Subject: Re: [PATCH net] vhost_vdpa: Return -EFUALT if copy_from_user() fails

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 23 Oct 2020 11:34:25 -0400

On Fri, Oct 23, 2020 at 03:08:53PM +0300, Dan Carpenter wrote:
> The copy_to/from_user() functions return the number of bytes which we
> weren't able to copy but the ioctl should return -EFAULT if they fail.
> 
> Fixes: a127c5bbb6a8 ("vhost-vdpa: fix backend feature ioctls")
> Signed-off-by: Dan Carpenter <[email-masked]>

Acked-by: Michael S. Tsirkin <[email-masked]>
Needed for stable I guess.

> ---
>  drivers/vhost/vdpa.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 62a9bb0efc55..c94a97b6bd6d 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -428,12 +428,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  	void __user *argp = (void __user *)arg;
>  	u64 __user *featurep = argp;
>  	u64 features;
> -	long r;
> +	long r = 0;
>  
>  	if (cmd == VHOST_SET_BACKEND_FEATURES) {
> -		r = copy_from_user(&features, featurep, sizeof(features));
> -		if (r)
> -			return r;
> +		if (copy_from_user(&features, featurep, sizeof(features)))
> +			return -EFAULT;
>  		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
>  			return -EOPNOTSUPP;
>  		vhost_set_backend_features(&v->vdev, features);
> @@ -476,7 +475,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  		break;
>  	case VHOST_GET_BACKEND_FEATURES:
>  		features = VHOST_VDPA_BACKEND_FEATURES;
> -		r = copy_to_user(featurep, &features, sizeof(features));
> +		if (copy_to_user(featurep, &features, sizeof(features)))
> +			r = -EFAULT;
>  		break;
>  	default:
>  		r = vhost_dev_ioctl(&v->vdev, cmd, argp);