linux-kernel - [PATCH 4.1 015/267] Bluetooth: Fix race condition with user channel and setup stage

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Message-Id: <20150731194002.424120035@linuxfoundation.org>
Date:	Fri, 31 Jul 2015 12:37:46 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>,
	Johan Hedberg <johan.hedberg@...el.com>
Subject: [PATCH 4.1 015/267] Bluetooth: Fix race condition with user channel and setup stage

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marcel Holtmann <marcel@...tmann.org>

commit 781f899f2f9d8b71e35225a087f90052059486c5 upstream.

During the initial setup stage of a controller, the low-level transport
is actually active. This means that HCI_UP is true. To avoid toggling
the transport off and back on again for normal operation the kernel
holds a grace period with HCI_AUTO_OFF that will turn the low-level
transport off in case no user is present.

The idea of the grace period is important to avoid having to initialize
all of the controller twice. So legacy ioctl and the new management
interface knows how to clear this grace period and then start normal
operation.

For the user channel operation this grace period has not been taken into
account which results in the problem that HCI_UP and HCI_AUTO_OFF are
set and the kernel will return EBUSY. However from a system point of
view the controller is ready to be grabbed by either the ioctl, the
management interface or the user channel.

This patch brings the user channel to the same level as the other two
entries for operating a controller.

Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/bluetooth/hci_sock.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -741,10 +741,11 @@ static int hci_sock_bind(struct socket *
 			goto done;
 		}

-		if (test_bit(HCI_UP, &hdev->flags) ||
-		    test_bit(HCI_INIT, &hdev->flags) ||
+		if (test_bit(HCI_INIT, &hdev->flags) ||
 		    hci_dev_test_flag(hdev, HCI_SETUP) ||
-		    hci_dev_test_flag(hdev, HCI_CONFIG)) {
+		    hci_dev_test_flag(hdev, HCI_CONFIG) ||
+		    (!hci_dev_test_flag(hdev, HCI_AUTO_OFF) &&
+		     test_bit(HCI_UP, &hdev->flags))) {
 			err = -EBUSY;
 			hci_dev_put(hdev);
 			goto done;
@@ -760,10 +761,21 @@ static int hci_sock_bind(struct socket *

 		err = hci_dev_open(hdev->id);
 		if (err) {
-			hci_dev_clear_flag(hdev, HCI_USER_CHANNEL);
-			mgmt_index_added(hdev);
-			hci_dev_put(hdev);
-			goto done;
+			if (err == -EALREADY) {
+				/* In case the transport is already up and
+				 * running, clear the error here.
+				 *
+				 * This can happen when opening an user
+				 * channel and HCI_AUTO_OFF grace period
+				 * is still active.
+				 */
+				err = 0;
+			} else {
+				hci_dev_clear_flag(hdev, HCI_USER_CHANNEL);
+				mgmt_index_added(hdev);
+				hci_dev_put(hdev);
+				goto done;
+			}
 		}

 		atomic_inc(&hdev->promisc);

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