[PATCH AUTOSEL 5.4 05/58] HID: hiddev: Fix race in in hiddev_disconnect()

[Sasha Levin]

From: "dan.carpenter@xxxxxxxxxx" <dan.carpenter@xxxxxxxxxx>

[ Upstream commit 5c02c447eaeda29d3da121a2e17b97ccaf579b51 ]

Syzbot reports that "hiddev" is used after it's free in hiddev_disconnect().
The hiddev_disconnect() function sets "hiddev->exist = 0;" so
hiddev_release() can free it as soon as we drop the "existancelock"
lock.  This patch moves the mutex_unlock(&hiddev->existancelock) until
after we have finished using it.

Reported-by: syzbot+784ccb935f9900cc7c9e@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 7f77897ef2b6 ("HID: hiddev: fix potential use-after-free")
Suggested-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/hid/usbhid/hiddev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index c879b214a4797..35b1fa6d962ec 100644
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -941,9 +941,9 @@ void hiddev_disconnect(struct hid_device *hid)
 	hiddev->exist = 0;
 
 	if (hiddev->open) {
-		mutex_unlock(&hiddev->existancelock);
 		hid_hw_close(hiddev->hid);
 		wake_up_interruptible(&hiddev->wait);
+		mutex_unlock(&hiddev->existancelock);
 	} else {
 		mutex_unlock(&hiddev->existancelock);
 		kfree(hiddev);
-- 
2.20.1