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From:   Sonny Sasaka <sonnysasaka@chromium.org>
To:     linux-bluetooth@vger.kernel.org
Cc:     Sonny Sasaka <sonnysasaka@chromium.org>,
        Miao-chen Chou <mcchou@chromium.org>
Subject: [PATCH BlueZ] device: Fix race condition between device connection and disconnection
Date:   Fri, 21 Aug 2020 00:45:12 -0700
Message-Id: <20200821074512.19985-1-sonnysasaka@chromium.org>
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Sender: linux-bluetooth-owner@vger.kernel.org
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When Connect() is called and waiting for return, dev_disconnected may be
called due to MGMT_EV_DEVICE_DISCONNECTED event from kernel. In that
case reply to client that the connection failed otherwise the dbus
method will timeout because bluetoothd never replies.

Tested with simulation of a lot of Connect() to bluetooth devices and
check that error is returned from bluetoothd rather than dbus timeout
when this race condition happens.

Reviewed-by: Miao-chen Chou <mcchou@chromium.org>

---
 src/device.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/device.c b/src/device.c
index 7b7808405..55e7b4042 100644
--- a/src/device.c
+++ b/src/device.c
@@ -3006,6 +3006,7 @@ void device_add_connection(struct btd_device *dev, uint8_t bdaddr_type)
 void device_remove_connection(struct btd_device *device, uint8_t bdaddr_type)
 {
 	struct bearer_state *state = get_state(device, bdaddr_type);
+	DBusMessage *reply;
 
 	if (!state->connected)
 		return;
@@ -3020,6 +3021,17 @@ void device_remove_connection(struct btd_device *device, uint8_t bdaddr_type)
 		device->disconn_timer = 0;
 	}
 
+	// This could be executed while the client is waiting for Connect() but
+	// att_connect_cb has not been invoked.
+	// In that case reply the client that the connection failed.
+	if (device->connect) {
+		DBG("connection removed while Connect() is waiting reply");
+		reply = btd_error_failed(device->connect, "Disconnected early");
+		g_dbus_send_message(dbus_conn, reply);
+		dbus_message_unref(device->connect);
+		device->connect = NULL;
+	}
+
 	while (device->disconnects) {
 		DBusMessage *msg = device->disconnects->data;
 
-- 
2.26.2