Re: [PATCH] vringh: fix __vringh_iov() when riov and wiov are different

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 08, 2020 at 06:13:11PM +0200, Stefano Garzarella wrote:
> If riov and wiov are both defined and they point to different
> objects, only riov is initialized. If the wiov is not initialized
> by the caller, the function fails returning -EINVAL and printing
> "Readable desc 0x... after writable" error message.
> 
> Let's replace the 'else if' clause with 'if' to initialize both
> riov and wiov if they are not NULL.
> 
> As checkpatch pointed out, we also avoid crashing the kernel
> when riov and wiov are both NULL, replacing BUG() with WARN_ON()
> and returning -EINVAL.
> 
> Fixes: f87d0fbb5798 ("vringh: host-side implementation of virtio rings.")
> Cc: stable@vger.kernel.org
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Can you add more detail please? when does this trigger?

> ---
>  drivers/vhost/vringh.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index e059a9a47cdf..8bd8b403f087 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -284,13 +284,14 @@ __vringh_iov(struct vringh *vrh, u16 i,
>  	desc_max = vrh->vring.num;
>  	up_next = -1;
>  
> +	/* You must want something! */
> +	if (WARN_ON(!riov && !wiov))
> +		return -EINVAL;
> +
>  	if (riov)
>  		riov->i = riov->used = 0;
> -	else if (wiov)
> +	if (wiov)
>  		wiov->i = wiov->used = 0;
> -	else
> -		/* You must want something! */
> -		BUG();
>  
>  	for (;;) {
>  		void *addr;
> -- 
> 2.26.2