linux-kernel - [PATCH 09/24] Bluetooth: Fix RFCOMM tty teardown race

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Message-Id: <1391997564-1805-10-git-send-email-peter@hurleysoftware.com>
Date:	Sun,  9 Feb 2014 20:59:09 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	Gustavo Padovan <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	Gianluca Anzolin <gianluca@...tospazio.it>,
	Alexander Holler <holler@...oftware.de>,
	Andrey Vihrov <andrey.vihrov@...il.com>,
	Sander Eikelenboom <linux@...elenboom.it>,
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 09/24] Bluetooth: Fix RFCOMM tty teardown race

RFCOMM tty device teardown can race with new tty device registration
for the same device id:

CPU 0                           | CPU 1
rfcomm_dev_add                  | rfcomm_dev_destruct
                                |   spin_lock
                                |   list_del   <== dev_id no longer used
                                |   spin_unlock
  spin_lock                     |     .
  [search rfcomm_dev_list]      |     .
  [dev_id not in use]           |     .
  [initialize new rfcomm_dev]   |     .
  spin_unlock                   |     .
                                |     .
  tty_port_register_device      |   tty_unregister_device

Don't remove rfcomm_dev from the device list until after tty device
unregistration has completed.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 net/bluetooth/rfcomm/tty.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index bb570d9..6ea08b0 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -84,10 +84,6 @@ static void rfcomm_dev_destruct(struct tty_port *port)
 
 	BT_DBG("dev %p dlc %p", dev, dlc);
 
-	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 */
 	if (dlc->owner == dev)
@@ -98,6 +94,10 @@ static void rfcomm_dev_destruct(struct tty_port *port)
 
 	tty_unregister_device(rfcomm_tty_driver, dev->id);
 
+	spin_lock(&rfcomm_dev_lock);
+	list_del(&dev->list);
+	spin_unlock(&rfcomm_dev_lock);
+
 	kfree(dev);
 
 	/* It's safe to call module_put() here because socket still
-- 
1.8.1.2

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