The qca_spi driver stop and restart the SPI kernel thread
(via ndo_stop & ndo_open) in case of TX ring changes. This is
a big issue because it allows userspace to prevent restart of
the SPI kernel thread (via signals). A subsequent change of
TX ring wrongly assume a valid spi_thread pointer which result
in a crash.

So prevent this by stopping the network queue and temporary park
the SPI thread. Because this could happen during transmission
we also need to call qcaspi_flush_tx_ring().

Fixes: 291ab06ecf67 ("net: qualcomm: new Ethernet over SPI driver for QCA7000")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
---
 drivers/net/ethernet/qualcomm/qca_debug.c | 17 ++++++++++++-----
 drivers/net/ethernet/qualcomm/qca_spi.c   |  7 ++++++-
 drivers/net/ethernet/qualcomm/qca_spi.h   |  2 ++
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/qca_debug.c b/drivers/net/ethernet/qualcomm/qca_debug.c
index 6f2fa2a42770..9777dbb17ac2 100644
--- a/drivers/net/ethernet/qualcomm/qca_debug.c
+++ b/drivers/net/ethernet/qualcomm/qca_debug.c
@@ -263,22 +263,29 @@ qcaspi_set_ringparam(struct net_device *dev, struct ethtool_ringparam *ring,
 		     struct kernel_ethtool_ringparam *kernel_ring,
 		     struct netlink_ext_ack *extack)
 {
-	const struct net_device_ops *ops = dev->netdev_ops;
 	struct qcaspi *qca = netdev_priv(dev);
+	bool queue_active = !netif_queue_stopped(dev);

 	if ((ring->rx_pending) ||
 	    (ring->rx_mini_pending) ||
 	    (ring->rx_jumbo_pending))
 		return -EINVAL;

-	if (netif_running(dev))
-		ops->ndo_stop(dev);
+	if (queue_active)
+		netif_stop_queue(dev);

+	if (qca->spi_thread)
+		kthread_park(qca->spi_thread);
+
+	qcaspi_flush_tx_ring(qca);
 	qca->txr.count = max_t(u32, ring->tx_pending, TX_RING_MIN_LEN);
 	qca->txr.count = min_t(u16, qca->txr.count, TX_RING_MAX_LEN);

-	if (netif_running(dev))
-		ops->ndo_open(dev);
+	if (qca->spi_thread)
+		kthread_unpark(qca->spi_thread);
+
+	if (queue_active)
+		netif_wake_queue(dev);

 	return 0;
 }
diff --git a/drivers/net/ethernet/qualcomm/qca_spi.c b/drivers/net/ethernet/qualcomm/qca_spi.c
index bec723028e96..78317b85ad30 100644
--- a/drivers/net/ethernet/qualcomm/qca_spi.c
+++ b/drivers/net/ethernet/qualcomm/qca_spi.c
@@ -467,7 +467,7 @@ qcaspi_tx_ring_has_space(struct tx_ring *txr)
  *   call from the qcaspi_spi_thread.
  */

-static void
+void
 qcaspi_flush_tx_ring(struct qcaspi *qca)
 {
 	int i;
@@ -580,6 +580,11 @@ qcaspi_spi_thread(void *data)
 	netdev_info(qca->net_dev, "SPI thread created\n");
 	while (!kthread_should_stop()) {
 		set_current_state(TASK_INTERRUPTIBLE);
+		if (kthread_should_park()) {
+			kthread_parkme();
+			continue;
+		}
+
 		if ((qca->intr_req == qca->intr_svc) &&
 		    !qca->txr.skb[qca->txr.head])
 			schedule();
diff --git a/drivers/net/ethernet/qualcomm/qca_spi.h b/drivers/net/ethernet/qualcomm/qca_spi.h
index 3067356106f0..95d7306e58e9 100644
--- a/drivers/net/ethernet/qualcomm/qca_spi.h
+++ b/drivers/net/ethernet/qualcomm/qca_spi.h
@@ -107,4 +107,6 @@ struct qcaspi {
 	u16 burst_len;
 };

+void qcaspi_flush_tx_ring(struct qcaspi *qca);
+
 #endif /* _QCA_SPI_H */
--
2.34.1

On Wed, 29 Nov 2023 10:52:39 +0100 Stefan Wahren wrote:
> The qca_spi driver stop and restart the SPI kernel thread
> (via ndo_stop & ndo_open) in case of TX ring changes. This is
> a big issue because it allows userspace to prevent restart of
> the SPI kernel thread (via signals). A subsequent change of
> TX ring wrongly assume a valid spi_thread pointer which result
> in a crash.
> 
> So prevent this by stopping the network queue and temporary park
> the SPI thread. Because this could happen during transmission
> we also need to call qcaspi_flush_tx_ring().
> 
> Fixes: 291ab06ecf67 ("net: qualcomm: new Ethernet over SPI driver for QCA7000")
> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>

Still looks a bit racy.

> diff --git a/drivers/net/ethernet/qualcomm/qca_debug.c b/drivers/net/ethernet/qualcomm/qca_debug.c
> index 6f2fa2a42770..9777dbb17ac2 100644
> --- a/drivers/net/ethernet/qualcomm/qca_debug.c
> +++ b/drivers/net/ethernet/qualcomm/qca_debug.c
> @@ -263,22 +263,29 @@ qcaspi_set_ringparam(struct net_device *dev, struct ethtool_ringparam *ring,
>  		     struct kernel_ethtool_ringparam *kernel_ring,
>  		     struct netlink_ext_ack *extack)
>  {
> -	const struct net_device_ops *ops = dev->netdev_ops;
>  	struct qcaspi *qca = netdev_priv(dev);
> +	bool queue_active = !netif_queue_stopped(dev);

nothing prevents stopped -> running or running -> stopped
transitions at this point, so this check can be meaningful

>  	if ((ring->rx_pending) ||
>  	    (ring->rx_mini_pending) ||
>  	    (ring->rx_jumbo_pending))
>  		return -EINVAL;
> 
> -	if (netif_running(dev))
> -		ops->ndo_stop(dev);
> +	if (queue_active)
> +		netif_stop_queue(dev);

This doesn't wait for xmit to finish, it just sets a bit.
You probably want something like netif_tx_disable().

Also - the thread may still be running and wake the queue up right after
we stop it.
-- 
pw-bot: cr