linux-kernel - [PATCH AUTOSEL for 4.14 061/135] Bluetooth: hci_ldisc: Fix another race when closing the tty.

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Message-ID: <20171207154513.4154-61-alexander.levin@verizon.com>
Date:   Thu, 7 Dec 2017 15:45:45 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Ronald Tschalär <ronald@...ovation.ch>,
        "Marcel Holtmann" <marcel@...tmann.org>,
        alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.14 061/135] Bluetooth: hci_ldisc: Fix another
 race when closing the tty.

From: Ronald Tschalär <ronald@...ovation.ch>

[ Upstream commit 0338b1b393ec7910898e8f7b25b3bf31a7282e16 ]

The following race condition still existed:

         P1                                P2
  cancel_work_sync()
                                     hci_uart_tx_wakeup()
                                     hci_uart_write_work()
                                     hci_uart_dequeue()
  clear_bit(HCI_UART_PROTO_READY)
  hci_unregister_dev(hdev)
  hci_free_dev(hdev)
  hu->proto->close(hu)
  kfree(hu)
                                     access to hdev and hu

Cancelling the work after clearing the HCI_UART_PROTO_READY bit avoids
this as any hci_uart_tx_wakeup() issued after the flag is cleared will
detect that and not schedule further work.

Signed-off-by: Ronald Tschalär <ronald@...ovation.ch>
Reviewed-by: Lukas Wunner <lukas@...ner.de>
Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 drivers/bluetooth/hci_ldisc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index a746627e784e..6e2403805784 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -510,13 +510,13 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 	if (hdev)
 		hci_uart_close(hdev);
 
-	cancel_work_sync(&hu->write_work);
-
 	if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
 		write_lock_irqsave(&hu->proto_lock, flags);
 		clear_bit(HCI_UART_PROTO_READY, &hu->flags);
 		write_unlock_irqrestore(&hu->proto_lock, flags);
 
+		cancel_work_sync(&hu->write_work);
+
 		if (hdev) {
 			if (test_bit(HCI_UART_REGISTERED, &hu->flags))
 				hci_unregister_dev(hdev);
-- 
2.11.0