[PATCH v4 0/6] rfcomm: Implement rfcomm as a proper tty_port

[PATCH v4 0/6] rfcomm: Implement rfcomm as a proper tty_port

[Gianluca Anzolin]

This patchset addresses an issue with the rfcomm tty driver in the
current stable kernels that manifests itself as a sudden lockup of the
whole machine or as a OOPS if we are lucky enough (I wasn't).

Triggering the problem is very easy:

1) establish a bluetooth connection with a bluetooth host
2) open the tty it provides with some program
3) turn off the bluetooth host or take it out of range

After a timeout the machine freezes.

Another way to trigger these lockups is to simply release the rfcomm
tty.

This happens because the underlying tty_struct objects and tty_port
objects are freed while being used: the code doesn't take references
properly.

The following patches address the problem by implementing a proper
tty_port driver for rfcomm.

There are still some issues left: one relevant to flow control (which is
also missing in the current code) and another relevant to a corner case
in rfcomm_dev_state_change() that I intend to fix with a future patch.
They are commented with a FIXME.

Thank you,
Gianluca

Gianluca Anzolin (6):
  rfcomm: Take proper tty_struct references
  rfcomm: Remove the device from the list in the destructor
  rfcomm: Move the tty initialization and cleanup out of open/close
  rfcomm: Implement .activate, .shutdown and .carrier_raised methods
  rfcomm: Fix the reference counting of tty_port
  rfcomm: Purge the dlc->tx_queue to avoid circular dependency

 net/bluetooth/rfcomm/tty.c | 263 +++++++++++++++++++++------------------------
 1 file changed, 122 insertions(+), 141 deletions(-)

-- 
1.8.3.4

[PATCH v4 1/6] rfcomm: Take proper tty_struct references

[Gianluca Anzolin]

In net/bluetooth/rfcomm/tty.c the struct tty_struct is used without
taking references. This may lead to a use-after-free of the rfcomm tty.

Fix this by taking references properly, using the tty_port_* helpers
when possible.

The raw assignments of dev->port.tty in rfcomm_tty_open/close are
addressed in the later commit 'rfcomm: Implement .activate, .shutdown
and .carrier_raised methods'.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index b6e44ad..cd7ff37 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -333,10 +333,9 @@ static inline unsigned int rfcomm_room(struct rfcomm_dlc *dlc)
 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 +409,7 @@ static int rfcomm_release_dev(void __user *arg)
 {
 	struct rfcomm_dev_req req;
 	struct rfcomm_dev *dev;
+	struct tty_struct *tty;
 
 	if (copy_from_user(&req, arg, sizeof(req)))
 		return -EFAULT;
@@ -429,8 +429,11 @@ static int rfcomm_release_dev(void __user *arg)
 		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);
@@ -563,6 +566,7 @@ static void rfcomm_dev_data_ready(struct rfcomm_dlc *dlc, struct sk_buff *skb)
 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 +576,8 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 	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 +596,10 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 				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 +611,8 @@ static void rfcomm_dev_modem_status(struct rfcomm_dlc *dlc, u8 v24_sig)
 
 	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) |
-- 
1.8.3.4

[PATCH v4 2/6] rfcomm: Remove the device from the list in the destructor

[Gianluca Anzolin]

The current code removes the device from the device list in several
places. Do it only in the destructor instead and in the error path of
rfcomm_add_dev() if the device couldn't be initialized.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 27 ++++++---------------------
 1 file changed, 6 insertions(+), 21 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index cd7ff37..9c0e142 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -76,13 +76,6 @@ static void rfcomm_dev_modem_status(struct rfcomm_dlc *dlc, u8 v24_sig);
 
 /* ---- Device functions ---- */
 
-/*
- * The reason this isn't actually a race, as you no doubt have a little voice
- * screaming at you in your head, is that the refcount should never actually
- * reach zero unless the device has already been taken off the list, in
- * rfcomm_dev_del(). And if that's not true, we'll hit the BUG() in
- * rfcomm_dev_destruct() anyway.
- */
 static void rfcomm_dev_destruct(struct tty_port *port)
 {
 	struct rfcomm_dev *dev = container_of(port, struct rfcomm_dev, port);
@@ -90,10 +83,9 @@ static void rfcomm_dev_destruct(struct tty_port *port)
 
 	BT_DBG("dev %p dlc %p", dev, dlc);
 
