selftests/bpf: add test for xdp_bonding xmit_hash_policy compat

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>
Link: https://patch.msgid.link/20260226080306.98766-3-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
index fb952703653e48e0340730fb7ff0edaf2b191482..e8ea264643491fa596b56a330f833218302ba381 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
@@ -610,6 +610,61 @@ out:
        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)
 {
@@ -677,6 +732,9 @@ 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);