Re: [PATCH net] net: lapb: Copy the skb before sending a packet

[Martin Schiller]

On 2021-02-01 11:49, Xie He wrote:
> On Mon, Feb 1, 2021 at 2:05 AM Martin Schiller <ms@xxxxxxxxxx> wrote:
> > What kind of packages do you mean are corrupted?
> > ETH_P_X25 or ETH_P_HDLC?
>
> I mean ETH_P_X25. I was using "lapbether.c" to test so there was no 
> ETH_P_HDLC.
>
> > I have also sent a patch here in the past that addressed corrupted
> > ETH_P_X25 frames on an AF_PACKET socket:
> >
> > https://lkml.org/lkml/2020/1/13/388
> >
> > Unfortunately I could not track and describe exactly where the problem
> > was.
>
> Ah... Looks like we had the same problem.
>
> > I just wonder when/where is the logically correct place to copy the 
> > skb.
> > Shouldn't it be copied before removing the pseudo header (as I did in 
> > my
> > patch)?
>
> I think it's not necessary to copy it before removing the pseudo
> header, because "skb_pull" will not change any data in the data
> buffer. "skb_pull" will only change the values of "skb->data" and
> "skb->len". These values are not shared between clones of skbs, so
> it's safe to change them without affecting other clones of the skb.
>
> I also choose to copy the skb in the LAPB module (rather than in the
> drivers) because I see all drivers have this problem (including the
> recently deleted x25_asy.c driver), so it'd be better to fix this
> issue in the LAPB module, for all drivers.

OK.

Acked-by: Martin Schiller <ms@xxxxxxxxxx>