[03/10] b43: Remove uninitialized_var() usage
diff mbox series

Message ID 20200603233203.1695403-4-keescook@chromium.org
State New
Headers show
Series
  • Remove uninitialized_var() macro
Related show

Commit Message

Kees Cook June 3, 2020, 11:31 p.m. UTC
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,
and make the (unreachable!) code do a conditional test.

[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/

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Comments

Nick Desaulniers June 4, 2020, 8:08 p.m. UTC | #1
On Wed, Jun 3, 2020 at 4:32 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,
> and make the (unreachable!) code do a conditional test.
>
> [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/
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
> index d3c001fa8eb4..88cdcea10d61 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)

The TODOs and `#if 0` in this function are concerning.  It looks like
`rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19.

Further, the loop has a case for `phy->rev >= 19` but we would have
returned earlier if that was the case.

>         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)
> @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
>                         pga_gain = (table[i] >> 24) & 0xf;
>                         pad_gain = (table[i] >> 19) & 0x1f;
>                         if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
> -                               rfpwr_offset = rf_pwr_offset_table[pad_gain];
> +                               rfpwr_offset = rf_pwr_offset_table
> +                                               ? rf_pwr_offset_table[pad_gain]
> +                                               : 0;
>                         else
> -                               rfpwr_offset = rf_pwr_offset_table[pga_gain];
> +                               rfpwr_offset = rf_pwr_offset_table
> +                                               ? rf_pwr_offset_table[pga_gain]
> +                                               : 0;


The code is trying to check `phy->rev >= 7 && phy->rev < 19` once
before the loop, then set `rf_pwr_offset_table`, so having another
conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm
ok with initializing it to `NULL`, but I'm not sure the conditional
check is necessary.  Do you get a compiler warning otherwise?

>                 } else {
>                         pga_gain = (table[i] >> 24) & 0xF;
>                         if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
> --
> 2.25.1
>
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Kees Cook June 4, 2020, 8:18 p.m. UTC | #2
On Thu, Jun 04, 2020 at 01:08:44PM -0700, Nick Desaulniers wrote:
> On Wed, Jun 3, 2020 at 4:32 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,
> > and make the (unreachable!) code do a conditional test.
> >
> > [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/
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
> > index d3c001fa8eb4..88cdcea10d61 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)
> 
> The TODOs and `#if 0` in this function are concerning.  It looks like
> `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19.
> 
> Further, the loop has a case for `phy->rev >= 19` but we would have
> returned earlier if that was the case.

Yeah, that's why I put the "(unreachable!)" note in the commit log. ;)

> 
> >         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)
> > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
> >                         pga_gain = (table[i] >> 24) & 0xf;
> >                         pad_gain = (table[i] >> 19) & 0x1f;
> >                         if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
> > -                               rfpwr_offset = rf_pwr_offset_table[pad_gain];
> > +                               rfpwr_offset = rf_pwr_offset_table
> > +                                               ? rf_pwr_offset_table[pad_gain]
> > +                                               : 0;
> >                         else
> > -                               rfpwr_offset = rf_pwr_offset_table[pga_gain];
> > +                               rfpwr_offset = rf_pwr_offset_table
> > +                                               ? rf_pwr_offset_table[pga_gain]
> > +                                               : 0;
> 
> 
> The code is trying to check `phy->rev >= 7 && phy->rev < 19` once
> before the loop, then set `rf_pwr_offset_table`, so having another
> conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm
> ok with initializing it to `NULL`, but I'm not sure the conditional
> check is necessary.  Do you get a compiler warning otherwise?

I mean, sort of the best thing to do is just remove nearly everything
here since it's actually unreachable. But it is commented as "when
supported ..." etc, so I figured I'd leave it. As part of that I didn't
want to leave any chance of a NULL deref, so I added the explicit tests
just for robustness.

