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SubjectRe: [PATCH v2 1/1] xfrm: Use skb_mac_header_was_set() to check for MAC header presence
Hi Paolo,

On 9/5/23 11:59, Paolo Abeni wrote:
> On Mon, 2023-09-04 at 12:32 +0200, Marcello Sylvester Bauer wrote:
>> From: Marcello Sylvester Bauer <sylv@sylv.io>
>>
>> Add skb_mac_header_was_set() in xfrm4_remove_tunnel_encap() and
>> xfrm6_remove_tunnel_encap() to detect the presence of a MAC header.
>> This change prevents a kernel page fault on a non-zero mac_len when the
>> mac_header is not set.
>>
>> Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
>
> Please include a suitable fixes tag.
>
> Please also include in the commit message the stacktrace:
>
> https://lore.kernel.org/netdev/636d3434-d47a-4cd4-b3ba-7f7254317b64@sylv.io/
>
> trimming the asm code and lines starting with ' ? '

Sure, will be added to the next version in addition to a cover letter to
give additional context to this patch.

>
> I think the real issue could be elsewhere, we should not reach here
> with mac_len > 0 && !skb_mac_header_was_set().
>
> Could you please try the following debug patch in your setup, and see
> if hints at some other relevant place?

Unfortunately the person with the hardware is OOO for two weeks. But I
could ask him to test it when he gets back.

Thanks,
Marcello

>
> Thanks,
>
> Paolo
>
> ---
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 4174c4b82d13..38ca2c7e50ca 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2793,6 +2793,7 @@ static inline void skb_reset_inner_headers(struct sk_buff *skb)
>
> static inline void skb_reset_mac_len(struct sk_buff *skb)
> {
> + WARN_ON_ONCE(!skb_mac_header_was_set(skb));
> skb->mac_len = skb->network_header - skb->mac_header;
> }
>
>

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