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selftests/bpf: Fix test_maps sockmap failure

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test_maps fails in the sockmap test because sockmap_verdict_prog.c
drops the packet when the first 8 bytes are not directly accessible:
	  if (data + 8 > data_end)
			  return SK_DROP;

The blamed commit removed bpf_skb_pull_data() from the stream parser
program so that the parser no longer modifies the skb. That was needed,
but it also removed an implicit side effect: bpf_skb_pull_data()
linearized enough of the skb for later direct packet access.

In this test, the send side goes through the sockmap SK_MSG path. The
skb can have skb->len == 20 while its linear area is empty, so the
verdict program sees data == data_end and drops the packet even though
the payload length is sufficient.

Keep the parser read-only, and pull the first 8 bytes in the verdict
program before reading or writing them. Reload data/data_end after
bpf_skb_pull_data() as required.

Fixes: 22a0cc10da ("selftests/bpf: don't modify the skb in the strparser parser prog")
Reported-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260701071501.39628-1-jiayuan.chen@linux.dev

Closes: https://lore.kernel.org/bpf/e3a91acd-2b4d-4e93-a3bb-a0e9ee5ede0f@linux.dev/
This commit is contained in:
Jiayuan Chen 2026-07-01 15:14:22 +08:00 committed by Andrii Nakryiko
parent 475b59db3b
commit 27a0f3635d
1 changed files with 12 additions and 2 deletions
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14
tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c
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@ -44,8 +44,18 @@ int bpf_prog2(struct __sk_buff *skb)
__sink(lport);
__sink(rport);
if (data + 8 > data_end)
return SK_DROP;
if (data + 8 > data_end) {
if (bpf_skb_pull_data(skb, 8))
return SK_DROP;
data = (void *)(long)skb->data;
data_end = (void *)(long)skb->data_end;
if (data + 8 > data_end)
return SK_DROP;
d = data;
}
map = d[0];
sk = d[1];