[PATCH v3 5/5] Input: applespi - fix use-after-free in applespi_remove()

[Shih-Yuan Lee <fourdollars@debian.org>]

Replace the separate read and write drain helpers with a single barrier using
cancel_spi and wait_event_lock_irq_timeout(). Wait for outstanding asynchronous
SPI operations to complete before tearing down the driver context.

Disable GPE and remove the GPE handler prior to setting cancel_spi = true.
This prevents level-triggered GPE interrupt storms where applespi_notify()
repeatedly attempts applespi_async() and gets rejected with -ESHUTDOWN while
the hardware interrupt line remains asserted.

If the 3-second wait times out while SPI transfers are still outstanding, issue
a warning and fallback to waiting unconditionally until all transfers complete,
guaranteeing that applespi_remove() never returns prematurely while transfers
are active.

Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/input/keyboard/applespi.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index a21e89f30387..602780842124 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -1939,14 +1939,29 @@ static void applespi_drain_reads(struct applespi_data *applespi)
 static void applespi_remove(struct spi_device *spi)
 {
 	struct applespi_data *applespi = spi_get_drvdata(spi);
+	unsigned long flags;
+	long ret;
 
-	applespi_drain_writes(applespi);
-
+	/* Disable GPE and remove handler first to prevent interrupt storm */
 	acpi_disable_gpe(NULL, applespi->gpe);
 	acpi_remove_gpe_handler(NULL, applespi->gpe, applespi_notify);
 	device_wakeup_disable(&spi->dev);
 
-	applespi_drain_reads(applespi);
+	/* Prevent any new SPI transfers and wait for outstanding ones */
+	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
+	applespi->cancel_spi = true;
+	ret = wait_event_lock_irq_timeout(applespi->wait_queue,
+					  !applespi_async_outstanding(applespi),
+					  applespi->cmd_msg_lock,
+					  msecs_to_jiffies(3000));
+	if (!ret && applespi_async_outstanding(applespi)) {
+		dev_warn(&applespi->spi->dev,
+			 "Timed out waiting for SPI transfers to drain, waiting unconditionally\n");
+		wait_event_lock_irq(applespi->wait_queue,
+				    !applespi_async_outstanding(applespi),
+				    applespi->cmd_msg_lock);
+	}
+	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
 
 	debugfs_remove_recursive(applespi->debugfs_root);
 }
-- 
2.39.5