-	/* Refcount should only hit zero when called from rfcomm_dev_del()
-	   which will have taken us off the list. Everything else are
-	   refcounting bugs. */
-	BUG_ON(!list_empty(&dev->list));
+	spin_lock(&rfcomm_dev_lock);
+	list_del(&dev->list);
+	spin_unlock(&rfcomm_dev_lock);
 
 	rfcomm_dlc_lock(dlc);
 	/* Detach DLC if it's owned by this dev */
@@ -282,7 +274,9 @@ out:
 			dev->id, NULL);
 	if (IS_ERR(dev->tty_dev)) {
 		err = PTR_ERR(dev->tty_dev);
+		spin_lock(&rfcomm_dev_lock);
 		list_del(&dev->list);
+		spin_unlock(&rfcomm_dev_lock);
 		goto free;
 	}
 
@@ -315,10 +309,6 @@ static void rfcomm_dev_del(struct rfcomm_dev *dev)
 	}
 	spin_unlock_irqrestore(&dev->port.lock, flags);
 
-	spin_lock(&rfcomm_dev_lock);
-	list_del_init(&dev->list);
-	spin_unlock(&rfcomm_dev_lock);
-
 	tty_port_put(&dev->port);
 }
 
@@ -750,13 +740,8 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
 		dev->port.tty = NULL;
 		rfcomm_dlc_unlock(dev->dlc);
 
-		if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags)) {
-			spin_lock(&rfcomm_dev_lock);
-			list_del_init(&dev->list);
-			spin_unlock(&rfcomm_dev_lock);
-
+		if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
 			tty_port_put(&dev->port);
-		}
 	} else
 		spin_unlock_irqrestore(&dev->port.lock, flags);
 
-- 
1.8.3.4

[PATCH v4 3/6] rfcomm: Move the tty initialization and cleanup out of open/close

[Gianluca Anzolin]

Move the tty_struct initialization from rfcomm_tty_open() to
rfcomm_tty_install() and do the same for the cleanup moving the code from
rfcomm_tty_close() to rfcomm_tty_cleanup().

Add also extra error handling in rfcomm_tty_install() because, unlike
.open()/.close(), .cleanup() is not called if .install() fails.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 108 +++++++++++++++++++++++++++++----------------
 1 file changed, 69 insertions(+), 39 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 9c0e142..bfaa444 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -633,49 +633,64 @@ static void rfcomm_tty_copy_pending(struct rfcomm_dev *dev)
 		tty_flip_buffer_push(&dev->port);
 }
 
-static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
+/* do the reverse of install, clearing the tty fields and releasing the
+ * reference to tty_port
+ */
+static void rfcomm_tty_cleanup(struct tty_struct *tty)
+{
+	struct rfcomm_dev *dev = tty->driver_data;
+
+	if (dev->tty_dev->parent)
+		device_move(dev->tty_dev, NULL, DPM_ORDER_DEV_LAST);
+
+	/* Close DLC and dettach TTY */
+	rfcomm_dlc_close(dev->dlc, 0);
+
+	clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
+
+	rfcomm_dlc_lock(dev->dlc);
+	tty->driver_data = NULL;
+	dev->port.tty = NULL;
+	rfcomm_dlc_unlock(dev->dlc);
+
+	tty_port_put(&dev->port);
+}
+
+/* we acquire the tty_port reference since it's here the tty is first used
+ * by setting the termios. We also populate the driver_data field and install
+ * the tty port
+ */
+static int rfcomm_tty_install(struct tty_driver *driver, struct tty_struct *tty)
 {
 	DECLARE_WAITQUEUE(wait, current);
 	struct rfcomm_dev *dev;
 	struct rfcomm_dlc *dlc;
-	unsigned long flags;
-	int err, id;
-
-	id = tty->index;
+	int err;
 
-	BT_DBG("tty %p id %d", tty, id);
-
-	/* We don't leak this refcount. For reasons which are not entirely
-	   clear, the TTY layer will call our ->close() method even if the
-	   open fails. We decrease the refcount there, and decreasing it
-	   here too would cause breakage. */
-	dev = rfcomm_dev_get(id);
+	dev = rfcomm_dev_get(tty->index);
 	if (!dev)
 		return -ENODEV;
 
 	BT_DBG("dev %p dst %pMR channel %d opened %d", dev, &dev->dst,
 	       dev->channel, dev->port.count);
 
-	spin_lock_irqsave(&dev->port.lock, flags);
-	if (++dev->port.count > 1) {
-		spin_unlock_irqrestore(&dev->port.lock, flags);
-		return 0;
-	}
-	spin_unlock_irqrestore(&dev->port.lock, flags);
-
 	dlc = dev->dlc;
 
