[PATCH net v4 2/2] net: ravb: serialize PTP clock teardown

From: Xuanqiang Luo <[email protected]>

ravb_ptp_interrupt() can race with ravb_ptp_stop() and pass the clock to
ptp_clock_event() while ptp_clock_unregister() is freeing it. This can
lead to a use-after-free.

Use READ_ONCE() and WRITE_ONCE() for lockless access to the clock pointer.
Atomically detach it with xchg() before disabling PTP interrupts, then
synchronize all IRQs which can invoke ravb_ptp_interrupt() before
unregistering the detached clock.

A handler which read the old pointer completes before the clock is
unregistered, while later handlers read NULL and skip the event.

Fixes: a0d2f20650e8 ("Renesas Ethernet AVB PTP clock driver")
Cc: [email protected]
Signed-off-by: Xuanqiang Luo <[email protected]>
---
 drivers/net/ethernet/renesas/ravb.h      |  2 ++
 drivers/net/ethernet/renesas/ravb_main.c |  6 ++--
 drivers/net/ethernet/renesas/ravb_ptp.c  | 37 +++++++++++++++++++-----
 3 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
index 2a4fcb12a63cb..3ee4c61081890 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -1124,6 +1124,8 @@ struct ravb_private {
 	int msg_enable;
 	int speed;
 	int emac_irq;
+	int err_irq;
+	int mgmt_irq;
 
 	unsigned no_avb_link:1;
 	unsigned avb_link_active_low:1;
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index db0229e008494..ea1c7e536791e 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2885,11 +2885,13 @@ static int ravb_setup_irqs(struct ravb_private *priv)
 		return error;
 
 	if (info->err_mgmt_irqs) {
-		error = ravb_setup_irq(priv, "err_a", "err_a", NULL, ravb_multi_interrupt);
+		error = ravb_setup_irq(priv, "err_a", "err_a", &priv->err_irq,
+				       ravb_multi_interrupt);
 		if (error)
 			return error;
 
-		error = ravb_setup_irq(priv, "mgmt_a", "mgmt_a", NULL, ravb_multi_interrupt);
+		error = ravb_setup_irq(priv, "mgmt_a", "mgmt_a", &priv->mgmt_irq,
+				       ravb_multi_interrupt);
 		if (error)
 			return error;
 	}
diff --git a/drivers/net/ethernet/renesas/ravb_ptp.c b/drivers/net/ethernet/renesas/ravb_ptp.c
index cbec7c057d715..43218bc15b151 100644
--- a/drivers/net/ethernet/renesas/ravb_ptp.c
+++ b/drivers/net/ethernet/renesas/ravb_ptp.c
@@ -289,16 +289,17 @@ static const struct ptp_clock_info ravb_ptp_info = {
 void ravb_ptp_interrupt(struct net_device *ndev)
 {
 	struct ravb_private *priv = netdev_priv(ndev);
+	struct ptp_clock *clock = READ_ONCE(priv->ptp.clock);
 	u32 gis = ravb_read(ndev, GIS);
 
 	gis &= ravb_read(ndev, GIC);
-	if (gis & GIS_PTCF) {
+	if ((gis & GIS_PTCF) && clock) {
 		struct ptp_clock_event event;
 
 		event.type = PTP_CLOCK_EXTTS;
 		event.index = 0;
 		event.timestamp = ravb_read(ndev, GCPT);
-		ptp_clock_event(priv->ptp.clock, &event);
+		ptp_clock_event(clock, &event);
 	}
 	if (gis & GIS_PTMF) {
 		struct ravb_ptp_perout *perout = priv->ptp.perout;
@@ -334,19 +335,39 @@ void ravb_ptp_init(struct net_device *ndev, struct platform_device *pdev)
 		clock = NULL;
 	}
 
-	priv->ptp.clock = clock;
+	WRITE_ONCE(priv->ptp.clock, clock);
 	if (clock)
 		WRITE_ONCE(priv->ptp.phc_index, ptp_clock_index(clock));
 }
 
-void ravb_ptp_stop(struct net_device *ndev)
+static void ravb_ptp_disable(struct net_device *ndev)
 {
-	struct ravb_private *priv = netdev_priv(ndev);
-
 	ravb_write(ndev, 0, GIC);
 	ravb_write(ndev, 0, GIS);
+}
+
+static void ravb_ptp_sync_irqs(struct net_device *ndev)
+{
+	struct ravb_private *priv = netdev_priv(ndev);
+
+	synchronize_irq(ndev->irq);
+	if (priv->info->err_mgmt_irqs) {
+		synchronize_irq(priv->err_irq);
+		synchronize_irq(priv->mgmt_irq);
+	}
+}
+
+void ravb_ptp_stop(struct net_device *ndev)
+{
+	struct ravb_private *priv = netdev_priv(ndev);
+	struct ptp_clock *clock;
 
 	WRITE_ONCE(priv->ptp.phc_index, -1);
-	if (priv->ptp.clock)
-		ptp_clock_unregister(priv->ptp.clock);
+	clock = xchg(&priv->ptp.clock, NULL);
+
+	ravb_ptp_disable(ndev);
+	ravb_ptp_sync_irqs(ndev);
+
+	if (clock)
+		ptp_clock_unregister(clock);
 }
-- 
2.43.0