[net,v2] xen-netback: avoid race that can lead to NULL pointer dereference
diff mbox series

Message ID 20191213132040.21446-1-pdurrant@amazon.com
State Accepted
Commit fd42bfd1bb31f9a521be6b4f1bd89b85abc08d20
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Series
  • [net,v2] xen-netback: avoid race that can lead to NULL pointer dereference
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Commit Message

Paul Durrant Dec. 13, 2019, 1:20 p.m. UTC
In function xenvif_disconnect_queue(), the value of queue->rx_irq is
zeroed *before* queue->task is stopped. Unfortunately that task may call
notify_remote_via_irq(queue->rx_irq) and calling that function with a
zero value results in a NULL pointer dereference in evtchn_from_irq().

This patch simply re-orders things, stopping all tasks before zero-ing the
irq values, thereby avoiding the possibility of the race.

Fixes: 2ac061ce97f4 ("xen/netback: cleanup init and deinit code")
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Juergen Gross <jgross@suse.com>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>

v2:
 - Add 'Fixes' tag and re-work commit comment
---
 drivers/net/xen-netback/interface.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

Comments

Jakub Kicinski Dec. 15, 2019, 7:41 p.m. UTC | #1
On Fri, 13 Dec 2019 13:20:40 +0000, Paul Durrant wrote:
> In function xenvif_disconnect_queue(), the value of queue->rx_irq is
> zeroed *before* queue->task is stopped. Unfortunately that task may call
> notify_remote_via_irq(queue->rx_irq) and calling that function with a
> zero value results in a NULL pointer dereference in evtchn_from_irq().
> 
> This patch simply re-orders things, stopping all tasks before zero-ing the
> irq values, thereby avoiding the possibility of the race.
> 
> Fixes: 2ac061ce97f4 ("xen/netback: cleanup init and deinit code")
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>

> v2:
>  - Add 'Fixes' tag and re-work commit comment

I've added Wei's Ack from v1, if the code doesn't change substantially
please keep people's Acks.

Applied, thanks.

Patch
diff mbox series

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 68dd7bb07ca6..f15ba3de6195 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -628,18 +628,6 @@  int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
 
 static void xenvif_disconnect_queue(struct xenvif_queue *queue)
 {
-	if (queue->tx_irq) {
-		unbind_from_irqhandler(queue->tx_irq, queue);
-		if (queue->tx_irq == queue->rx_irq)
-			queue->rx_irq = 0;
-		queue->tx_irq = 0;
-	}
-
-	if (queue->rx_irq) {
-		unbind_from_irqhandler(queue->rx_irq, queue);
-		queue->rx_irq = 0;
-	}
-
 	if (queue->task) {
 		kthread_stop(queue->task);
 		queue->task = NULL;
@@ -655,6 +643,18 @@  static void xenvif_disconnect_queue(struct xenvif_queue *queue)
 		queue->napi.poll = NULL;
 	}
 
+	if (queue->tx_irq) {
+		unbind_from_irqhandler(queue->tx_irq, queue);
+		if (queue->tx_irq == queue->rx_irq)
+			queue->rx_irq = 0;
+		queue->tx_irq = 0;
+	}
+
+	if (queue->rx_irq) {
+		unbind_from_irqhandler(queue->rx_irq, queue);
+		queue->rx_irq = 0;
+	}
+
 	xenvif_unmap_frontend_data_rings(queue);
 }