linux-kernel - Re: [PATCH v2] Input: usbtouchscreen

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Date:   Mon, 27 Jun 2022 09:46:27 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Input: usbtouchscreen - add driver_info sanity check

On Thu, Jun 23, 2022 at 08:59:52AM -0700, Dmitry Torokhov wrote:
> On Thu, Jun 23, 2022 at 08:24:46AM +0200, Johan Hovold wrote:
> > Add a sanity check on the device id-table driver_info field to make sure
> > we never access a type structure (and function pointers) outside of the
> > device info array (e.g. if someone fails to ifdef a device-id entry).
> > 
> > Note that this also suppresses a compiler warning with -Warray-bounds
> > (gcc-11.3.0) when compile-testing the driver without enabling any of
> > the device type Kconfig options:
> > 
> >     drivers/input/touchscreen/usbtouchscreen.c: In function 'usbtouch_probe':
> >     drivers/input/touchscreen/usbtouchscreen.c:1668:16:warning: array subscript <unknown> is outside array bounds of 'struct usbtouch_device_info[0]' [-Warray-bounds]
> >      1668 |         type = &usbtouch_dev_info[id->driver_info];
> > 
> > Signed-off-by: Johan Hovold <johan@...nel.org>
> > ---
> > 
> > Changes in v2
> >  - use ARRAY_SIZE() for the sanity check (Dmitry)
> >  - drop the dummy entry and combine the two patches as the sanity check
> >    itself is enough to suppress the compiler warning (Dmitry)
> >  - use -ENODEV instead of -EINVAL even if this means no error will be
> >    logged in the unlikely event of a future driver bug
> 
> Is this on purpose or because I happened to have used this error code
> when I suggested the change? I'm fine with returning -EINVAL there.

It was on purpose. Returning -EINVAL (invalid argument) here just
doesn't seem quite right. I skimmed the errno list for a better
alternative, but decided -ENODEV works as well.

If there's ever a driver bug that triggers this, you could say the
device isn't supported in that configuration. ;)

If you prefer -EINVAL, I'll change it back.

Johan