Re: [RFC - is this a bug?] wifi: ath10k: Asking for some light on this, please :)

[Gustavo A. R. Silva]

On 10/24/23 14:49, Johannes Berg wrote:
> On Tue, 2023-10-24 at 14:41 -0600, Gustavo A. R. Silva wrote:
> > It seems we run into the same issue in the function below, even in the
> > case this `memset()` is unnecessary (which it seems it's not):
> >
> > 	8920         memset(skb->data, 0, sizeof(*cmd));
> >
> > Notice that if `cap->peer_chan_len == 0` or `cap->peer_chan_len == 1`,
> > in the original code, we have `len == sizeof(*cmd) == 128`:
>
> Right.
>
> > -       /* tdls peer update cmd has place holder for one channel*/
> > -       chan_len = cap->peer_chan_len ? (cap->peer_chan_len - 1) : 0;
> > -
> > -       len = sizeof(*cmd) + chan_len * sizeof(*chan);
> > +       len = struct_size(cmd, peer_capab.peer_chan_list, cap->peer_chan_len);
> >
> >           skb = ath10k_wmi_alloc_skb(ar, len);
> >           if (!skb)
> >
> > which makes `round_len == roundup(len, 4) == struct_size(cmd,...,...) == 104`
> > when `cap->peer_chan_len == 0`
>
> And yeah, that's really the issue, it only matters for ==0. For a moment
> there I thought that doesn't even make sense, but it looks like it never
> even becomes non-zero.
>
> No idea then, sorry. You'd hope firmware doesn't care about the actual
> message size if the inner data says "0 entries", but who knows? And how
> many firmware versions are there? :)
>
> So I guess you'd want to stay compatible, even if it means having a
>
> 	chan_len = min(cap->peer_chan_len, 1);
>
> for the struct_size()?

Yeah, that's an alternative.

I'll wait for the maintainers to chime in and see if they have a different
opinion.

Thanks
--
Gustavo