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

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Date: Tue, 24 Oct 2023 22:49:29 +0200
From: Johannes Berg <johannes@...solutions.net>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>, Kalle Valo
	 <kvalo@...nel.org>, Jeff Johnson <quic_jjohnson@...cinc.com>
Cc: ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org, 
 linux-kernel@...r.kernel.org, "Gustavo A. R. Silva"
 <gustavoars@...nel.org>,  linux-hardening@...r.kernel.org
Subject: Re: [RFC - is this a bug?] wifi: ath10k: Asking for some light on
 this, please :)

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()?

johannes