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 c879b214a4797383fab79fdb1cc6f61fd33aa4d8..35b1fa6d962ec6f406b2110a2b6d0f80ae34d61c 100644 (file)
--- 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);