Re: [greybus-dev] Re: [PATCH] greybus: Fix deref of NULL in __gb_lights_flash_brightness_set

[Alex Elder]

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?

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

Reviewed-by: Alex Elder <elder@xxxxxxxxxx>

					-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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