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Date: Tue, 30 Apr 2024 14:00:57 -0700
From: Kees Cook <keescook@chromium.org>
To: Jeff Johnson <quic_jjohnson@quicinc.com>
Cc: Johannes Berg <johannes@sipsolutions.net>,
	Nathan Chancellor <nathan@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] wifi: nl80211: Avoid address calculations via out of
 bounds array indexing
Message-ID: <202404301358.CEA4B3D@keescook>
References: <20240424220057.work.819-kees@kernel.org>
 <e2f20484fb1f4607d099d2184c1d74c6a39febc1.camel@sipsolutions.net>
 <9983345a-d590-4a78-94ca-6d96832860b1@quicinc.com>
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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