 	/* Attach TTY and open DLC */
-
 	rfcomm_dlc_lock(dlc);
 	tty->driver_data = dev;
 	dev->port.tty = tty;
 	rfcomm_dlc_unlock(dlc);
 	set_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
 
+	/* install the tty_port */
+	err = tty_port_install(&dev->port, driver, tty);
+	if (err < 0)
+		goto error_no_dlc;
+
 	err = rfcomm_dlc_open(dlc, &dev->src, &dev->dst, dev->channel);
 	if (err < 0)
-		return err;
+		goto error_no_dlc;
 
 	/* Wait for DLC to connect */
 	add_wait_queue(&dev->wait, &wait);
@@ -702,15 +717,42 @@ static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&dev->wait, &wait);
 
-	if (err == 0)
-		device_move(dev->tty_dev, rfcomm_get_device(dev),
-			    DPM_ORDER_DEV_AFTER_PARENT);
+	if (err < 0)
+		goto error_no_connection;
+
+	device_move(dev->tty_dev, rfcomm_get_device(dev),
+		    DPM_ORDER_DEV_AFTER_PARENT);
+	return 0;
+
+error_no_connection:
+	rfcomm_dlc_close(dlc, err);
+error_no_dlc:
+	clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
+	tty_port_put(&dev->port);
+	return err;
+}
+
+static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
+{
+	struct rfcomm_dev *dev = tty->driver_data;
+	unsigned long flags;
+
+	BT_DBG("tty %p id %d", tty, tty->index);
+
+	spin_lock_irqsave(&dev->port.lock, flags);
+	dev->port.count++;
+	spin_unlock_irqrestore(&dev->port.lock, flags);
 
+	/*
+	 * FIXME: rfcomm should use proper flow control for
+	 * received data. This hack will be unnecessary and can
+	 * be removed when that's implemented
+	 */
 	rfcomm_tty_copy_pending(dev);
 
 	rfcomm_dlc_unthrottle(dev->dlc);
 
-	return err;
+	return 0;
 }
 
 static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
@@ -727,25 +769,11 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
 	spin_lock_irqsave(&dev->port.lock, flags);
 	if (!--dev->port.count) {
 		spin_unlock_irqrestore(&dev->port.lock, flags);
-		if (dev->tty_dev->parent)
-			device_move(dev->tty_dev, NULL, DPM_ORDER_DEV_LAST);
-
-		/* Close DLC and dettach TTY */
-		rfcomm_dlc_close(dev->dlc, 0);
-
-		clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
-
-		rfcomm_dlc_lock(dev->dlc);
-		tty->driver_data = NULL;
-		dev->port.tty = NULL;
-		rfcomm_dlc_unlock(dev->dlc);
 
 		if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
 			tty_port_put(&dev->port);
 	} else
 		spin_unlock_irqrestore(&dev->port.lock, flags);
-
-	tty_port_put(&dev->port);
 }
 
 static int rfcomm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
@@ -1118,6 +1146,8 @@ static const struct tty_operations rfcomm_ops = {
 	.wait_until_sent	= rfcomm_tty_wait_until_sent,
 	.tiocmget		= rfcomm_tty_tiocmget,
 	.tiocmset		= rfcomm_tty_tiocmset,
+	.install                = rfcomm_tty_install,
+	.cleanup                = rfcomm_tty_cleanup,
 };
 
 int __init rfcomm_init_ttys(void)
-- 
1.8.3.4

[PATCH v4 4/6] rfcomm: Implement .activate, .shutdown and .carrier_raised methods

[Gianluca Anzolin]

Implement .activate, .shutdown and .carrier_raised methods of tty_port
to manage the dlc, moving the code from rfcomm_tty_install() and
rfcomm_tty_cleanup() functions.

