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

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Date: Sat, 02 Mar 2024 15:18:13 +0000
From: Rui Miguel Silva <rmfrfs@...il.com>
To: Mikhail Lobanov <m.lobanov@...alinux.ru>
Cc: Mikhail Lobanov <m.lobanov@...alinux.ru>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, greybus-dev@...ts.linaro.org,
 linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] greybus: Fix deref of NULL in
 __gb_lights_flash_brightness_set

Hi Mikhail,
Thanks for your patch.

Mikhail Lobanov <m.lobanov@...alinux.ru> writes:

> 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.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 2870b52bae4c ("greybus: lights: add lights implementation")
> Signed-off-by: Mikhail Lobanov <m.lobanov@...alinux.ru>

Yeah, at the time when this was implemented I recall that we could only
set the brightness of the torch mode in a flash led, not in the flash
only mode. So, if we were getting here was that for sure we had a torch
channel and get_channel_from_mode will always find a channel, so never
returning null here.

but yeah, this is safer. but maybe just do something like the bellow
would be simpler:
modified   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);

what do you think?

Cheers,
    Rui

> ---
>  drivers/staging/greybus/light.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
> index 87d36948c610..929514350947 100644
> --- a/drivers/staging/greybus/light.c
> +++ b/drivers/staging/greybus/light.c
> @@ -148,10 +148,15 @@ static int __gb_lights_flash_brightness_set(struct gb_channel *channel)
>  						GB_CHANNEL_MODE_TORCH);
>  
>  	/* For not flash we need to convert brightness to intensity */
> -	intensity = channel->intensity_uA.min +
> +
> +	if (channel) {
> +		intensity = channel->intensity_uA.min +
>  			(channel->intensity_uA.step * channel->led->brightness);
>  
> -	return __gb_lights_flash_intensity_set(channel, intensity);
> +		return __gb_lights_flash_intensity_set(channel, intensity);
> +	}
> +
> +	return 0;
>  }
>  #else
>  static struct gb_channel *get_channel_from_cdev(struct led_classdev *cdev)
> -- 
> 2.43.0