Re: [QUESTION] BPF_SK_SKB_STREAM_PARSER cannot observe strparser orig_offset?

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 5/11/26 10:49 PM, Cristian Morales Vega (cmorve) wrote:
> I am trying to use BPF_SK_SKB_STREAM_VERDICT in an old kernel (I don't have control over the version), so I need to also use BPF_SK_SKB_STREAM_PARSER. I though to just do "return skb->len;" in it, as a no-op, since I don't really have an use for the parser.

Since v5.18 BPF_SK_SKB_STREAM_VERDICT can be used without 
BPF_SK_SKB_STREAM_PARSER.

Which kernel version you use now?

>
> So far so good. But I can see that, from time to time, __strp_recv() receives a non-zero orig_offset as "first skb" (i.e. strp->skb_head is null). In such a case, I should not be returning skb->len but "skb->len - orig_offset" (i.e. orig_len), right? Otherwise I would enter
>
> 		extra = (ssize_t)(stm->accum_len + cand_len) -
> 			stm->strp.full_len;
>
> 		if (extra < 0) {
> 			/* Message not complete yet. */
>
> But AFAICT BPF_SK_SKB_STREAM_PARSER doesn't have access to that offset. It seems it had it until e0dc3b93bd7bcff8c3813d1df43e0908499c7cf0 (which was backported), but not any more?
>
> Is my understanding correct? If not, what am I missing? And, if yes, there is any solution?


If you just return skb->len only in your parser , the 'issue' should not 
happen.