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selftests/bpf: Fix test_maps sockmap failure

PATCH Applied Jiayuan Chen 2 participants 2 messages Jul 1

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Kselftest BPF BPF selftests
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Jiayuan Chen

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#0 lore raw

PATCH 1/1 selftests/bpf: Fix test_maps sockmap failure

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.

Reported-by Ihor Solodrai <[email protected]>
Closes https://lore.kernel.org/bpf/[email protected]/ open here
Fixes 22a0cc10dacb ("selftests/bpf: don't modify the skb in the strparser parser prog")
Signed-off-by Jiayuan Chen <[email protected]>
---
 .../selftests/bpf/progs/sockmap_verdict_prog.c     | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
tools/testing/selftests/bpf/progs/sockmap_verdict_prog.c +12 -2
index 0660f29dca955..3177bc5b733ac 100644
@@ -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];
Signature · 1 line
2.43.0
CI Applied
#1 lore raw
This patch was applied to bpf/bpf-next.git (master) by Andrii Nakryiko <[email protected]>:

Hello:

This patch was applied to bpf/bpf-next.git (master) by Andrii Nakryiko <[email protected]>:

Quoted 11 lines · On Wed, 1 Jul 2026 15:14:22 +0800 you wrote:

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.

[...]

Here is the summary with links:
- [bpf,v1] selftests/bpf: Fix test_maps sockmap failure

    https://git.kernel.org/bpf/bpf-next/c/27a0f3635d86

You are awesome, thank you!

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