netdev - [PATCH net 3/3] xen-netback: BUG_ON in xenvif_rx

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Date:	Thu, 27 Mar 2014 12:23:08 +0000
From:	Paul Durrant <paul.durrant@...rix.com>
To:	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>
CC:	Paul Durrant <paul.durrant@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Sander Eikelenboom <linux@...elenboom.it>
Subject: [PATCH net 3/3] xen-netback: BUG_ON in xenvif_rx_action() not catching overflow

The BUG_ON to catch ring overflow in xenvif_rx_action() makes the assumption
that meta_slots_used == ring slots used. This is not the case for GSO
packets. This patch changes the test to actually check ring slots.

Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
Cc: Ian Campbell <ian.campbell@...rix.com>
Cc: Wei Liu <wei.liu2@...rix.com>
Cc: Sander Eikelenboom <linux@...elenboom.it>
---
 drivers/net/xen-netback/netback.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index ac35489..ae7351f 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -481,6 +481,8 @@ static void xenvif_rx_action(struct xenvif *vif)
 
 	while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
 		RING_IDX max_slots_needed;
+		RING_IDX old_req_cons;
+		RING_IDX ring_slots_used;
 		int i;
 
 		/* We need a cheap worse case estimate for the number of
@@ -520,8 +522,12 @@ static void xenvif_rx_action(struct xenvif *vif)
 			vif->rx_last_skb_slots = 0;
 
 		sco = (struct skb_cb_overlay *)skb->cb;
+
+		old_req_cons = vif->rx.req_cons;
 		sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
-		BUG_ON(sco->meta_slots_used > max_slots_needed);
+		ring_slots_used = vif->rx.req_cons - old_req_cons;
+
+		BUG_ON(ring_slots_used > max_slots_needed);
 
 		__skb_queue_tail(&rxq, skb);
 	}
-- 
1.7.10.4

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