[PATCH net v1 2/2] selftests/bpf: add test for xdp_bonding xmit_hash_policy compat

[Jiayuan Chen <jiayuan.chen@linux.dev>]

From: Jiayuan Chen <jiayuan.chen@shopee.com>

Add a selftest to verify that changing xmit_hash_policy to vlan+srcmac
is rejected when a native XDP program is loaded on a bond in 802.3ad
mode.  Without the fix in bond_option_xmit_hash_policy_set(), the change
succeeds silently, creating an inconsistent state that triggers a kernel
WARNING in dev_xdp_uninstall() when the bond is torn down.

The test attaches native XDP to a bond0 (802.3ad, layer2+3), then
attempts to switch xmit_hash_policy to vlan+srcmac and asserts the
operation fails.  It also verifies the change succeeds after XDP is
detached, confirming the rejection is specific to the XDP-loaded state.

Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
---
 .../selftests/bpf/prog_tests/xdp_bonding.c    | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
index a5b15e464018..0d4ec1e5b401 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
@@ -704,6 +704,61 @@ static void test_xdp_bonding_features(struct skeletons *skeletons)
 	system("ip link del bond");
 }
 
+/*
+ * Test that changing xmit_hash_policy to vlan+srcmac is rejected when a
+ * native XDP program is loaded on a bond in 802.3ad or balance-xor mode.
+ * These modes support XDP only when xmit_hash_policy != vlan+srcmac; freely
+ * changing the policy creates an inconsistency that triggers a WARNING in
+ * dev_xdp_uninstall() during device teardown.
+ */
+static void test_xdp_bonding_xmit_policy_compat(struct skeletons *skeletons)
+{
+	struct nstoken *nstoken = NULL;
+	int bond_ifindex = -1;
+	int xdp_fd, err;
+
+	SYS(out, "ip netns add ns_xmit_policy");
+	nstoken = open_netns("ns_xmit_policy");
+	if (!ASSERT_OK_PTR(nstoken, "open ns_xmit_policy"))
+		goto out;
+
+	/* 802.3ad with layer2+3 policy: native XDP is supported */
+	SYS(out, "ip link add bond0 type bond mode 802.3ad xmit_hash_policy layer2+3");
+	SYS(out, "ip link add veth0 type veth peer name veth0p");
+	SYS(out, "ip link set veth0 master bond0");
+	SYS(out, "ip link set bond0 up");
+
+	bond_ifindex = if_nametoindex("bond0");
+	if (!ASSERT_GT(bond_ifindex, 0, "bond0 ifindex"))
+		goto out;
+
+	xdp_fd = bpf_program__fd(skeletons->xdp_dummy->progs.xdp_dummy_prog);
+	if (!ASSERT_GE(xdp_fd, 0, "xdp_dummy fd"))
+		goto out;
+
+	err = bpf_xdp_attach(bond_ifindex, xdp_fd, XDP_FLAGS_DRV_MODE, NULL);
+	if (!ASSERT_OK(err, "attach XDP to bond0"))
+		goto out;
+
+	/* With XDP loaded, switching to vlan+srcmac must be rejected */
+	err = system("ip link set bond0 type bond xmit_hash_policy vlan+srcmac 2>/dev/null");
+	ASSERT_NEQ(err, 0, "vlan+srcmac change with XDP loaded should fail");
+
+	/* Detach XDP first, then the same change must succeed */
+	ASSERT_OK(bpf_xdp_detach(bond_ifindex, XDP_FLAGS_DRV_MODE, NULL),
+		  "detach XDP from bond0");
+
+	bond_ifindex = -1;
+	err = system("ip link set bond0 type bond xmit_hash_policy vlan+srcmac 2>/dev/null");
+	ASSERT_OK(err, "vlan+srcmac change without XDP should succeed");
+
+out:
+	if (bond_ifindex > 0)
+		bpf_xdp_detach(bond_ifindex, XDP_FLAGS_DRV_MODE, NULL);
+	close_netns(nstoken);
+	SYS_NOFAIL("ip netns del ns_xmit_policy");
+}
+
 static int libbpf_debug_print(enum libbpf_print_level level,
 			      const char *format, va_list args)
 {
@@ -771,6 +826,9 @@ void serial_test_xdp_bonding(void)
 				test_case->xmit_policy);
 	}
 
+	if (test__start_subtest("xdp_bonding_xmit_policy_compat"))
+		test_xdp_bonding_xmit_policy_compat(&skeletons);
+
 	if (test__start_subtest("xdp_bonding_redirect_multi"))
 		test_xdp_bonding_redirect_multi(&skeletons);
 
-- 
2.43.0