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

Rui Miguel Silva
2024-03-02T15:21:17Z

Alex Elder <elder@ieee.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@linaro.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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