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

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Date:   Thu, 30 Jul 2020 11:45:45 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Cengiz Can <cengiz@...nel.wtf>,
        "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 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.

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().

regards,
dan carpenter