Bluetooth: RFCOMM: fix ODEBUG bug in rfcomm_dev_ioctl

BugLink: https://bugs.launchpad.net/bugs/1874045

commit 71811cac upstream.

Needn't call 'rfcomm_dlc_put' here, because 'rfcomm_dlc_exists' didn't
increase dlc->refcnt.

Reported-by: syzbot+4496e82090657320efc6@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/bluetooth/rfcomm/tty.c

@@ -413,10 +413,8 @@ static int __rfcomm_create_dev(struct sock *sk, void __user *arg)
 		dlc = rfcomm_dlc_exists(&req.src, &req.dst, req.channel);
 		if (IS_ERR(dlc))
 			return PTR_ERR(dlc);
-		else if (dlc) {
-			rfcomm_dlc_put(dlc);
+		if (dlc)
 			return -EBUSY;
-		}
 		dlc = rfcomm_dlc_alloc(GFP_KERNEL);
 		if (!dlc)
 			return -ENOMEM;