linux-kernel - Re: [PATCH] staging: atomisp: move null check to earlier point

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Date:   Thu, 30 Jul 2020 11:59:10 +0300
From:   Cengiz Can <cengiz@...nel.wtf>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
CC:     "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH] staging: atomisp: move null check to earlier point



On July 30, 2020 11:48:06 Dan Carpenter <dan.carpenter@...cle.com> wrote:

> On Wed, Jul 29, 2020 at 06:13:44PM +0300, Andy Shevchenko wrote:
>> On Wed, Jul 29, 2020 at 5:00 PM Cengiz Can <cengiz@...nel.wtf> wrote:
>>>
>>> `find_gmin_subdev` function that returns a pointer to `struct
>>> gmin_subdev` can return NULL.
>>>
>>> In `gmin_v2p8_ctrl` there's a call to this function but the possibility
>>> of a NULL was not checked before its being dereferenced. ie:
>>>
>>> ```
>>> /* Acquired here --------v */
>>> struct gmin_subdev *gs = find_gmin_subdev(subdev);
>>> int ret;
>>> int value;
>>>
>>> /*  v------Dereferenced here */
>>> if (gs->v2p8_gpio >= 0) {
>>>  pr_info("atomisp_gmin_platform: 2.8v power on GPIO %d\n",
>>>          gs->v2p8_gpio);
>>>  ret = gpio_request(gs->v2p8_gpio, "camera_v2p8");
>>>  if (!ret)
>>>          ret = gpio_direction_output(gs->v2p8_gpio, 0);
>>>  if (ret)
>>>          pr_err("V2P8 GPIO initialization failed\n");
>>> }
>>> ```
>>>
>>> I have moved the NULL check before deref point.
>>
>> "Move the NULL check..."
>> See Submitting Patches documentation how to avoid "This patch", "I", "we", etc.

Noted. Sorry. I'm not a native English speaker.

>>
>
> I always feel like this is a pointless requirement.  We're turning into
> bureaucracts.
>
>>
>>> diff --git a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c 
>>> b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
>>> index 0df46a1af5f0..8e9c5016f299 100644
>>> --- a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
>>> +++ b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
>>> @@ -871,6 +871,11 @@ static int gmin_v2p8_ctrl(struct v4l2_subdev *subdev, 
>>> int on)
>>>  int ret;
>>>  int value;
>>>
>>> +       if (!gs) {
>>> +               pr_err("Unable to find gmin subdevice\n");
>>
>>> +               return -EINVAL;
>>
>> And here is a change of semantics...
>
> Yeah.  The change of semantics should be documented in the commit
> message, but it's actually correct.  I discussed this with Mauro earlier
> but my bug reporting script didn't CC a mailing list and I didn't
> catch it.  Mauro suggested:
>
>    53  > Yet, it could make sense to have something like:
>    54  >
>    55  >       if (WARN_ON(!gs))
>    56  >               return -ENODEV;
>    57  >
>    58  > at the beginning of the functions that call find_gmin_subdev().

I will be updating v2 according to this.

>
> regards,
> dan carpenter