Linux Virtualization - Feb 2014 - [PATCH net] vhost_net: do not report a used len larger than receive buffer size

Currently, even if the packet were truncated by lower socket, we still
report the packet size as the used len which may confuse guest
driver. Fixes this by returning the size of guest receive buffer instead.

Fixes 3a4d5c94e959359ece6d6b55045c3f046677f55c
(vhost_net: a kernel-level virtio server)

Cc: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/net.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9a68409..06268a0 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -525,7 +525,8 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 		++headcount;
 		seg += in;
 	}
-	heads[headcount - 1].len += datalen;
+	if (likely(datalen < 0))
+		heads[headcount - 1].len += datalen;
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
-- 
1.8.3.2

On Wed, Feb 12, 2014 at 01:57:46PM +0800, Jason Wang
wrote:
> Currently, even if the packet were truncated by lower socket, we still
> report the packet size as the used len which may confuse guest
> driver. Fixes this by returning the size of guest receive buffer instead.
> 
> Fixes 3a4d5c94e959359ece6d6b55045c3f046677f55c
> (vhost_net: a kernel-level virtio server)
> 
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
As discussed off-line:

NAK

and a fixed version will be sent.
> ---
>  drivers/vhost/net.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 9a68409..06268a0 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -525,7 +525,8 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
>  		++headcount;
>  		seg += in;
>  	}
> -	heads[headcount - 1].len += datalen;
> +	if (likely(datalen < 0))
> +		heads[headcount - 1].len += datalen;
>  	*iovcount = seg;
>  	if (unlikely(log))
>  		*log_num = nlogs;
> -- 
> 1.8.3.2