On Mon, Jul 13, 2020 at 2:21 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
>
> It is not clear to me what guarantee we have to have one byte of headroom in
> the skb
> at this point.
>
> You might add to be safe : (as done in lapbeth_data_indication(), but after
> the skb_push() which seems wrong)
>
> if (skb_cow(skb, 1)) {
> kfree_skb(skb); /* This line I am not sure, but looking at
> * lapb_data_indication() this might be needed.
> */
> return NET_RX_DROP;
> }
>
Thank you for your review, Eric!
The function "x25_asy_data_indication" is called by the "lapb" module
(net/lapb/). Before the "lapb" module calls this function, it has
removed from the skb an LAPB header which is at least 2 bytes (in the
function "lapb_decode"). So I thought there would always be a headroom
of one byte at this point.
But yes, it is always safer to add "skb_cow" at this point, so that it
is clearer the code would not crash here. I'll add it in the second
version of this patch. Thank you for your suggestion!
And yes, I agree that in "lapbeth_data_indication", the order of
"skb_push" and "skb_cow" is probably wrong. Let us submit another
patch to fix this problem!
