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Subject[PATCH 4.3 077/125] Bluetooth: Fix missing hdev locking for LE scan cleanup
Date
4.3-stable review patch.  If anyone has any objections, please let me know.

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

From: Johan Hedberg <johan.hedberg@intel.com>

commit 8ce783dc5ea3af3a213ac9b4d9d2ccfeeb9c9058 upstream.

The hci_conn objects don't have a dedicated lock themselves but rely
on the caller to hold the hci_dev lock for most types of access. The
hci_conn_timeout() function has so far sent certain HCI commands based
on the hci_conn state which has been possible without holding the
hci_dev lock.

The recent changes to do LE scanning before connect attempts added
even more operations to hci_conn and hci_dev from hci_conn_timeout,
thereby exposing potential race conditions with the hci_dev and
hci_conn states.

As an example of such a race, here there's a timeout but an
l2cap_sock_connect() call manages to race with the cleanup routine:

[Oct21 08:14] l2cap_chan_timeout: chan ee4b12c0 state BT_CONNECT
[ +0.000004] l2cap_chan_close: chan ee4b12c0 state BT_CONNECT
[ +0.000002] l2cap_chan_del: chan ee4b12c0, conn f3141580, err 111, state BT_CONNECT
[ +0.000002] l2cap_sock_teardown_cb: chan ee4b12c0 state BT_CONNECT
[ +0.000005] l2cap_chan_put: chan ee4b12c0 orig refcnt 4
[ +0.000010] hci_conn_drop: hcon f53d56e0 orig refcnt 1
[ +0.000013] l2cap_chan_put: chan ee4b12c0 orig refcnt 3
[ +0.000063] hci_conn_timeout: hcon f53d56e0 state BT_CONNECT
[ +0.000049] hci_conn_params_del: addr ee:0d:30:09:53:1f (type 1)
[ +0.000002] hci_chan_list_flush: hcon f53d56e0
[ +0.000001] hci_chan_del: hci0 hcon f53d56e0 chan f4e7ccc0
[ +0.004528] l2cap_sock_create: sock e708fc00
[ +0.000023] l2cap_chan_create: chan ee4b1770
[ +0.000001] l2cap_chan_hold: chan ee4b1770 orig refcnt 1
[ +0.000002] l2cap_sock_init: sk ee4b3390
[ +0.000029] l2cap_sock_bind: sk ee4b3390
[ +0.000010] l2cap_sock_setsockopt: sk ee4b3390
[ +0.000037] l2cap_sock_connect: sk ee4b3390
[ +0.000002] l2cap_chan_connect: 00:02:72:d9:e5:8b -> ee:0d:30:09:53:1f (type 2) psm 0x00
[ +0.000002] hci_get_route: 00:02:72:d9:e5:8b -> ee:0d:30:09:53:1f
[ +0.000001] hci_dev_hold: hci0 orig refcnt 8
[ +0.000003] hci_conn_hold: hcon f53d56e0 orig refcnt 0

Above the l2cap_chan_connect() shouldn't have been able to reach the
hci_conn f53d56e0 anymore but since hci_conn_timeout didn't do proper
locking that's not the case. The end result is a reference to hci_conn
that's not in the conn_hash list, resulting in list corruption when
trying to remove it later:

[Oct21 08:15] l2cap_chan_timeout: chan ee4b1770 state BT_CONNECT
[ +0.000004] l2cap_chan_close: chan ee4b1770 state BT_CONNECT
[ +0.000003] l2cap_chan_del: chan ee4b1770, conn f3141580, err 111, state BT_CONNECT
[ +0.000001] l2cap_sock_teardown_cb: chan ee4b1770 state BT_CONNECT
[ +0.000005] l2cap_chan_put: chan ee4b1770 orig refcnt 4
[ +0.000002] hci_conn_drop: hcon f53d56e0 orig refcnt 1
[ +0.000015] l2cap_chan_put: chan ee4b1770 orig refcnt 3
[ +0.000038] hci_conn_timeout: hcon f53d56e0 state BT_CONNECT
[ +0.000003] hci_chan_list_flush: hcon f53d56e0
[ +0.000002] hci_conn_hash_del: hci0 hcon f53d56e0
[ +0.000001] ------------[ cut here ]------------
[ +0.000461] WARNING: CPU: 0 PID: 1782 at lib/list_debug.c:56 __list_del_entry+0x3f/0x71()
[ +0.000839] list_del corruption, f53d56e0->prev is LIST_POISON2 (00000200)

