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

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Date: Tue, 30 Apr 2024 12:01:44 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Kees Cook <keescook@...omium.org>
Cc: 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, Jeff Johnson
 <quic_jjohnson@...cinc.com>, "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 Wed, 2024-04-24 at 15:01 -0700, Kees Cook wrote:
> Before request->channels[] can be used, request->n_channels must be set.
> Additionally, address calculations for memory after the "channels" array
> need to be calculated from the allocation base ("request") rather than
> via the first "out of bounds" index of "channels", otherwise run-time
> bounds checking will throw a warning.
> 
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Fixes: e3eac9f32ec0 ("wifi: cfg80211: Annotate struct cfg80211_scan_request with __counted_by")

While I was weighing whether or not to apply this for 6.9 still ...

> +	request->n_channels = n_channels;
>  
>  	if (n_ssids)
> -		request->ssids = (void *)&request->channels[n_channels];
> +		request->ssids = (void *)request + ssids_offset;

This really doesn't even seem right, shouldn't do pointer arithmetic on
void pointers. Same applies below too.

And also if you set n_channels before, perhaps it's actually OK to get a
pointer to *after*? Not sure though.

johannes