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

Alex Elder
2024-03-02T14:57:19Z

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@linaro.org>

-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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