[PATCH net-next 4/5] selftests/bpf: check XDP attach on a nested bond slave

[Jakub Kicinski <kuba@kernel.org>]

test_xdp_bonding_attach() already covers a flat bond both ways round:
the master is refused while a slave has a program, and a slave is
refused while the master has one. The nested test only ever checked
that attaching to the outermost master succeeds.

That left the more interesting half of the nesting untested. With
bond -> bond_nest1 -> bond_nest2, bond_nest2 refuses a program of its
own only if the program the outer bond pushed down is recorded on it.
Before "net: record XDP programs propagated to lower devices" it was
recorded nowhere, and a second program could be attached to bond_nest2
while the outer bond's was already running on it. Check that the attach
is refused, and with -EBUSY, which is what the recorded program gives.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 .../selftests/bpf/prog_tests/xdp_bonding.c    | 24 ++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
index c42488e445c2..ab0f01be4131 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_bonding.c
@@ -461,11 +461,15 @@ static void test_xdp_bonding_attach(struct skeletons *skeletons)
 	system("ip link del vxlan");
 }
 
-/* Test with nested bonding devices to catch issue with negative jump label count */
+/*
+ * Test with nested bonding devices to catch issue with negative jump label
+ * count, and check that a nested slave refuses a program of its own.
+ */
 static void test_xdp_bonding_nested(struct skeletons *skeletons)
 {
+	struct bpf_link *link2 = NULL;
 	struct bpf_link *link = NULL;
-	int bond, err;
+	int bond, nest2, err;
 
 	if (!ASSERT_OK(system("ip link add bond type bond"), "add bond"))
 		goto out;
@@ -488,10 +492,24 @@ static void test_xdp_bonding_nested(struct skeletons *skeletons)
 	if (!ASSERT_OK(err, "set bond_nest2 master"))
 		goto out;
 
+	nest2 = if_nametoindex("bond_nest2");
+	if (!ASSERT_GT(nest2, 0, "if_nametoindex bond_nest2"))
+		goto out;
+
 	link = bpf_program__attach_xdp(skeletons->xdp_dummy->progs.xdp_dummy_prog, bond);
-	ASSERT_OK_PTR(link, "attach program to master");
+	if (!ASSERT_OK_PTR(link, "attach program to master"))
+		goto out;
+
+	/*
+	 * Attaching to a nested slave is not allowed either. The program the
+	 * outer bond pushed down is recorded there too.
+	 */
+	link2 = bpf_program__attach_xdp(skeletons->xdp_dummy->progs.xdp_dummy_prog, nest2);
+	ASSERT_EQ(libbpf_get_error(link2), -EBUSY,
+		  "attach program to nested slave when master has program");
 
 out:
+	bpf_link__destroy(link2);
 	bpf_link__destroy(link);
 	system("ip link del bond");
 	system("ip link del bond_nest1");
-- 
2.56.0