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Subject: Re: [RFC - is this a bug?] wifi: ath10k: Asking for some light on
 this, please :)
From:   Johannes Berg <johannes@sipsolutions.net>
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Kalle Valo <kvalo@kernel.org>,
        Jeff Johnson <quic_jjohnson@quicinc.com>
Cc:     ath10k@lists.infradead.org, linux-wireless@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        linux-hardening@vger.kernel.org
Date:   Tue, 24 Oct 2023 22:49:29 +0200
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On Tue, 2023-10-24 at 14:41 -0600, Gustavo A. R. Silva wrote:
>=20
> 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):
>=20
> 	8920         memset(skb->data, 0, sizeof(*cmd));
>=20
> Notice that if `cap->peer_chan_len =3D=3D 0` or `cap->peer_chan_len =3D=
=3D 1`,
> in the original code, we have `len =3D=3D sizeof(*cmd) =3D=3D 128`:

Right.

> -       /* tdls peer update cmd has place holder for one channel*/
> -       chan_len =3D cap->peer_chan_len ? (cap->peer_chan_len - 1) : 0;
> -
> -       len =3D sizeof(*cmd) + chan_len * sizeof(*chan);
> +       len =3D struct_size(cmd, peer_capab.peer_chan_list, cap->peer_cha=
n_len);
>=20
>          skb =3D ath10k_wmi_alloc_skb(ar, len);
>          if (!skb)
>=20
> which makes `round_len =3D=3D roundup(len, 4) =3D=3D struct_size(cmd,...,=
...) =3D=3D 104`
> when `cap->peer_chan_len =3D=3D 0`

And yeah, that's really the issue, it only matters for =3D=3D0. For a momen=
t
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 =3D min(cap->peer_chan_len, 1);

for the struct_size()?

johannes