {
diff --git a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
index 3342e295293d..e1ecfad2c03e 100644
--- a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
+++ b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
@@ -2702,9 +2702,10 @@ class OvsFlow(GenericNetlinkSocket):
             self["attrs"].append(["OVS_FLOW_ATTR_KEY", k])
             self["attrs"].append(["OVS_FLOW_ATTR_MASK", m])
 
-            a = ovsactions()
-            a.parse(actstr)
-            self["attrs"].append(["OVS_FLOW_ATTR_ACTIONS", a])
+            if actstr is not None:
+                a = ovsactions()
+                a.parse(actstr)
+                self["attrs"].append(["OVS_FLOW_ATTR_ACTIONS", a])
 
     def __init__(self):
         GenericNetlinkSocket.__init__(self)
@@ -2738,6 +2739,25 @@ class OvsFlow(GenericNetlinkSocket):
             raise ne
         return reply
 
+    def mod_flow(self, dpifindex, flowmsg):
+        """Modify an existing flow in the kernel."""
+        flowmsg["cmd"] = OVS_FLOW_CMD_SET
+        flowmsg["version"] = OVS_DATAPATH_VERSION
+        flowmsg["reserved"] = 0
+        flowmsg["dpifindex"] = dpifindex
+
+        try:
+            reply = self.nlm_request(
+                flowmsg,
+                msg_type=self.prid,
+                msg_flags=NLM_F_REQUEST | NLM_F_ACK,
+            )
+            reply = reply[0]
+        except NetlinkError as ne:
+            print(flowmsg)
+            raise ne
+        return reply
+
     def del_flows(self, dpifindex):
         """
         Send a del message to the kernel that will drop all flows.
@@ -3013,6 +3033,12 @@ def main(argv):
     addflcmd.add_argument("flow", help="Flow specification")
     addflcmd.add_argument("acts", help="Flow actions")
 
+    modflcmd = subparsers.add_parser("mod-flow")
+    modflcmd.add_argument("modbr", help="Datapath name")
+    modflcmd.add_argument("modflow", help="Flow specification")
+    modflcmd.add_argument("modacts", help="Flow actions",
+                          nargs="?", default=None)
+
     delfscmd = subparsers.add_parser("del-flows")
     delfscmd.add_argument("flsbr", help="Datapath name")
 
@@ -3110,6 +3136,14 @@ def main(argv):
         flow = OvsFlow.ovs_flow_msg()
         flow.parse(args.flow, args.acts, rep["dpifindex"])
         ovsflow.add_flow(rep["dpifindex"], flow)
+    elif hasattr(args, "modbr"):
+        rep = ovsdp.info(args.modbr, 0)
+        if rep is None:
+            print(f"DP '{args.modbr}' not found.")
+            return 1
+        flow = OvsFlow.ovs_flow_msg()
+        flow.parse(args.modflow, args.modacts, rep["dpifindex"])
+        ovsflow.mod_flow(rep["dpifindex"], flow)
     elif hasattr(args, "flsbr"):
         rep = ovsdp.info(args.flsbr, 0)
         if rep is None: