Re: [PATCHv1] Bluetooth: Add refcnt to l2cap_conn

Mat Martineau <mathewm@xxxxxxxxxxxxxx> · Fri, 8 Jun 2012 09:54:36 -0700 (PDT)

Andrei -

On Thu, 7 Jun 2012, Andrei Emeltchenko wrote:

From: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>

Adding kref to l2cap_conn helps to better handle racing when deleting
l2cap_conn. Races are created when deleting conn from timeout and from
the other execution path.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>
---
	PATCHv1: fixes issues with LE

include/net/bluetooth/l2cap.h |    6 +++
net/bluetooth/l2cap_core.c    |   94 +++++++++++++++++++++++++++++++++++------
net/bluetooth/smp.c           |    7 ++-
3 files changed, 91 insertions(+), 16 deletions(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 3d31ecd..5abfe8a 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -572,6 +572,8 @@ struct l2cap_conn {

	struct list_head	chan_l;
	struct mutex		chan_lock;
+
+	struct kref		kref;
};

#define L2CAP_INFO_CL_MTU_REQ_SENT	0x01
@@ -779,5 +781,9 @@ void l2cap_chan_set_defaults(struct l2cap_chan *chan);
int l2cap_ertm_init(struct l2cap_chan *chan);
void l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan);
void l2cap_chan_del(struct l2cap_chan *chan, int err);
+void l2cap_conn_set_timer(struct l2cap_conn *conn, struct delayed_work *work,
+			  long timeout);
+bool l2cap_conn_clear_timer(struct l2cap_conn *conn,
+			    struct delayed_work *work);

#endif /* __L2CAP_H */
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index eb7094c..d8c320b 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -57,6 +57,64 @@ static void l2cap_send_disconn_req(struct l2cap_conn *conn,

static void l2cap_tx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
		    struct sk_buff_head *skbs, u8 event);
+static void l2cap_conn_del(struct hci_conn *hcon, int err);
+
+/* ---- L2CAP connections ---- */
+
+static void l2cap_conn_get(struct l2cap_conn *conn)
+{
+	BT_DBG("conn %p", conn);
+
+	kref_get(&conn->kref);
+}
+
+static void l2cap_conn_destroy(struct kref *kref)
+{
+	struct l2cap_conn *conn = container_of(kref, struct l2cap_conn, kref);
+
+	BT_DBG("conn %p", conn);
+
+	l2cap_conn_del(conn->hcon, 0);
+}
+
+static int l2cap_conn_put(struct l2cap_conn *conn)
+{
+	BT_DBG("conn %p", conn);
+
+	/* conn might be NULL, was checked before in l2cap_conn_del */
+	if (!conn)
+		return 1;
+
+	return kref_put(&conn->kref, &l2cap_conn_destroy);
+}
+
+void l2cap_conn_set_timer(struct l2cap_conn *conn, struct delayed_work *work,
+			  long timeout)
+{
+	BT_DBG("conn %p timeout %ld", conn, timeout);
+
+	/* If delayed work cancelled do not hold(conn)
+	   since it is already done with previous set_timer */
+	if (!cancel_delayed_work(work))
+		l2cap_conn_get(conn);
+
+	schedule_delayed_work(work, timeout);
+}
+
+bool l2cap_conn_clear_timer(struct l2cap_conn *conn, struct delayed_work *work)
+{
+	bool ret;
+
+	BT_DBG("conn %p", conn);
+
+	/* put(conn) if delayed work cancelled otherwise it
+	   is done in delayed work function */
+	ret = cancel_delayed_work(work);
+	if (ret)
+		l2cap_conn_put(conn);
+
+	return ret;
+}

/* ---- L2CAP channels ---- */

@@ -1321,10 +1379,8 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
	if (conn->info_state & L2CAP_INFO_FEAT_MASK_REQ_SENT)
		cancel_delayed_work_sync(&conn->info_timer);

-	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &hcon->flags)) {
-		cancel_delayed_work_sync(&conn->security_timer);
+	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &hcon->flags))
		smp_chan_destroy(conn);
-	}

	hcon->l2cap_data = NULL;
	kfree(conn);
@@ -1333,9 +1389,9 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
static void security_timeout(struct work_struct *work)
{
	struct l2cap_conn *conn = container_of(work, struct l2cap_conn,
-						security_timer.work);
+					       security_timer.work);

-	l2cap_conn_del(conn->hcon, ETIMEDOUT);
+	l2cap_conn_put(conn);
}

static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)
@@ -1377,6 +1433,8 @@ static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)

	INIT_LIST_HEAD(&conn->chan_l);

