[PATCH 1/2] Fix tty refcounting in rfcomm/tty.c

[Gianluca Anzolin <gianluca@xxxxxxxxxxxxxx>]

In net/bluetooth/rfcomm/tty.c the struct tty is used without proper
refcounting. This leads to OOPS and panics triggered by the tty layer functions
which are invoked after the struct tty has already been destroyed.

This happens for example when the bluetooth connection is lost because the host
goes down unexpectedly.

The fix uses the tty_port_* helpers already in place.

This patch depends on patch "Fix refcount leak in tty_port.c" already sent to
linux-kernel. [0]

Signed-off-by: Gianluca Anzolin <gianluca@xxxxxxxxxxxxxx>

[0] http://lkml.indiana.edu/hypermail/linux/kernel/1307.1/00600.html

--- linux/net/bluetooth/rfcomm/tty.c.orig	2013-07-09 18:10:09.071322663 +0200
+++ linux/net/bluetooth/rfcomm/tty.c	2013-07-09 18:14:44.517783673 +0200
@@ -333,10 +333,11 @@ static inline unsigned int rfcomm_room(s
 static void rfcomm_wfree(struct sk_buff *skb)
 {
 	struct rfcomm_dev *dev = (void *) skb->sk;
-	struct tty_struct *tty = dev->port.tty;
+
 	atomic_sub(skb->truesize, &dev->wmem_alloc);
-	if (test_bit(RFCOMM_TTY_ATTACHED, &dev->flags) && tty)
-		tty_wakeup(tty);
+	if (test_bit(RFCOMM_TTY_ATTACHED, &dev->flags))
+		tty_port_tty_wakeup(&dev->port);
+
 	tty_port_put(&dev->port);
 }
 
@@ -410,6 +411,7 @@ static int rfcomm_release_dev(void __use
 {
 	struct rfcomm_dev_req req;
 	struct rfcomm_dev *dev;
+	struct tty_struct *tty;
 
 	if (copy_from_user(&req, arg, sizeof(req)))
 		return -EFAULT;
@@ -429,11 +431,15 @@ static int rfcomm_release_dev(void __use
 		rfcomm_dlc_close(dev->dlc, 0);
 
 	/* Shut down TTY synchronously before freeing rfcomm_dev */
-	if (dev->port.tty)
-		tty_vhangup(dev->port.tty);
+	tty = tty_port_tty_get(&dev->port);
+	if (tty) {
+		tty_vhangup(tty);
+		tty_kref_put(tty);
+	}
 
 	if (!test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags))
 		rfcomm_dev_del(dev);
+
 	tty_port_put(&dev->port);
 	return 0;
 }
@@ -563,6 +569,7 @@ static void rfcomm_dev_data_ready(struct
 static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 {
 	struct rfcomm_dev *dev = dlc->owner;
+	struct tty_struct *tty;
 	if (!dev)
 		return;
 
@@ -572,7 +579,8 @@ static void rfcomm_dev_state_change(stru
 	wake_up_interruptible(&dev->wait);
 
 	if (dlc->state == BT_CLOSED) {
-		if (!dev->port.tty) {
+		tty = tty_port_tty_get(&dev->port);
+		if (!tty) {
 			if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
 				/* Drop DLC lock here to avoid deadlock
 				 * 1. rfcomm_dev_get will take rfcomm_dev_lock
@@ -591,8 +599,10 @@ static void rfcomm_dev_state_change(stru
 				tty_port_put(&dev->port);
 				rfcomm_dlc_lock(dlc);
 			}
-		} else
-			tty_hangup(dev->port.tty);
+		} else {
+			tty_hangup(tty);
+			tty_kref_put(tty);
+		}
 	}
 }
 
@@ -604,10 +614,8 @@ static void rfcomm_dev_modem_status(stru
 
 	BT_DBG("dlc %p dev %p v24_sig 0x%02x", dlc, dev, v24_sig);
 
-	if ((dev->modem_status & TIOCM_CD) && !(v24_sig & RFCOMM_V24_DV)) {
-		if (dev->port.tty && !C_CLOCAL(dev->port.tty))
-			tty_hangup(dev->port.tty);
-	}
+	if ((dev->modem_status & TIOCM_CD) && !(v24_sig & RFCOMM_V24_DV))
+		tty_port_tty_hangup(&dev->port, true);
 
 	dev->modem_status =
 		((v24_sig & RFCOMM_V24_RTC) ? (TIOCM_DSR | TIOCM_DTR) : 0) |
@@ -674,7 +682,7 @@ static int rfcomm_tty_open(struct tty_st
 
 	rfcomm_dlc_lock(dlc);
 	tty->driver_data = dev;
-	dev->port.tty = tty;
+	tty_port_tty_set(&dev->port, tty);
 	rfcomm_dlc_unlock(dlc);
 	set_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
 
@@ -742,7 +750,7 @@ static void rfcomm_tty_close(struct tty_
 
 		rfcomm_dlc_lock(dev->dlc);
 		tty->driver_data = NULL;
-		dev->port.tty = NULL;
+		tty_port_tty_set(&dev->port, NULL);
 		rfcomm_dlc_unlock(dev->dlc);
 
 		if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags)) {