linux-kernel - Re: [PATCH] wifi: nl80211: Avoid address calculations via out of bounds array indexing

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Date: Tue, 30 Apr 2024 14:00:57 -0700
From: Kees Cook <keescook@...omium.org>
To: Jeff Johnson <quic_jjohnson@...cinc.com>
Cc: Johannes Berg <johannes@...solutions.net>,
	Nathan Chancellor <nathan@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] wifi: nl80211: Avoid address calculations via out of
 bounds array indexing

On Tue, Apr 30, 2024 at 12:59:57PM -0700, Jeff Johnson wrote:
> On 4/30/2024 3:01 AM, Johannes Berg wrote:
> > This really doesn't even seem right, shouldn't do pointer arithmetic on
> > void pointers.
> 
> FWIW I argued this in the past in another context and Linus gave his opinion:
> 
> https://lore.kernel.org/all/CAHk-=whFKYMrF6euVvziW+drw7-yi1pYdf=uccnzJ8k09DoTXA@mail.gmail.com/

I was going to make the same argument. :) For this case, (void *) is
superior because we need to perform byte-granular arithmetic and we need
to use the implicit cast to the assigned variable's type.

The reason not to use the channels[] array is because we're not addressing
anything in the array -- we're addressing past it. Better to use the
correct allocation base.

-Kees

-- 
Kees Cook