linux-kernel - Re: [PATCH 6/6] wifi: ath10k: remove duplicate memset() in 10.4 TDLS peer update

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Message-ID: <bdabfb74-ea4f-4455-bb4c-1d93977393ea@quicinc.com>
Date:   Wed, 13 Dec 2023 11:36:08 -0800
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Kalle Valo <kvalo@...nel.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        <ath10k@...ts.infradead.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] wifi: ath10k: remove duplicate memset() in 10.4 TDLS
 peer update

On 12/13/2023 11:16 AM, Kees Cook wrote:
> On Wed, Dec 13, 2023 at 09:06:44AM -0800, Jeff Johnson wrote:
>> In [1] it was identified that in ath10k_wmi_10_4_gen_tdls_peer_update()
>> the memset(skb->data, 0, sizeof(*cmd)) is unnecessary since function
>> ath10k_wmi_alloc_skb() already zeroes skb->data, so remove it.
> 
> Is .gen_tdls_peer_update only ever called after a fresh allocation? It
> wasn't obvious to me as I tried to follow the call paths. Is there harm
> in leaving this?

The only harm is a slight increase in code size and cpu cycles.

However note the skb allocation is done within
ath10k_wmi_10_4_gen_tdls_peer_update() itself, just before the code
being removed:
	skb = ath10k_wmi_alloc_skb(ar, len);
	if (!skb)
		return ERR_PTR(-ENOMEM);

And in ath10k_wmi_alloc_skb() we have:
	memset(skb->data, 0, round_len);

So the memset() being removed is always redundant.

/jeff