Re: [PATCH] greybus: lights: check return of get_channel_from_mode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Mar 25, 2024 at 01:31:34PM -0500, Alex Elder wrote:
> On 3/25/24 12:25 PM, Greg Kroah-Hartman wrote:
> > On Thu, Mar 07, 2024 at 09:48:13AM +0000, Rui Miguel Silva wrote:
> > > If channel for the given node is not found we return null from
> > > get_channel_from_mode. Make sure we validate the return pointer
> > > before using it in two of the missing places.
> > > 
> > > This was originally reported in [0]:
> > > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > > 
> > > [0] https://lore.kernel.org/all/20240301190425.120605-1-m.lobanov@rosalinux.ru
> > > 
> > > Fixes: 2870b52bae4c ("greybus: lights: add lights implementation")
> > > Reported-by: Mikhail Lobanov <m.lobanov@rosalinux.ru>
> > > Suggested-by: Mikhail Lobanov <m.lobanov@rosalinux.ru>
> > > Suggested-by: Alex Elder <elder@ieee.org>
> > > Signed-off-by: Rui Miguel Silva <rmfrfs@gmail.com>
> > > ---
> > >   drivers/staging/greybus/light.c | 6 +++++-
> > >   1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
> > > index c6bd86a5335a..6f10b9e2c053 100644
> > > --- a/drivers/staging/greybus/light.c
> > > +++ b/drivers/staging/greybus/light.c
> > > @@ -147,6 +147,9 @@ static int __gb_lights_flash_brightness_set(struct gb_channel *channel)
> > >   		channel = get_channel_from_mode(channel->light,
> > >   						GB_CHANNEL_MODE_TORCH);
> > > +	if (!channel)
> > > +		return -EINVAL;
> > > +
> > >   	/* For not flash we need to convert brightness to intensity */
> > >   	intensity = channel->intensity_uA.min +
> > >   			(channel->intensity_uA.step * channel->led->brightness);
> > > @@ -549,7 +552,8 @@ static int gb_lights_light_v4l2_register(struct gb_light *light)
> > >   	}
> > >   	channel_flash = get_channel_from_mode(light, GB_CHANNEL_MODE_FLASH);
> > > -	WARN_ON(!channel_flash);
> > > +	if (WARN_ON(!channel_flash))
> > > +		return -EINVAL;
> > 
> > We should NOT crash machines just because of this, the WARN_ON() should
> > be removed and just properly handle the error please.
> 
> Greg, WARN_ON() doesn't normally crash the machine.  That said,
> it's reasonable to remove the WARN_ON().

The huge majority of running Linux systems in the world run with
panic-on-warn enabled, including the one in your pocket :(

> I think the purpose of the warning is that this is a case that
> should "never happen," so if it does, it's making some noise.

Making noise by rebooting the box is not good.

thanks,

greg k-h