linux-kernel - Re: [PATCH v2 04/16] b43: Remove uninitialized

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Message-ID: <202006221403.EEAD37E94B@keescook>
Date:   Mon, 22 Jun 2020 14:04:04 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org,
        Network Development <netdev@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        linux-ide@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-spi@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2 04/16] b43: Remove uninitialized_var() usage

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@...omium.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@...omium.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.

-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