Subject: Re: [PATCH net V2] vhost: correctly remove wait queue during poll failure

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 29 Mar 2018 07:20:30 +0300

On Tue, Mar 27, 2018 at 08:50:52PM +0800, Jason Wang wrote:
> We tried to remove vq poll from wait queue, but do not check whether
> or not it was in a list before. This will lead double free. Fixing
> this by switching to use vhost_poll_stop() which zeros poll->wqh after
> removing poll from waitqueue to make sure it won't be freed twice.
> 
> Cc: Darren Kenny <[email-masked]>
> Reported-by: [email-masked]
> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting backend")
> Signed-off-by: Jason Wang <[email-masked]>

OK with this the only bug we have is where get user pages returns 0
(Reported-by: [email-masked])

> ---
> Changes from V1:
> - tweak the commit log for to match the code
> ---
>  drivers/vhost/vhost.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 1b3e8d2d..5d5a9d9 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file)
>  	if (mask)
>  		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
>  	if (mask & EPOLLERR) {
> -		if (poll->wqh)
> -			remove_wait_queue(poll->wqh, &poll->wait);
> +		vhost_poll_stop(poll);
>  		ret = -EINVAL;
>  	}
>  
> -- 
> 2.7.4