netdev - Re: [PATCH v2 44/63] mac80211: Use memset

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Message-ID: <202108180203.592E3F01@keescook>
Date:   Wed, 18 Aug 2021 02:05:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        dri-devel@...ts.freedesktop.org, linux-staging@...ts.linux.dev,
        linux-block@...r.kernel.org, linux-kbuild@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 44/63] mac80211: Use memset_after() to clear tx status

On Wed, Aug 18, 2021 at 10:06:51AM +0200, Johannes Berg wrote:
> On Wed, 2021-08-18 at 09:08 +0200, Johannes Berg wrote:
> > On Tue, 2021-08-17 at 23:05 -0700, Kees Cook wrote:
> > > 
> > > @@ -275,12 +275,11 @@ static void carl9170_tx_release(struct kref *ref)
> > >  	if (WARN_ON_ONCE(!ar))
> > >  		return;
> > >  
> > > 
> > > 
> > > 
> > > -	BUILD_BUG_ON(
> > > -	    offsetof(struct ieee80211_tx_info, status.ack_signal) != 20);
> > > -
> > > -	memset(&txinfo->status.ack_signal, 0,
> > > -	       sizeof(struct ieee80211_tx_info) -
> > > -	       offsetof(struct ieee80211_tx_info, status.ack_signal));
> > > +	/*
> > > +	 * Should this call ieee80211_tx_info_clear_status() instead of clearing
> > > +	 * manually? txinfo->status.rates do not seem to be used here.
> > > +	 */
> > 
> > Since you insist, I went digging :)
> > 
> > It should not, carl9170_tx_fill_rateinfo() has filled the rate
> > information before we get to this point.

Ah-ha! Thanks for checking. I'll update the comment to explain the
rationale here.

> Otherwise, looks fine, FWIW.

Thanks!

> Are you going to apply all of these together somewhere? I (we) can't,
> since memset_after() doesn't exist yet.

Right, given the dependencies, I am expecting to just carry the whole
series, since the vast majority of it has no binary changes, etc. I'm
hoping to get it into -next soon, but we're uncomfortably close to the
merge window. :P

-- 
Kees Cook