*shrug*

-Kees
Nick Desaulniers June 4, 2020, 8:25 p.m. UTC | #3
On Thu, Jun 4, 2020 at 1:18 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Jun 04, 2020 at 01:08:44PM -0700, Nick Desaulniers wrote:
> > On Wed, Jun 3, 2020 at 4:32 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,
> > > and make the (unreachable!) code do a conditional test.
> > >
> > > [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/
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > ---
> > >  drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++---
> > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
> > > index d3c001fa8eb4..88cdcea10d61 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)
> >
> > The TODOs and `#if 0` in this function are concerning.  It looks like
> > `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19.
> >
> > Further, the loop has a case for `phy->rev >= 19` but we would have
> > returned earlier if that was the case.

oh, and there's an early return for `phy->rev < 3` I just noticed.

>
> Yeah, that's why I put the "(unreachable!)" note in the commit log. ;)

I don't think that note is correct.

>
> >
> > >         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)
> > > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
> > >                         pga_gain = (table[i] >> 24) & 0xf;
> > >                         pad_gain = (table[i] >> 19) & 0x1f;
> > >                         if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
> > > -                               rfpwr_offset = rf_pwr_offset_table[pad_gain];
> > > +                               rfpwr_offset = rf_pwr_offset_table
> > > +                                               ? rf_pwr_offset_table[pad_gain]
> > > +                                               : 0;
> > >                         else
> > > -                               rfpwr_offset = rf_pwr_offset_table[pga_gain];
> > > +                               rfpwr_offset = rf_pwr_offset_table
> > > +                                               ? rf_pwr_offset_table[pga_gain]
> > > +                                               : 0;
> >
> >
> > The code is trying to check `phy->rev >= 7 && phy->rev < 19` once
> > before the loop, then set `rf_pwr_offset_table`, so having another
> > conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm
> > ok with initializing it to `NULL`, but I'm not sure the conditional
> > check is necessary.  Do you get a compiler warning otherwise?
>
> I mean, sort of the best thing to do is just remove nearly everything
> here since it's actually unreachable. But it is commented as "when

This code is reachable. Consider `phy->rev >= 7 && phy->rev < 19`.  If
`rf_pwr_offset_table` was NULL, it would have returned early on L4246,
so the checks added in this patch are unnecessary.  Forgive me if
there's some other control flow I'm not considering.

> supported ..." etc, so I figured I'd leave it. As part of that I didn't
> want to leave any chance of a NULL deref, so I added the explicit tests
> just for robustness.
>
> *shrug*
Kalle Valo June 5, 2020, 9:20 a.m. UTC | #4
Kees Cook <keescook@chromium.org> writes:

> 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,
> and make the (unreachable!) code do a conditional test.
>
> [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/
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

[...]

> @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
>  			pga_gain = (table[i] >> 24) & 0xf;
>  			pad_gain = (table[i] >> 19) & 0x1f;
>  			if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
> -				rfpwr_offset = rf_pwr_offset_table[pad_gain];
> +				rfpwr_offset = rf_pwr_offset_table
> +						? rf_pwr_offset_table[pad_gain]
> +						: 0;
>  			else
> -				rfpwr_offset = rf_pwr_offset_table[pga_gain];
> +				rfpwr_offset = rf_pwr_offset_table
> +						? rf_pwr_offset_table[pga_gain]
> +						: 0;

To me this is ugly, isn't there a better way to fix this?

Patch
diff mbox series

diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
index d3c001fa8eb4..88cdcea10d61 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)
@@ -4256,9 +4256,13 @@  static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev)
 			pga_gain = (table[i] >> 24) & 0xf;
 			pad_gain = (table[i] >> 19) & 0x1f;
 			if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)
-				rfpwr_offset = rf_pwr_offset_table[pad_gain];
+				rfpwr_offset = rf_pwr_offset_table
+						? rf_pwr_offset_table[pad_gain]
+						: 0;
 			else
-				rfpwr_offset = rf_pwr_offset_table[pga_gain];
+				rfpwr_offset = rf_pwr_offset_table
+						? rf_pwr_offset_table[pga_gain]
+						: 0;
 		} else {
 			pga_gain = (table[i] >> 24) & 0xF;
 			if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ)