[Xen-devel] [PATCH net 3/3] xen-netback: BUG_ON in xenvif_rx_action() not catching overflow

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

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@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
---
 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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