+	kref_init(&conn->kref);
+
	if (hcon->type == LE_LINK)
		INIT_DELAYED_WORK(&conn->security_timer, security_timeout);
	else
@@ -5286,8 +5344,10 @@ static void l2cap_recv_frame(struct l2cap_conn *conn, struct sk_buff *skb)
		break;

	case L2CAP_CID_SMP:
-		if (smp_sig_channel(conn, skb))
-			l2cap_conn_del(conn->hcon, EACCES);
+		if (smp_sig_channel(conn, skb)) {
+			l2cap_conn_clear_timer(conn, &conn->security_timer);
+			l2cap_conn_put(conn);
+		}
		break;

	default:
@@ -5331,7 +5391,7 @@ int l2cap_connect_ind(struct hci_dev *hdev, bdaddr_t *bdaddr)

int l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
{
-	struct l2cap_conn *conn;
+	struct l2cap_conn *conn = hcon->l2cap_data;

	BT_DBG("hcon %p bdaddr %s status %d", hcon, batostr(&hcon->dst), status);

@@ -5339,8 +5399,12 @@ int l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
		conn = l2cap_conn_add(hcon, status);
		if (conn)
			l2cap_conn_ready(conn);
-	} else
-		l2cap_conn_del(hcon, bt_to_errno(status));
+	} else {
+		if (hcon->type == LE_LINK)
+			l2cap_conn_clear_timer(conn, &conn->security_timer);
+
+		l2cap_conn_put(conn);
+	}

	return 0;
}
@@ -5358,9 +5422,14 @@ int l2cap_disconn_ind(struct hci_conn *hcon)

int l2cap_disconn_cfm(struct hci_conn *hcon, u8 reason)
{
+	struct l2cap_conn *conn = hcon->l2cap_data;
	BT_DBG("hcon %p reason %d", hcon, reason);

-	l2cap_conn_del(hcon, bt_to_errno(reason));
+	if (hcon->type == LE_LINK)
+		l2cap_conn_clear_timer(conn, &conn->security_timer);
+
+	l2cap_conn_put(conn);
+
	return 0;
}

@@ -5393,7 +5462,8 @@ int l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
	if (hcon->type == LE_LINK) {
		if (!status && encrypt)
			smp_distribute_keys(conn, 0);
-		cancel_delayed_work(&conn->security_timer);
+
+		l2cap_conn_clear_timer(conn, &conn->security_timer);
	}

	mutex_lock(&conn->chan_lock);
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index ff4835b..7aaf849 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -186,8 +186,7 @@ static void smp_send_cmd(struct l2cap_conn *conn, u8 code, u16 len, void *data)
	skb->priority = HCI_PRIO_MAX;
	hci_send_acl(conn->hchan, skb, 0);

-	cancel_delayed_work_sync(&conn->security_timer);
-	schedule_delayed_work(&conn->security_timer, SMP_TIMEOUT);
+	l2cap_conn_set_timer(conn, &conn->security_timer, SMP_TIMEOUT);
}

static __u8 authreq_to_seclevel(__u8 authreq)
@@ -268,7 +267,7 @@ static void smp_failure(struct l2cap_conn *conn, u8 reason, u8 send)
			 hcon->dst_type, reason);

	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->flags)) {
-		cancel_delayed_work_sync(&conn->security_timer);
+		l2cap_conn_clear_timer(conn, &conn->security_timer);
		smp_chan_destroy(conn);
	}
}
@@ -996,7 +995,7 @@ int smp_distribute_keys(struct l2cap_conn *conn, __u8 force)

	if (conn->hcon->out || force) {
		clear_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->flags);
-		cancel_delayed_work_sync(&conn->security_timer);
+		l2cap_conn_clear_timer(conn, &conn->security_timer);
		smp_chan_destroy(conn);
	}

--
1.7.9.5

I think it's a very good thing to add reference counting, thanks for 
doing this work.

I'd like to see the code be more strict about matching the gets & puts 
up with actual assignments to l2cap_conn pointers:

 * Make sure one reference count is held for hcon->l2cap_data (your 
patch already does this)
 * l2cap_conn_put when setting hcon->l2cap_data to NULL
 * l2cap_conn_get when assigning l2cap_chan->conn
 * l2cap_conn_put when setting l2cap_chan->conn to NULL or freeing 
l2cap_chan
 * Use l2cap_conn_get/put whenever there's a reference to an 
l2cap_conn struct in an active timer.  You set this up for the 
security_timer, but info_timer could use it too.

Right now, l2cap_conn_del is only called when the reference count goes 
to 0.  If l2cap_conn reference counts are added to l2cap_chan, then 
the reference count wouldn't be 0 if the ACL was forced to close, and 
the l2cap_chans would not get cleaned up.  I think it would help to 
make l2cap_conn_del clean up the channels and connection state, and 
then have l2cap_conn_destroy free the structure.  l2cap_conn_destroy 
would only have to call l2cap_conn_del if it hadn't been done yet.


Regards,

--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum

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