At the same time the tty .open()/.close() and .hangup() methods are
changed to use the tty_port helpers that properly call the
aforementioned tty_port methods.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 117 ++++++++++++++++++---------------------------
 1 file changed, 47 insertions(+), 70 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index bfaa444..24a7c8c 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -58,7 +58,6 @@ struct rfcomm_dev {
 	uint			modem_status;
 
 	struct rfcomm_dlc	*dlc;
-	wait_queue_head_t       wait;
 
 	struct device		*tty_dev;
 
@@ -104,8 +103,39 @@ static void rfcomm_dev_destruct(struct tty_port *port)
 	module_put(THIS_MODULE);
 }
 
+/* device-specific initialization: open the dlc */
+static int rfcomm_dev_activate(struct tty_port *port, struct tty_struct *tty)
+{
+	struct rfcomm_dev *dev = container_of(port, struct rfcomm_dev, port);
+
+	return rfcomm_dlc_open(dev->dlc, &dev->src, &dev->dst, dev->channel);
+}
+
+/* we block the open until the dlc->state becomes BT_CONNECTED */
+static int rfcomm_dev_carrier_raised(struct tty_port *port)
+{
+	struct rfcomm_dev *dev = container_of(port, struct rfcomm_dev, port);
+
+	return (dev->dlc->state == BT_CONNECTED);
+}
+
+/* device-specific cleanup: close the dlc */
+static void rfcomm_dev_shutdown(struct tty_port *port)
+{
+	struct rfcomm_dev *dev = container_of(port, struct rfcomm_dev, port);
+
+	if (dev->tty_dev->parent)
+		device_move(dev->tty_dev, NULL, DPM_ORDER_DEV_LAST);
+
+	/* close the dlc */
+	rfcomm_dlc_close(dev->dlc, 0);
+}
+
 static const struct tty_port_operations rfcomm_port_ops = {
 	.destruct = rfcomm_dev_destruct,
+	.activate = rfcomm_dev_activate,
+	.shutdown = rfcomm_dev_shutdown,
+	.carrier_raised = rfcomm_dev_carrier_raised,
 };
 
 static struct rfcomm_dev *__rfcomm_dev_get(int id)
@@ -228,7 +258,6 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
 
 	tty_port_init(&dev->port);
 	dev->port.ops = &rfcomm_port_ops;
-	init_waitqueue_head(&dev->wait);
 
 	skb_queue_head_init(&dev->pending);
 
@@ -563,9 +592,12 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 	BT_DBG("dlc %p dev %p err %d", dlc, dev, err);
 
 	dev->err = err;
-	wake_up_interruptible(&dev->wait);
+	if (dlc->state == BT_CONNECTED) {
+		device_move(dev->tty_dev, rfcomm_get_device(dev),
+			    DPM_ORDER_DEV_AFTER_PARENT);
 
-	if (dlc->state == BT_CLOSED) {
+		wake_up_interruptible(&dev->port.open_wait);
+	} else if (dlc->state == BT_CLOSED) {
 		tty = tty_port_tty_get(&dev->port);
 		if (!tty) {
 			if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
@@ -640,17 +672,10 @@ static void rfcomm_tty_cleanup(struct tty_struct *tty)
 {
 	struct rfcomm_dev *dev = tty->driver_data;
 
-	if (dev->tty_dev->parent)
-		device_move(dev->tty_dev, NULL, DPM_ORDER_DEV_LAST);
-
-	/* Close DLC and dettach TTY */
-	rfcomm_dlc_close(dev->dlc, 0);
-
 	clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
 
 	rfcomm_dlc_lock(dev->dlc);
 	tty->driver_data = NULL;
-	dev->port.tty = NULL;
 	rfcomm_dlc_unlock(dev->dlc);
 
 	tty_port_put(&dev->port);
@@ -662,7 +687,6 @@ static void rfcomm_tty_cleanup(struct tty_struct *tty)
  */
 static int rfcomm_tty_install(struct tty_driver *driver, struct tty_struct *tty)
 {
-	DECLARE_WAITQUEUE(wait, current);
 	struct rfcomm_dev *dev;
 	struct rfcomm_dlc *dlc;
 	int err;
@@ -679,69 +703,27 @@ static int rfcomm_tty_install(struct tty_driver *driver, struct tty_struct *tty)
 	/* Attach TTY and open DLC */
 	rfcomm_dlc_lock(dlc);
 	tty->driver_data = dev;
-	dev->port.tty = tty;
 	rfcomm_dlc_unlock(dlc);
 	set_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
 
 	/* install the tty_port */
 	err = tty_port_install(&dev->port, driver, tty);
-	if (err < 0)
-		goto error_no_dlc;
-
-	err = rfcomm_dlc_open(dlc, &dev->src, &dev->dst, dev->channel);
-	if (err < 0)
-		goto error_no_dlc;
+	if (err)
+		rfcomm_tty_cleanup(tty);
 
-	/* Wait for DLC to connect */
-	add_wait_queue(&dev->wait, &wait);
-	while (1) {
-		set_current_state(TASK_INTERRUPTIBLE);
-
-		if (dlc->state == BT_CLOSED) {
-			err = -dev->err;
-			break;
-		}
-
-		if (dlc->state == BT_CONNECTED)
-			break;
-
-		if (signal_pending(current)) {
-			err = -EINTR;
-			break;
-		}
-
-		tty_unlock(tty);
-		schedule();
-		tty_lock(tty);
-	}
-	set_current_state(TASK_RUNNING);
-	remove_wait_queue(&dev->wait, &wait);
-
-	if (err < 0)
-		goto error_no_connection;
-
-	device_move(dev->tty_dev, rfcomm_get_device(dev),
-		    DPM_ORDER_DEV_AFTER_PARENT);
-	return 0;
-
-error_no_connection:
-	rfcomm_dlc_close(dlc, err);
-error_no_dlc:
-	clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
-	tty_port_put(&dev->port);
 	return err;
 }
 
 static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
 {
 	struct rfcomm_dev *dev = tty->driver_data;
-	unsigned long flags;
+	int err;
 
 	BT_DBG("tty %p id %d", tty, tty->index);
 
-	spin_lock_irqsave(&dev->port.lock, flags);
-	dev->port.count++;
-	spin_unlock_irqrestore(&dev->port.lock, flags);
+	err = tty_port_open(&dev->port, tty, filp);
+	if (err)
+		return err;
 
 	/*
 	 * FIXME: rfcomm should use proper flow control for
@@ -758,7 +740,6 @@ static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
 static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
 {
 	struct rfcomm_dev *dev = (struct rfcomm_dev *) tty->driver_data;
-	unsigned long flags;
 
 	if (!dev)
 		return;
@@ -766,14 +747,10 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
 	BT_DBG("tty %p dev %p dlc %p opened %d", tty, dev, dev->dlc,
 						dev->port.count);
 
-	spin_lock_irqsave(&dev->port.lock, flags);
-	if (!--dev->port.count) {
-		spin_unlock_irqrestore(&dev->port.lock, flags);
+	tty_port_close(&dev->port, tty, filp);
 
-		if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
-			tty_port_put(&dev->port);
-	} else
-		spin_unlock_irqrestore(&dev->port.lock, flags);
+	if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
+		tty_port_put(&dev->port);
 }
 
 static int rfcomm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
@@ -1076,7 +1053,7 @@ static void rfcomm_tty_hangup(struct tty_struct *tty)
 	if (!dev)
 		return;
 
-	rfcomm_tty_flush_buffer(tty);
+	tty_port_hangup(&dev->port);
 
 	if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
 		if (rfcomm_dev_get(dev->id) == NULL)
@@ -1166,7 +1143,7 @@ int __init rfcomm_init_ttys(void)
 	rfcomm_tty_driver->subtype	= SERIAL_TYPE_NORMAL;
 	rfcomm_tty_driver->flags	= TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
 	rfcomm_tty_driver->init_termios	= tty_std_termios;
-	rfcomm_tty_driver->init_termios.c_cflag	= B9600 | CS8 | CREAD | HUPCL | CLOCAL;
+	rfcomm_tty_driver->init_termios.c_cflag	= B9600 | CS8 | CREAD | HUPCL;
 	rfcomm_tty_driver->init_termios.c_lflag &= ~ICANON;
 	tty_set_operations(rfcomm_tty_driver, &rfcomm_ops);
 
-- 
1.8.3.4

[PATCH v4 5/6] rfcomm: Fix the reference counting of tty_port

[Gianluca Anzolin]

The tty_port can be released in two cases: when we get a HUP in the
functions rfcomm_tty_hangup() and rfcomm_dev_state_change(). Or when the
user releases the device in rfcomm_release_dev().

In these cases we set the flag RFCOMM_TTY_RELEASED so that no other
function can get a reference to the tty_port.

