linux-kernel - Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it on dev

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Message-ID: <55E5803F.3090704@canonical.com>
Date:	Tue, 01 Sep 2015 11:38:55 +0100
From:	Colin Ian King <colin.king@...onical.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Geoff Levand <geoff@...radead.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ps3-vuart: BUG_ON on null drv before dereferencing it
 on dev_dbg

On 01/09/15 11:35, Geert Uytterhoeven wrote:
> Hi Colin,
> 
> On Tue, Sep 1, 2015 at 12:21 PM, Colin King <colin.king@...onical.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@...onical.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@...ux-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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