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

Rui Miguel Silva
2024-03-25T19:08:55Z

Hey Alex,

Alex Elder <elder@ieee.org> writes:

> 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.

I also lost track of all this failure cascade options that normally
take the all system down.

Thanks anyway for the comments,
Cheers,
Rui

>
> -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