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


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