linux-kernel - [PATCH AUTOSEL for 4.9 124/190] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx

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Date:   Thu, 8 Mar 2018 04:59:46 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Dean Jenkins <Dean_Jenkins@...tor.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.9 124/190] Bluetooth: hci_ldisc: Add protocol
 check to hci_uart_tx_wakeup()

From: Dean Jenkins <Dean_Jenkins@...tor.com>

[ Upstream commit 2d6f1da168e1d62c47f7d50135ac4cbd8411dcb1 ]

Before attempting to schedule a work-item onto hu->write_work in
hci_uart_tx_wakeup(), check that the Data Link protocol layer is
still bound to the HCI UART driver.

Failure to perform this protocol check causes a race condition between
the work queue hu->write_work running hci_uart_write_work() and the
Data Link protocol layer being unbound (closed) in hci_uart_tty_close().

Note hci_uart_tty_close() does have a "cancel_work_sync(&hu->write_work)"
but it is ineffective because it cannot prevent work-items being added
to hu->write_work after cancel_work_sync() has run.

Therefore, add a check for HCI_UART_PROTO_READY into hci_uart_tx_wakeup()
which prevents scheduling of the work queue when HCI_UART_PROTO_READY
is in the clear state. However, note a small race condition remains
because the hci_uart_tx_wakeup() thread can run in parallel with the
hci_uart_tty_close() thread so it is possible that a schedule of
hu->write_work can occur when HCI_UART_PROTO_READY is cleared. A complete
solution needs locking of the threads which is implemented in a future
commit.

Signed-off-by: Dean Jenkins <Dean_Jenkins@...tor.com>
Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/bluetooth/hci_ldisc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 7ec73945351c..2230f9368c21 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -125,6 +125,9 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)

 int hci_uart_tx_wakeup(struct hci_uart *hu)
 {
+	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags))
+		return 0;
+
 	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
 		set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
 		return 0;
-- 
2.14.1