Re: [Xen-devel] [PATCH 6/6] xen-netback: don't disconnect frontend when seeing oversize frame

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Mar 25, 2013 at 11:08:22AM +0000, Wei Liu wrote:
> Some buggy frontends may generate frames larger than 64 KiB. We should
> aggresively consume all slots and drop the packet instead of disconnecting the
> frontend.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>

CC stable@vger.kernel.org ?

> ---
>  drivers/net/xen-netback/netback.c |   32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index a634dc5..1971623 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -924,10 +924,12 @@ static void netbk_fatal_tx_err(struct xenvif *vif)
>  static int netbk_count_requests(struct xenvif *vif,
>  				struct xen_netif_tx_request *first,
>  				struct xen_netif_tx_request *txp,
> -				int work_to_do)
> +				int work_to_do,
> +				RING_IDX first_idx)
>  {
>  	RING_IDX cons = vif->tx.req_cons;
>  	int slots = 0;
> +	bool drop = false;
>  
>  	if (!(first->flags & XEN_NETTXF_more_data))
>  		return 0;
> @@ -947,10 +949,21 @@ static int netbk_count_requests(struct xenvif *vif,
>  
>  		memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
>  		       sizeof(*txp));
> -		if (txp->size > first->size) {
> -			netdev_err(vif->dev, "Packet is bigger than frame.\n");
> -			netbk_fatal_tx_err(vif);
> -			return -EIO;
> +
> +		/* If the guest submitted a frame >= 64 KiB then
> +		 * first->size overflowed and following slots will
> +		 * appear to be larger than the frame.
> +		 *
> +		 * This cannot be fatal error as there are buggy
> +		 * frontends that do this.
> +		 *
> +		 * Consume all slots and drop the packet.
> +		 */
> +		if (!drop && txp->size > first->size) {
> +			if (net_ratelimit())
> +				netdev_dbg(vif->dev,
> +					   "Packet is bigger than frame.\n");
> +			drop = true;
>  		}
>  
>  		first->size -= txp->size;
> @@ -963,6 +976,12 @@ static int netbk_count_requests(struct xenvif *vif,
>  			return -EINVAL;
>  		}
>  	} while ((txp++)->flags & XEN_NETTXF_more_data);
> +
> +	if (drop) {
> +		netbk_tx_err(vif, first, first_idx + slots);
> +		return -EIO;
> +	}
> +
>  	return slots;
>  }
>  
> @@ -1429,7 +1448,8 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk *netbk)
>  				continue;
>  		}
>  
> -		ret = netbk_count_requests(vif, &txreq, txfrags, work_to_do);
> +		ret = netbk_count_requests(vif, &txreq, txfrags,
> +					   work_to_do, idx);
>  		if (unlikely(ret < 0))
>  			continue;
>  
> -- 
> 1.7.10.4
> 
> 
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