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

Alex Elder
2024-03-25T18:55:38Z

On 3/25/24 1:50 PM, Greg Kroah-Hartman wrote:
> 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 did not know that. Then WARN_ON() is no better than BUG_ON().
I'm still learning. Thank you.

-Alex

>> 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