The rfcomm_dev_del function is removed becase it isn't used anymore.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 42 ++++++++++--------------------------------
 1 file changed, 10 insertions(+), 32 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 24a7c8c..9def67a 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -324,23 +324,6 @@ free:
 	return err;
 }
 
-static void rfcomm_dev_del(struct rfcomm_dev *dev)
-{
-	unsigned long flags;
-	BT_DBG("dev %p", dev);
-
-	BUG_ON(test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags));
-
-	spin_lock_irqsave(&dev->port.lock, flags);
-	if (dev->port.count > 0) {
-		spin_unlock_irqrestore(&dev->port.lock, flags);
-		return;
-	}
-	spin_unlock_irqrestore(&dev->port.lock, flags);
-
-	tty_port_put(&dev->port);
-}
-
 /* ---- Send buffer ---- */
 static inline unsigned int rfcomm_room(struct rfcomm_dlc *dlc)
 {
@@ -454,8 +437,9 @@ static int rfcomm_release_dev(void __user *arg)
 		tty_kref_put(tty);
 	}
 
-	if (!test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags))
-		rfcomm_dev_del(dev);
+	if (!test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags))
+		tty_port_put(&dev->port);
+
 	tty_port_put(&dev->port);
 	return 0;
 }
@@ -607,6 +591,9 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 				 *    rfcomm_dev_lock -> dlc lock
 				 * 2. tty_port_put will deadlock if it's
 				 *    the last reference
+				 *
+				 * FIXME: when we release the lock anything
+				 * could happen to dev, even its destruction
 				 */
 				rfcomm_dlc_unlock(dlc);
 				if (rfcomm_dev_get(dev->id) == NULL) {
@@ -614,7 +601,9 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
 					return;
 				}
 
-				rfcomm_dev_del(dev);
+				set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
+				tty_port_put(&dev->port);
+
 				tty_port_put(&dev->port);
 				rfcomm_dlc_lock(dlc);
 			}
@@ -741,16 +730,10 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
 {
 	struct rfcomm_dev *dev = (struct rfcomm_dev *) tty->driver_data;
 
-	if (!dev)
-		return;
-
 	BT_DBG("tty %p dev %p dlc %p opened %d", tty, dev, dev->dlc,
 						dev->port.count);
 
 	tty_port_close(&dev->port, tty, filp);
-
-	if (test_bit(RFCOMM_TTY_RELEASED, &dev->flags))
-		tty_port_put(&dev->port);
 }
 
 static int rfcomm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
@@ -1050,15 +1033,10 @@ static void rfcomm_tty_hangup(struct tty_struct *tty)
 
 	BT_DBG("tty %p dev %p", tty, dev);
 
-	if (!dev)
-		return;
-
 	tty_port_hangup(&dev->port);
 
 	if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
-		if (rfcomm_dev_get(dev->id) == NULL)
-			return;
-		rfcomm_dev_del(dev);
+		set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
 		tty_port_put(&dev->port);
 	}
 }
-- 
1.8.3.4

[PATCH v4 6/6] rfcomm: Purge the dlc->tx_queue to avoid circular dependency

[Gianluca Anzolin]

In rfcomm_tty_cleanup we purge the dlc->tx_queue which may contain
socket buffers referencing the tty_port and thus preventing the tty_port
destruction.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---
 net/bluetooth/rfcomm/tty.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 9def67a..1c6bd90 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -667,6 +667,12 @@ static void rfcomm_tty_cleanup(struct tty_struct *tty)
 	tty->driver_data = NULL;
 	rfcomm_dlc_unlock(dev->dlc);
 
+	/*
+	 * purge the dlc->tx_queue to avoid circular dependencies
+	 * between dev and dlc
+	 */
+	skb_queue_purge(&dev->dlc->tx_queue);
+
 	tty_port_put(&dev->port);
 }
 
-- 
1.8.3.4

Re: [PATCH v4 0/6] rfcomm: Implement rfcomm as a proper tty_port

[Peter Hurley]

On 07/26/2013 01:18 PM, Gianluca Anzolin wrote:
> This patchset addresses an issue with the rfcomm tty driver in the
> current stable kernels that manifests itself as a sudden lockup of the
> whole machine or as a OOPS if we are lucky enough (I wasn't).
>
> Triggering the problem is very easy:
>
> 1) establish a bluetooth connection with a bluetooth host
> 2) open the tty it provides with some program
> 3) turn off the bluetooth host or take it out of range
>
> After a timeout the machine freezes.
>
> Another way to trigger these lockups is to simply release the rfcomm
> tty.
>
> This happens because the underlying tty_struct objects and tty_port
> objects are freed while being used: the code doesn't take references
> properly.
>
> The following patches address the problem by implementing a proper
> tty_port driver for rfcomm.
>
> There are still some issues left: one relevant to flow control (which is
> also missing in the current code) and another relevant to a corner case
> in rfcomm_dev_state_change() that I intend to fix with a future patch.
> They are commented with a FIXME.
>
> Thank you,
> Gianluca

Gianluca,

Looks good, nice job :)  [ Thanks for the cover letter. ]

I tested device disconnect with i/o both in-progress and while idle.
I also tested remote disconnect and local device release.
Teardown was clean and complete with all tests.

