linux-kernel - Re: [greybus-dev] Re: [PATCH] greybus: Fix deref of NULL in __gb_lights_flash_brightness

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Message-ID: <m3wmqklkwk.fsf@gmail.com>
Date: Sat, 02 Mar 2024 15:21:15 +0000
From: Rui Miguel Silva <rmfrfs@...il.com>
To: Alex Elder <elder@...e.org>, Dan Carpenter <dan.carpenter@...aro.org>,
 Mikhail Lobanov <m.lobanov@...alinux.ru>
Cc: greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [greybus-dev] Re: [PATCH] greybus: Fix deref of NULL in
 __gb_lights_flash_brightness_set

Alex Elder <elder@...e.org> writes:
Hey Alex,

> On 3/2/24 3:59 AM, Dan Carpenter wrote:
>> On Fri, Mar 01, 2024 at 02:04:24PM -0500, Mikhail Lobanov wrote:
>>> Dereference of null pointer in the __gb_lights_flash_brightness_set function.
>>> Assigning the channel the result of executing the get_channel_from_mode function
>>> without checking for NULL may result in an error.
>> 
>> get_channel_from_mode() can only return NULL when light->channels_count
>> is zero.
>> 
>> Although get_channel_from_mode() seems buggy to me.  If it can't
>> find the correct mode, it just returns the last channel.  So potentially
>> it should be made to return NULL.
>
> I agree with you.  This looks quite wrong to me, and I
> like your fix, *except* there is also no need to check
> whether the channel pointer is null inside the loop.
> It's the address of an object, and will always be non-null.
>
>      static struct gb_channel *
>      get_channel_from_mode(struct gb_light *light, u32 mode)
>      {
>          struct gb_channel *channel;
>          u32 i;
>
>          for (i = 0; i < light->channels_count; i++) {
>              channel = &light->channels[i];
>              if (channel->mode == mode)
>                  return channel;
>          }
>          return NULL;
>      }
>
>
> Rui, could you please confirm what Dan says (and his
> proposed change) was your intention?

Yup, Dan is right.

>
> If so (and assuming you also fix the check for a null
> channel pointer inside the loop):

And you also here.
>
> Reviewed-by: Alex Elder <elder@...aro.org>

Thanks.

Cheers,
   Rui
>
> 					-Alex
>
>> 
>> diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
>> index d62f97249aca..acd435f5d25d 100644
>> --- a/drivers/staging/greybus/light.c
>> +++ b/drivers/staging/greybus/light.c
>> @@ -95,15 +95,15 @@ static struct led_classdev *get_channel_cdev(struct gb_channel *channel)
>>   static struct gb_channel *get_channel_from_mode(struct gb_light *light,
>>   						u32 mode)
>>   {
>> -	struct gb_channel *channel = NULL;
>> +	struct gb_channel *channel;
>>   	int i;
>>   
>>   	for (i = 0; i < light->channels_count; i++) {
>>   		channel = &light->channels[i];
>>   		if (channel && channel->mode == mode)
>> -			break;
>> +			return channel;
>>   	}
>> -	return channel;
>> +	return NULL;
>>   }
>>   
>>   static int __gb_lights_flash_intensity_set(struct gb_channel *channel,
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