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 necessarily the case
for GSO packets, because the non-prefix GSO protocol consumes one more ring
slot than meta-slot for the 'extra_info'. This patch changes the test to
actually check ring slots.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 573f3e81e5d2..cd0bd95ccc14 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -482,6 +482,8 @@ 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
@@ -530,8 +532,12 @@ 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);
         }