Subject: Re: [PATCH] nfc: Allow to create multiple virtual nci devices

From: Leon Romanovsky <[email-masked]>
Date: Mon, 31 Oct 2022 11:23:40 +0200

On Sun, Oct 30, 2022 at 03:29:19PM +0100, Dmitry Vyukov wrote:
> The current virtual nci driver is great for testing and fuzzing.
> But it allows to create at most one "global" device which does not allow
> to run parallel tests and harms fuzzing isolation and reproducibility.
> Restructure the driver to allow creation of multiple independent devices.
> This should be backwards compatible for existing tests.
> 
> Signed-off-by: Dmitry Vyukov <[email-masked]>
> Cc: Bongsu Jeon <[email-masked]>
> Cc: Krzysztof Kozlowski <[email-masked]>
> Cc: [email-masked]
> ---
>  drivers/nfc/virtual_ncidev.c | 143 ++++++++++++++++-------------------
>  1 file changed, 66 insertions(+), 77 deletions(-)

<...>

>  static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
>  {
> -	mutex_lock(&nci_mutex);
> -	if (state != virtual_ncidev_enabled) {
> -		mutex_unlock(&nci_mutex);
> -		kfree_skb(skb);
> -		return 0;
> -	}
> +	struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>  
> -	if (send_buff) {
> -		mutex_unlock(&nci_mutex);
> +	mutex_lock(&vdev->mtx);
> +	if (vdev->send_buff) {
> +		mutex_unlock(&vdev->mtx);
>  		kfree_skb(skb);

You probably need to set vdev->send_buff to NULL here.

>  		return -1;
>  	}
> -	send_buff = skb_copy(skb, GFP_KERNEL);
> -	mutex_unlock(&nci_mutex);
> -	wake_up_interruptible(&wq);
> +	vdev->send_buff = skb_copy(skb, GFP_KERNEL);

You don't check return value of skb_copy(), it can fail, but
this function will return 0 (success). Do you do it deliberately?

If yes, please add a comment to the code, as it is not clear.

Thanks

> +	mutex_unlock(&vdev->mtx);
> +	wake_up_interruptible(&vdev->wq);
>  	consume_skb(skb);
>  
>  	return 0;