[ Sorry that it took me a little while. I first had to review the
tools/rfcomm.c code to figure out the parameters expected! since
there were no examples on the man page. Then I had to disable the
pnat plugin because the error path when it's not installed closes
the wrong file! ]

I have a minor comment on 4/6 regarding one of the debug printks.
Other than that;

Reviewed-and-Tested-by: Peter Hurley <peter@hurleysoftware.com>

If Gustavo has you change stuff, please note changes in the cover
letter and in the patch itself below your sign-off line [example below],
so that I can follow along without re-reviewing the entire patch.

Regards,
Peter Hurley

--- >% ----
Implement .activate, .shutdown and .carrier_raised methods of tty_port
to manage the dlc, moving the code from rfcomm_tty_install() and
rfcomm_tty_cleanup() functions.

At the same time the tty .open()/.close() and .hangup() methods are
changed to use the tty_port helpers that properly call the
aforementioned tty_port methods.

Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
---

  v5 - Fixed debug message in rfcomm_tty_activate()

  net/bluetooth/rfcomm/tty.c | 117 ++++++++++++++++++---------------------------
  1 file changed, 47 insertions(+), 70 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
.....

Re: [PATCH v4 3/6] rfcomm: Move the tty initialization and cleanup out of open/close

[Peter Hurley]

On 07/26/2013 01:18 PM, Gianluca Anzolin wrote:
> Move the tty_struct initialization from rfcomm_tty_open() to
> rfcomm_tty_install() and do the same for the cleanup moving the code from
> rfcomm_tty_close() to rfcomm_tty_cleanup().
>
> Add also extra error handling in rfcomm_tty_install() because, unlike
> .open()/.close(), .cleanup() is not called if .install() fails.
>
> Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
> ---
>   net/bluetooth/rfcomm/tty.c | 108 +++++++++++++++++++++++++++++----------------
>   1 file changed, 69 insertions(+), 39 deletions(-)
>
> diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
> index 9c0e142..bfaa444 100644
> --- a/net/bluetooth/rfcomm/tty.c
> +++ b/net/bluetooth/rfcomm/tty.c
> @@ -633,49 +633,64 @@ static void rfcomm_tty_copy_pending(struct rfcomm_dev *dev)
>   		tty_flip_buffer_push(&dev->port);
>   }
>
> -static int rfcomm_tty_open(struct tty_struct *tty, struct file *filp)
> +/* do the reverse of install, clearing the tty fields and releasing the
> + * reference to tty_port
> + */
> +static void rfcomm_tty_cleanup(struct tty_struct *tty)
> +{
> +	struct rfcomm_dev *dev = tty->driver_data;
> +
> +	if (dev->tty_dev->parent)
> +		device_move(dev->tty_dev, NULL, DPM_ORDER_DEV_LAST);
> +
> +	/* Close DLC and dettach TTY */
> +	rfcomm_dlc_close(dev->dlc, 0);
> +
> +	clear_bit(RFCOMM_TTY_ATTACHED, &dev->flags);
> +
> +	rfcomm_dlc_lock(dev->dlc);
> +	tty->driver_data = NULL;
> +	dev->port.tty = NULL;
> +	rfcomm_dlc_unlock(dev->dlc);
> +
> +	tty_port_put(&dev->port);
> +}
> +
> +/* we acquire the tty_port reference since it's here the tty is first used
> + * by setting the termios. We also populate the driver_data field and install
> + * the tty port
> + */
> +static int rfcomm_tty_install(struct tty_driver *driver, struct tty_struct *tty)
>   {
>   	DECLARE_WAITQUEUE(wait, current);
>   	struct rfcomm_dev *dev;
>   	struct rfcomm_dlc *dlc;
> -	unsigned long flags;
> -	int err, id;
> -
> -	id = tty->index;
> +	int err;
>
> -	BT_DBG("tty %p id %d", tty, id);
> -
> -	/* We don't leak this refcount. For reasons which are not entirely
> -	   clear, the TTY layer will call our ->close() method even if the
> -	   open fails. We decrease the refcount there, and decreasing it
> -	   here too would cause breakage. */
> -	dev = rfcomm_dev_get(id);
> +	dev = rfcomm_dev_get(tty->index);
>   	if (!dev)
>   		return -ENODEV;
>


>   	BT_DBG("dev %p dst %pMR channel %d opened %d", dev, &dev->dst,
>   	       dev->channel, dev->port.count);

This debug message is probably more useful in rfcomm_tty_open().
But if you decide to leave it here, the port count will always be 0 so
that field should be removed.

