[char-misc] mei: bus: access mei_device under device_lock on cleanup

[Alexander Usyskin]

Fix couple of problems in mei_cl_bus_dev_release():

mei_cl_flush_queues() is running without lock.
bus->file_list access after mei_dev_bus_put(bus) can become a
use-after-free if this was the last reference to bus.

Protect queues cleanup and WARN traversal by device lock there
to avoid the concurrent access problems.
Move WARN traversal before mei_dev_bus_put(bus).

This file uses bus variable name for mei_device, adjust
code of mei_cl_bus_dev_release() to use bus variable too.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 35e8a426b16a ("mei: bus: Check for still connected devices in mei_cl_bus_dev_release()")
Reviewed-by: Menachem Adin <menachem.adin@xxxxxxxxx>
Signed-off-by: Alexander Usyskin <alexander.usyskin@xxxxxxxxx>
---
 drivers/misc/mei/bus.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/misc/mei/bus.c b/drivers/misc/mei/bus.c
index fcde082eb5e3..cfb87ab8667f 100644
--- a/drivers/misc/mei/bus.c
+++ b/drivers/misc/mei/bus.c
@@ -4,6 +4,7 @@
  * Intel Management Engine Interface (Intel MEI) Linux driver
  */
 
+#include <linux/cleanup.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
@@ -1330,15 +1331,16 @@ static void mei_dev_bus_put(struct mei_device *bus)
 static void mei_cl_bus_dev_release(struct device *dev)
 {
 	struct mei_cl_device *cldev = to_mei_cl_device(dev);
-	struct mei_device *mdev = cldev->cl->dev;
+	struct mei_device *bus = cldev->bus;
 	struct mei_cl *cl;
 
-	mei_cl_flush_queues(cldev->cl, NULL);
-	mei_me_cl_put(cldev->me_cl);
-	mei_dev_bus_put(cldev->bus);
-
-	list_for_each_entry(cl, &mdev->file_list, link)
-		WARN_ON(cl == cldev->cl);
+	scoped_guard(mutex, &bus->device_lock) {
+		mei_cl_flush_queues(cldev->cl, NULL);
+		mei_me_cl_put(cldev->me_cl);
+		list_for_each_entry(cl, &bus->file_list, link)
+			WARN_ON(cl == cldev->cl);
+	}
+	mei_dev_bus_put(bus);
 
 	kfree(cldev->cl);
 	kfree(cldev);
-- 
2.53.0