Xen devel - Jun 2013 - [PATCH, resend] xen-netback: don't de-reference vif pointer after having called xenvif_put()

When putting vif-s on the rx notify list, calling xenvif_put() must be
deferred until after the removal from the list and the issuing of the
notification, as both operations dereference the pointer.

Changing this got me to notice that the "irq" variable was effectively
unused (and was of too narrow type anyway).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

---
 drivers/net/xen-netback/netback.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- 3.10-rc4/drivers/net/xen-netback/netback.c
+++ 3.10-rc4-xen-netback-vif-use-after-free/drivers/net/xen-netback/netback.c
@@ -662,7 +662,7 @@ static void xen_netbk_rx_action(struct x
 {
 	struct xenvif *vif = NULL, *tmp;
 	s8 status;
-	u16 irq, flags;
+	u16 flags;
 	struct xen_netif_rx_response *resp;
 	struct sk_buff_head rxq;
 	struct sk_buff *skb;
@@ -771,13 +771,13 @@ static void xen_netbk_rx_action(struct x
 					 sco->meta_slots_used);
 
 		RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret);
-		irq = vif->irq;
-		if (ret && list_empty(&vif->notify_list))
-			list_add_tail(&vif->notify_list, &notify);
 
 		xenvif_notify_tx_completion(vif);
 
-		xenvif_put(vif);
+		if (ret && list_empty(&vif->notify_list))
+			list_add_tail(&vif->notify_list, &notify);
+		else
+			xenvif_put(vif);
 		npo.meta_cons += sco->meta_slots_used;
 		dev_kfree_skb(skb);
 	}
@@ -785,6 +785,7 @@ static void xen_netbk_rx_action(struct x
 	list_for_each_entry_safe(vif, tmp, &notify, notify_list) {
 		notify_remote_via_irq(vif->irq);
 		list_del_init(&vif->notify_list);
+		xenvif_put(vif);
 	}
 
 	/* More work to do? */

From: "Jan Beulich" <JBeulich@suse.com>
Date: Tue, 11 Jun 2013 11:00:34 +0100
> When putting vif-s on the rx notify list, calling xenvif_put() must be
> deferred until after the removal from the list and the issuing of the
> notification, as both operations dereference the pointer.
> 
> Changing this got me to notice that the "irq" variable was
effectively
> unused (and was of too narrow type anyway).
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
Applied.