linux-kernel - Re: [PATCH 5/6] vhost_net: poll vhost queue after marking DMA is done

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130816100055.GC21821@redhat.com>
Date:	Fri, 16 Aug 2013 13:00:55 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] vhost_net: poll vhost queue after marking DMA is done

On Fri, Aug 16, 2013 at 01:16:29PM +0800, Jason Wang wrote:
> We used to poll vhost queue before making DMA is done, this is racy if vhost
> thread were waked up before marking DMA is done which can result the signal to
> be missed. Fix this by always poll the vhost thread before DMA is done.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Indeed, but vhost_net_ubuf_put should be the last thing we do:
it can cause the device to go away and we'll get
a user after free.

> ---
>  drivers/vhost/net.c |    9 +++++----
>  1 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 70cab75..a035a89 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -308,6 +308,11 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
>  	struct vhost_virtqueue *vq = ubufs->vq;
>  	int cnt = atomic_read(&ubufs->kref.refcount);
>  
> +	/* set len to mark this desc buffers done DMA */
> +	vq->heads[ubuf->desc].len = success ?
> +		VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
> +	vhost_net_ubuf_put(ubufs);
> +
>  	/*
>  	 * Trigger polling thread if guest stopped submitting new buffers:
>  	 * in this case, the refcount after decrement will eventually reach 1
> @@ -318,10 +323,6 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
>  	 */
>  	if (cnt <= 2 || !(cnt % 16))
>  		vhost_poll_queue(&vq->poll);
> -	/* set len to mark this desc buffers done DMA */
> -	vq->heads[ubuf->desc].len = success ?
> -		VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN;
> -	vhost_net_ubuf_put(ubufs);
>  }
>  
>  /* Expects to be always run from workqueue - which acts as
> -- 
> 1.7.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/