HID: hiddev: Fix race in in hiddev_disconnect()

commit 5c02c447eaeda29d3da121a2e17b97ccaf579b51 upstream.

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@syzkaller.appspotmail.com
Fixes: 7f77897ef2b6 ("HID: hiddev: fix potential use-after-free")
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index 8903ea09ac587865748ca2fb2a0c3441f0b9245a..dbdd265075daf264b7fbb8b316174b97daa829b3 100644 (file)
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -962,9 +962,9 @@ void hiddev_disconnect(struct hid_device *hid)
        hiddev->exist = 0;
 
        if (hiddev->open) {
-               mutex_unlock(&hiddev->existancelock);
                usbhid_close(hiddev->hid);
                wake_up_interruptible(&hiddev->wait);
+               mutex_unlock(&hiddev->existancelock);
        } else {
                mutex_unlock(&hiddev->existancelock);
                kfree(hiddev);