selftests/bpf: Cover skb metadata access after bpf_skb_change_proto

Add a test to verify that skb metadata remains accessible after calling
bpf_skb_change_proto(), which modifies packet headroom to accommodate
different IP header sizes.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20251105-skb-meta-rx-path-v4-16-5ceb08a9b37b@cloudflare.com

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
index 65735a134abb85c8a7b363a3853175592053da36..ee94c281888ae0ea0da37c0c69c9ac4af2d13411 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -502,6 +502,11 @@ void test_xdp_context_tuntap(void)
                            skel->progs.helper_skb_change_head_tail,
                            NULL, /* tc prio 2 */
                            &skel->bss->test_pass);
+       if (test__start_subtest("helper_skb_change_proto"))
+               test_tuntap(skel->progs.ing_xdp,
+                           skel->progs.helper_skb_change_proto,
+                           NULL, /* tc prio 2 */
+                           &skel->bss->test_pass);
 
        test_xdp_meta__destroy(skel);
 }

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_meta.c b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
index e0b2e8ed0cc5108e5818f042367d35f75ae03d22..0a0f371a2deccda35cc0e39f386fc2c5f9368e02 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_xdp_meta.c
+++ b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
@@ -4,6 +4,7 @@
 #include <linux/if_ether.h>
 #include <linux/pkt_cls.h>
 
+#include <bpf/bpf_endian.h>
 #include <bpf/bpf_helpers.h>
 #include "bpf_kfuncs.h"
 
@@ -645,4 +646,28 @@ out:
        return TC_ACT_SHOT;
 }
 
+SEC("tc")
+int helper_skb_change_proto(struct __sk_buff *ctx)
+{
+       int err;
+
+       err = bpf_skb_change_proto(ctx, bpf_htons(ETH_P_IPV6), 0);
+       if (err)
+               goto out;
+
+       if (!check_skb_metadata(ctx))
+               goto out;
+
+       err = bpf_skb_change_proto(ctx, bpf_htons(ETH_P_IP), 0);
+       if (err)
+               goto out;
+
+       if (!check_skb_metadata(ctx))
+               goto out;
+
+       test_pass = true;
+out:
+       return TC_ACT_SHOT;
+}
+
 char _license[] SEC("license") = "GPL";