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From: Dean Jenkins <Dean_Jenkins@mentor.com>
To: Marcel Holtmann <marcel@holtmann.org>
Cc: Dean Jenkins <Dean_Jenkins@mentor.com>,
	"Gustavo F . Padovan" <gustavo@padovan.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	<linux-bluetooth@vger.kernel.org>
Subject: [RFC V1 06/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_dequeue()
Date: Tue, 28 Mar 2017 18:50:19 +0100	[thread overview]
Message-ID: <1490723429-28870-7-git-send-email-Dean_Jenkins@mentor.com> (raw)
In-Reply-To: <1490723429-28870-1-git-send-email-Dean_Jenkins@mentor.com>

Before attempting to dequeue a Data Link protocol encapsulated message,
check that the Data Link protocol is still bound to the HCI UART driver.
This makes the code consistent with the usage of the other proto
function pointers.

Therefore, add a check for HCI_UART_PROTO_READY into hci_uart_dequeue()
and return NULL if the Data Link protocol is not bound.

This is needed for robustness as there is a scheduling race condition.
hci_uart_write_work() is scheduled to run via work queue hu->write_work
from hci_uart_tx_wakeup(). Therefore, there is a delay between
scheduling hci_uart_write_work() to run and hci_uart_dequeue() running
whereby the Data Link protocol layer could become unbound during the
scheduling delay. In this case, without the check, the call to the
unbound Data Link protocol layer dequeue function can crash.

It is noted that hci_uart_tty_close() has a
"cancel_work_sync(&hu->write_work)" statement but this only reduces
the window of the race condition because it is possible for a new
work-item to be added to work queue hu->write_work after the call to
cancel_work_sync(). For example, Data Link layer retransmissions can
be added to the work queue after the cancel_work_sync() has finished.

Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
---
 drivers/bluetooth/hci_ldisc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index eeea305..c4b801b 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -113,10 +113,12 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
 {
 	struct sk_buff *skb = hu->tx_skb;
 
-	if (!skb)
-		skb = hu->proto->dequeue(hu);
-	else
+	if (!skb) {
+		if (test_bit(HCI_UART_PROTO_READY, &hu->flags))
+			skb = hu->proto->dequeue(hu);
+	} else {
 		hu->tx_skb = NULL;
+	}
 
 	return skb;
 }
-- 
2.7.4

  parent reply	other threads:[~2017-03-28 17:50 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28 17:50 [RFC V1 00/16] hci_ldisc hci_uart_tty_close() fixes Dean Jenkins
2017-03-28 17:50 ` [RFC V1 01/16] Bluetooth: hci_ldisc: Add missing return in hci_uart_init_work() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 02/16] Bluetooth: hci_ldisc: Ensure hu->hdev set to NULL before freeing hdev Dean Jenkins
2017-03-28 17:50 ` [RFC V1 03/16] Bluetooth: hci_ldisc: Add missing clear HCI_UART_PROTO_READY Dean Jenkins
2017-03-28 17:50 ` [RFC V1 04/16] Bluetooth: hci_ldisc: Add HCI RESET comment to hci_unregister_dev() call Dean Jenkins
2017-03-30 10:11   ` Marcel Holtmann
2017-03-28 17:50 ` [RFC V1 05/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_send_frame() Dean Jenkins
2017-03-28 17:50 ` Dean Jenkins [this message]
2017-03-28 17:50 ` [RFC V1 07/16] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup() Dean Jenkins
2017-03-30 10:11   ` Marcel Holtmann
2017-03-28 17:50 ` [RFC V1 08/16] Bluetooth: hci_ldisc: Separate flag handling in hci_uart_tty_close() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 09/16] Bluetooth: hci_ldisc: Tidy-up HCI_UART_REGISTERED " Dean Jenkins
2017-03-28 17:50 ` [RFC V1 10/16] Bluetooth: hci_ldisc: hci_uart_tty_close() detach tty after last msg Dean Jenkins
2017-03-28 17:50 ` [RFC V1 11/16] Bluetooth: hci_ldisc: hci_uart_tty_close() move hci_uart_close() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 12/16] Bluetooth: hci_ldisc: hci_uart_tty_close() move cancel_work_sync() Dean Jenkins
2017-03-28 17:50 ` [RFC V1 13/16] Bluetooth: hci_ldisc: hci_uart_tty_close() free hu->tx_skb Dean Jenkins
2017-03-28 17:50 ` [RFC V1 14/16] Bluetooth: hci_ldisc: Simplify flushing Dean Jenkins
2017-03-28 17:50 ` [RFC V1 15/16] Bluetooth: hci_ldisc: Use rwlocking to avoid closing proto races Dean Jenkins
2017-03-28 17:50 ` [RFC V1 16/16] Bluetooth: hci_ldisc: Add ioctl_mutex avoiding concurrency Dean Jenkins
2017-03-30 10:11 ` [RFC V1 00/16] hci_ldisc hci_uart_tty_close() fixes Marcel Holtmann
2017-04-03 15:09   ` Dean Jenkins
2017-04-03 15:51     ` Marcel Holtmann
2017-04-04 20:36       ` Dean Jenkins
2017-04-05 15:28         ` Dean Jenkins
2017-04-06  7:23           ` Marcel Holtmann

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