Re: [PATCH net v2] net: 802: LLC+SNAP OID:PID lookup on start of skb data

[Eric Dumazet]

On Fri, Jan 3, 2025 at 2:23 AM Antonio Pastor <antonio.pastor@xxxxxxxxx> wrote:
>
> 802.2+LLC+SNAP frames received by napi_complete_done() with GRO and DSA
> have skb->transport_header set two bytes short, or pointing 2 bytes
> before network_header & skb->data. This was an issue as snap_rcv()
> expected offset to point to SNAP header (OID:PID), causing packet to
> be dropped.
>
> A fix at llc_fixup_skb() (a024e377efed) resets transport_header for any
> LLC consumers that may care about it, and stops SNAP packets from being
> dropped, but doesn't fix the problem which is that LLC and SNAP should
> not use transport_header offset.
>
> Ths patch eliminates the use of transport_header offset for SNAP lookup
> of OID:PID so that SNAP does not rely on the offset at all.
> The offset is reset after pull for any SNAP packet consumers that may
> (but shouldn't) use it.
>
> Fixes: fda55eca5a33 ("net: introduce skb_transport_header_was_set()")
> Signed-off-by: Antonio Pastor <antonio.pastor@xxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>