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

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Message-ID: <afaadf5e-556c-4fd6-bfd3-9c486a35a08f@quicinc.com>
Date:   Wed, 25 Oct 2023 08:52:23 -0700
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Johannes Berg <johannes@...solutions.net>,
        Kalle Valo <kvalo@...nel.org>
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 10/24/2023 7:37 PM, Gustavo A. R. Silva wrote:
> 
> 
> 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.

I'm seeing clarification from the development team.

/jeff