[PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

On the unlikely event that drv is null, the current code will
perform a null pointer dereference with it when printing a dev_dbg
message.  Instead, the BUG_ON check on drv should be performed
before we emit the dev_dbg message.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/ps3/ps3-vuart.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/ps3/ps3-vuart.c b/drivers/ps3/ps3-vuart.c
index d6db822..632701a 100644
--- a/drivers/ps3/ps3-vuart.c
+++ b/drivers/ps3/ps3-vuart.c
@@ -1000,12 +1000,11 @@ static int ps3_vuart_probe(struct ps3_system_bus_device *dev)
 	dev_dbg(&dev->core, "%s:%d\n", __func__, __LINE__);
 
 	drv = ps3_system_bus_dev_to_vuart_drv(dev);
+	BUG_ON(!drv);
 
 	dev_dbg(&dev->core, "%s:%d: (%s)\n", __func__, __LINE__,
 		drv->core.core.name);
 
-	BUG_ON(!drv);
-
 	if (dev->port_number >= PORT_COUNT) {
 		BUG();
 		return -EINVAL;
-- 
2.5.0

Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[Geert Uytterhoeven]

Hi Colin,

On Tue, Sep 1, 2015 at 12:21 PM, Colin King <colin.king@canonical.com> wrote:
> On the unlikely event that drv is null, the current code will
> perform a null pointer dereference with it when printing a dev_dbg
> message.  Instead, the BUG_ON check on drv should be performed
> before we emit the dev_dbg message.

What about just removing the BUG_ON()?

The system will crash anyway, providing a backtrace.

> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/ps3/ps3-vuart.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/ps3/ps3-vuart.c b/drivers/ps3/ps3-vuart.c
> index d6db822..632701a 100644
> --- a/drivers/ps3/ps3-vuart.c
> +++ b/drivers/ps3/ps3-vuart.c
> @@ -1000,12 +1000,11 @@ static int ps3_vuart_probe(struct ps3_system_bus_device *dev)
>         dev_dbg(&dev->core, "%s:%d\n", __func__, __LINE__);
>
>         drv = ps3_system_bus_dev_to_vuart_drv(dev);
> +       BUG_ON(!drv);
>
>         dev_dbg(&dev->core, "%s:%d: (%s)\n", __func__, __LINE__,
>                 drv->core.core.name);
>
> -       BUG_ON(!drv);
> -
>         if (dev->port_number >= PORT_COUNT) {
>                 BUG();
>                 return -EINVAL;


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[Colin Ian King]

On 01/09/15 11:35, Geert Uytterhoeven wrote:
> Hi Colin,
> 
> On Tue, Sep 1, 2015 at 12:21 PM, Colin King <colin.king@canonical.com> wrote:
>> On the unlikely event that drv is null, the current code will
>> perform a null pointer dereference with it when printing a dev_dbg
>> message.  Instead, the BUG_ON check on drv should be performed
>> before we emit the dev_dbg message.
> 
> What about just removing the BUG_ON()?
> 
> The system will crash anyway, providing a backtrace.

I personally think a BUG_ON() shows intention to try to catch an
unexpected issue in a standard way as opposed to just removing it and
then hitting an issue with a null ptr deference.

> 
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>>  drivers/ps3/ps3-vuart.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/ps3/ps3-vuart.c b/drivers/ps3/ps3-vuart.c
>> index d6db822..632701a 100644
>> --- a/drivers/ps3/ps3-vuart.c
>> +++ b/drivers/ps3/ps3-vuart.c
>> @@ -1000,12 +1000,11 @@ static int ps3_vuart_probe(struct ps3_system_bus_device *dev)
>>         dev_dbg(&dev->core, "%s:%d\n", __func__, __LINE__);
>>
>>         drv = ps3_system_bus_dev_to_vuart_drv(dev);
>> +       BUG_ON(!drv);
>>
>>         dev_dbg(&dev->core, "%s:%d: (%s)\n", __func__, __LINE__,
>>                 drv->core.core.name);
>>
>> -       BUG_ON(!drv);
>> -
>>         if (dev->port_number >= PORT_COUNT) {
>>                 BUG();
>>                 return -EINVAL;
> 
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
> 

Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[Geert Uytterhoeven]

Hi Colin,

On Tue, Sep 1, 2015 at 12:38 PM, Colin Ian King
<colin.king@canonical.com> wrote:
> On 01/09/15 11:35, Geert Uytterhoeven wrote:
>> On Tue, Sep 1, 2015 at 12:21 PM, Colin King <colin.king@canonical.com> wrote:
>>> On the unlikely event that drv is null, the current code will
>>> perform a null pointer dereference with it when printing a dev_dbg
>>> message.  Instead, the BUG_ON check on drv should be performed
>>> before we emit the dev_dbg message.
>>
>> What about just removing the BUG_ON()?
>>
>> The system will crash anyway, providing a backtrace.
>
> I personally think a BUG_ON() shows intention to try to catch an
> unexpected issue in a standard way as opposed to just removing it and
> then hitting an issue with a null ptr deference.

I think this BUG_ON() was purely used during development of the ps3_vuart
framework.

Note that the corresponding platform_drv_probe() also just dereferences its
driver pointer.

>>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>>> ---
>>>  drivers/ps3/ps3-vuart.c | 3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/ps3/ps3-vuart.c b/drivers/ps3/ps3-vuart.c
>>> index d6db822..632701a 100644
>>> --- a/drivers/ps3/ps3-vuart.c
>>> +++ b/drivers/ps3/ps3-vuart.c
>>> @@ -1000,12 +1000,11 @@ static int ps3_vuart_probe(struct ps3_system_bus_device *dev)
>>>         dev_dbg(&dev->core, "%s:%d\n", __func__, __LINE__);
>>>
>>>         drv = ps3_system_bus_dev_to_vuart_drv(dev);
>>> +       BUG_ON(!drv);
>>>
>>>         dev_dbg(&dev->core, "%s:%d: (%s)\n", __func__, __LINE__,
>>>                 drv->core.core.name);
>>>
>>> -       BUG_ON(!drv);
>>> -
>>>         if (dev->port_number >= PORT_COUNT) {
>>>                 BUG();
>>>                 return -EINVAL;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev_dbg

[Geoff Levand]

On Tue, 2015-09-01 at 11:21 +0100, Colin King wrote:
> On the unlikely event that drv is null, the current code will
> perform a null pointer dereference with it when printing a dev_dbg
> message.  Instead, the BUG_ON check on drv should be performed
> before we emit the dev_dbg message.
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

I applied this to my ps3-linux repo.  I can update it if you decide to
do the other fixes Geert mentioned.

-Geoff