Regards,
Peter Hurley

Re: [PATCH v4 5/6] rfcomm: Fix the reference counting of tty_port

[Peter Hurley]

On 07/26/2013 01:18 PM, Gianluca Anzolin wrote:
> The tty_port can be released in two cases: when we get a HUP in the
> functions rfcomm_tty_hangup() and rfcomm_dev_state_change(). Or when the
> user releases the device in rfcomm_release_dev().
>
> In these cases we set the flag RFCOMM_TTY_RELEASED so that no other
> function can get a reference to the tty_port.
>
> The rfcomm_dev_del function is removed becase it isn't used anymore.

While reviewing your RFC patch for fixing rfcomm_dev_state_change(),
I realized I missed a problem in this patch.

> @@ -614,7 +601,9 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
>   					return;
>   				}
>
> -				rfcomm_dev_del(dev);
> +				set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
> +				tty_port_put(&dev->port);

Since this code can execute concurrently with rfcomm_release_dev(),
and the 'initial' port reference must only be dropped once, this should be

				if (!test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags)
					tty_port_put(&dev->port);

Regards,
Peter Hurley

Re: [PATCH v4 5/6] rfcomm: Fix the reference counting of tty_port

[Gianluca Anzolin]

On Fri, Jul 26, 2013 at 08:20:47PM -0400, Peter Hurley wrote:
> On 07/26/2013 01:18 PM, Gianluca Anzolin wrote:
> >@@ -614,7 +601,9 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
> >  					return;
> >  				}
> >
> >-				rfcomm_dev_del(dev);
> >+				set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
> >+				tty_port_put(&dev->port);
> 
> Since this code can execute concurrently with rfcomm_release_dev(),
> and the 'initial' port reference must only be dropped once, this should be
> 
> 				if (!test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags)
> 					tty_port_put(&dev->port);
> 
> Regards,
> Peter Hurley

I somehow convinced myself that it was safe but clearly it wasn't. Should I
also change the same way the code in rfcomm_tty_hangup()?

Thanks,

Gianluca

Re: [PATCH v4 5/6] rfcomm: Fix the reference counting of tty_port

[Peter Hurley]

On 07/27/2013 12:48 AM, Gianluca Anzolin wrote:
> On Fri, Jul 26, 2013 at 08:20:47PM -0400, Peter Hurley wrote:
>> On 07/26/2013 01:18 PM, Gianluca Anzolin wrote:
>>> @@ -614,7 +601,9 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
>>>   					return;
>>>   				}
>>>
>>> -				rfcomm_dev_del(dev);
>>> +				set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
>>> +				tty_port_put(&dev->port);
>>
>> Since this code can execute concurrently with rfcomm_release_dev(),
>> and the 'initial' port reference must only be dropped once, this should be
>>
>> 				if (!test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags)
>> 					tty_port_put(&dev->port);
>>
>> Regards,
>> Peter Hurley
>
> I somehow convinced myself that it was safe but clearly it wasn't. Should I
> also change the same way the code in rfcomm_tty_hangup()?

Yes, I think that's wise. For example,

CPU 0                                  | CPU 1
                                        |
rfcomm_dev_state_change                |
   tty_port_tty_get                     |
     tty_hangup                         | rfcomm_release_dev
      .                                 |   .
      .                                 |   .
      .                                 |   .
     do_tty_hangup                      |   .
       __tty_hangup                     |   .
         rfcomm_tty_hangup              |   .
           tty_port_hangup              |   .
                                        |   if (!test_and_set_bit(RFCOMM_TTY_RELEASED))
                                        |     tty_port_put
           set_bit(RFCOMM_TTY_RELEASED) |
           tty_port_put                 |

Also, in the commit message you should explain that
!test_and_set_bit(RFCOMM_TTY_RELEASED) ensures that the 'initial'
tty_port reference is only dropped once.

On a side note, I think this exposes a flaw in the tty layer hangup handling.
It seems possible that an async hangup could be scheduled while a
sync hangup is in-progress (and vice versa). While the two hangups would
not execute concurrently (because the tty lock serializes hangups),
they would execute sequentially and that would be bad.

I'm testing a mock-up now.

Regards,
Peter Hurley