The necessary fix is unfortunately more complicated than just adding
hci_dev_lock/unlock calls to the hci_conn_timeout() call path.
Particularly, the hci_conn_del() API, which expects the hci_dev lock to
be held, performs a cancel_delayed_work_sync(&hcon->disc_work) which
would lead to a deadlock if the hci_conn_timeout() call path tries to
acquire the same lock.

This patch solves the problem by deferring the cleanup work to a
separate work callback. To protect against the hci_dev or hci_conn
going away meanwhile temporary references are taken with the help of
hci_dev_hold() and hci_conn_get().

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/net/bluetooth/hci_core.h | 1
net/bluetooth/hci_conn.c | 50 ++++++++++++++++++++++++++++++++-------
2 files changed, 43 insertions(+), 8 deletions(-)

--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -469,6 +469,7 @@ struct hci_conn {
struct delayed_work auto_accept_work;
struct delayed_work idle_work;
struct delayed_work le_conn_timeout;
+ struct work_struct le_scan_cleanup;

struct device dev;
struct dentry *debugfs;
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -137,18 +137,51 @@ static void hci_conn_cleanup(struct hci_
hci_conn_put(conn);
}

-/* This function requires the caller holds hdev->lock */
+static void le_scan_cleanup(struct work_struct *work)
+{
+ struct hci_conn *conn = container_of(work, struct hci_conn,
+ le_scan_cleanup);
+ struct hci_dev *hdev = conn->hdev;
+ struct hci_conn *c = NULL;
+
+ BT_DBG("%s hcon %p", hdev->name, conn);
+
+ hci_dev_lock(hdev);
+
+ /* Check that the hci_conn is still around */
+ rcu_read_lock();
+ list_for_each_entry_rcu(c, &hdev->conn_hash.list, list) {
+ if (c == conn)
+ break;
+ }
+ rcu_read_unlock();
+
+ if (c == conn) {
+ hci_connect_le_scan_cleanup(conn);
+ hci_conn_cleanup(conn);
+ }
+
+ hci_dev_unlock(hdev);
+ hci_dev_put(hdev);
+ hci_conn_put(conn);
+}
+
static void hci_connect_le_scan_remove(struct hci_conn *conn)
{
- hci_connect_le_scan_cleanup(conn);
+ BT_DBG("%s hcon %p", conn->hdev->name, conn);

- /* We can't call hci_conn_del here since that would deadlock
- * with trying to call cancel_delayed_work_sync(&conn->disc_work).
- * Instead, call just hci_conn_cleanup() which contains the bare
- * minimum cleanup operations needed for a connection in this
- * state.
+ /* We can't call hci_conn_del/hci_conn_cleanup here since that
+ * could deadlock with another hci_conn_del() call that's holding
+ * hci_dev_lock and doing cancel_delayed_work_sync(&conn->disc_work).
+ * Instead, grab temporary extra references to the hci_dev and
+ * hci_conn and perform the necessary cleanup in a separate work
+ * callback.
*/
- hci_conn_cleanup(conn);
+
+ hci_dev_hold(conn->hdev);
+ hci_conn_get(conn);
+
+ schedule_work(&conn->le_scan_cleanup);
}

static void hci_acl_create_connection(struct hci_conn *conn)
@@ -580,6 +613,7 @@ struct hci_conn *hci_conn_add(struct hci
INIT_DELAYED_WORK(&conn->auto_accept_work, hci_conn_auto_accept);
INIT_DELAYED_WORK(&conn->idle_work, hci_conn_idle);
INIT_DELAYED_WORK(&conn->le_conn_timeout, le_conn_timeout);
+ INIT_WORK(&conn->le_scan_cleanup, le_scan_cleanup);

atomic_set(&conn->refcnt, 0);




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