| Message ID | 20191212123723.21548-1-pdurrant@amazon.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [net] xen-netback: avoid race that can lead to NULL pointer dereference | expand |
On Thu, Dec 12, 2019 at 12:37:23PM +0000, Paul Durrant wrote: > Commit 2ac061ce97f4 ("xen/netback: cleanup init and deinit code") > introduced a problem. 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. > > Signed-off-by: Paul Durrant <pdurrant@amazon.com> Acked-by: Wei Liu <wei.liu@kernel.org>
From: Paul Durrant <pdurrant@amazon.com> Date: Thu, 12 Dec 2019 12:37:23 +0000 > Commit 2ac061ce97f4 ("xen/netback: cleanup init and deinit code") > introduced a problem. 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. > > Signed-off-by: Paul Durrant <pdurrant@amazon.com> Please repost this with an appropriate Fixes: tag. And then you can removed the explicit commit reference from the log message and simply say "The commit mentioned in the Fixes tag introduced a problen ..."
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); }
Commit 2ac061ce97f4 ("xen/netback: cleanup init and deinit code") introduced a problem. 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. 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> --- drivers/net/xen-netback/interface.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-)