linux-kernel - Re: [PATCH] media: em28xx: fix function pointer check

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Date:   Wed, 9 Sep 2020 16:28:06 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     trix@...hat.com, mchehab@...nel.org, natechancellor@...il.com,
        ndesaulniers@...gle.com, brad@...tdimension.cc, mkrufky@...uxtv.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] media: em28xx: fix function pointer check

On 03/09/2020 16:50, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> clang static analyzer reports this problem
> 
> em28xx-core.c:1162:4: warning: Called function pointer
>   is null (null dereference)
>         ops->suspend(dev->dev_next);
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This is the problem block
> 
> 	if (ops->suspend)
> 		ops->suspend(dev);
> 	if (dev->dev_next)
> 		ops->suspend(dev->dev_next);
> 
> The check for ops->suspend only covers one statement.
> So fix the check consistent with other similar in
> the file.
> 
> Change a similar check in em28xx_resume_extension()
> to use consistent logic as its siblings.
> 
> Fixes: be7fd3c3a8c5 ("media: em28xx: Hauppauge DualHD second tuner functionality")
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/media/usb/em28xx/em28xx-core.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c
> index e6088b5d1b80..d60f4c2a661d 100644
> --- a/drivers/media/usb/em28xx/em28xx-core.c
> +++ b/drivers/media/usb/em28xx/em28xx-core.c
> @@ -1156,10 +1156,11 @@ int em28xx_suspend_extension(struct em28xx *dev)
>  	dev_info(&dev->intf->dev, "Suspending extensions\n");
>  	mutex_lock(&em28xx_devlist_mutex);
>  	list_for_each_entry(ops, &em28xx_extension_devlist, next) {
> -		if (ops->suspend)
> +		if (ops->suspend) {
>  			ops->suspend(dev);
> -		if (dev->dev_next)
> -			ops->suspend(dev->dev_next);
> +			if (dev->dev_next)
> +				ops->suspend(dev->dev_next);
> +		}
>  	}
>  	mutex_unlock(&em28xx_devlist_mutex);
>  	return 0;
> @@ -1172,11 +1173,11 @@ int em28xx_resume_extension(struct em28xx *dev)
>  	dev_info(&dev->intf->dev, "Resuming extensions\n");
>  	mutex_lock(&em28xx_devlist_mutex);
>  	list_for_each_entry(ops, &em28xx_extension_devlist, next) {
> -		if (!ops->resume)
> -			continue;

Actually, this code is fine: if !ops->resume, then just continue.

So there is no need to change this resume code.

And in fact, I think it would be best if the same approach was used in
em28xx_suspend_extension.

Regards,

	Hans

> -		ops->resume(dev);
> -		if (dev->dev_next)
> -			ops->resume(dev->dev_next);
> +		if (ops->resume) {
> +			ops->resume(dev);
> +			if (dev->dev_next)
> +				ops->resume(dev->dev_next);
> +		}
>  	}
>  	mutex_unlock(&em28xx_devlist_mutex);
>  	return 0;
>