Re: [PATCH v2 04/16] b43: Remove uninitialized_var() usage

From: Nick Desaulniers <ndesaulniers@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Joe Perches <joe@perches.com>, Andy Whitcroft <apw@canonical.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	drbd-dev@lists.linbit.com, linux-block@vger.kernel.org,
	b43-dev@lists.infradead.org,
	Network Development <netdev@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	linux-ide@vger.kernel.org, linux-clk@vger.kernel.org,
	linux-spi@vger.kernel.org,
	Linux Memory Management List <linux-mm@kvack.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH v2 04/16] b43: Remove uninitialized_var() usage
Date: Tue, 23 Jun 2020 11:29:38 -0700	[thread overview]
Message-ID: <CAKwvOdmr0dmC7UtL9Qcgm9Ue_Q2mhKzYiHcXpaB=LpMKpYeYqA@mail.gmail.com> (raw)
In-Reply-To: <202006221403.EEAD37E94B@keescook>

On Mon, Jun 22, 2020 at 2:04 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Jun 22, 2020 at 10:04:18AM -0700, Nick Desaulniers wrote:
> > On Fri, Jun 19, 2020 at 8:30 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > > "unused variable"). If the compiler thinks it is uninitialized, either
> > > simply initialize the variable or make compiler changes. As a precursor
> > > to removing[2] this[3] macro[4], just initialize this variable to NULL.
> > > No later NULL deref is possible due to the early returns outside of the
> > > (phy->rev >= 7 && phy->rev < 19) case, which explicitly tests for NULL.
> > >
> > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> > >
> > > Fixes: 58619b14d106 ("b43: move under broadcom vendor directory")
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > I see three total uses of uninitialized_var() in this file, do we want
> > to eliminate all of them?
>
> This is the only one that needed an explicit initialization -- all the
> others are handled in the treewide patch. I *could* split it out here,
> but I found it easier to keep the "no op" changes together in the
> treewide patch.

Ah, got it.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> -Kees
>
> >
> > > ---
> > >  drivers/net/wireless/broadcom/b43/phy_n.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
> > > index c33b4235839d..46db91846007 100644
> > > --- a/drivers/net/wireless/broadcom/b43/phy_n.c
> > > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c
> > > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
> > >         u32 rfpwr_offset;
> > >         u8 pga_gain, pad_gain;
> > >         int i;
> > > -       const s16 *uninitialized_var(rf_pwr_offset_table);
> > > +       const s16 *rf_pwr_offset_table = NULL;
> > >
> > >         table = b43_nphy_get_tx_gain_table(dev);
> > >         if (!table)
> > > --
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
>
> --
> Kees Cook

-- 
Thanks,
~Nick Desaulniers