[PATCH 15/24] Bluetooth: Fix unsafe RFCOMM device parenting

Peter Hurley
2014-02-10T02:20:18Z

Accessing the results of hci_conn_hash_lookup_ba() is unsafe without
holding the hci_dev_lock() during the lookup. For example:

CPU 0 | CPU 1
hci_conn_hash_lookup_ba | hci_conn_del
rcu_read_lock | hci_conn_hash_del
list_for_each_entry_rcu | list_del_rcu
if (.....) | synchronize_rcu
rcu_read_unlock |
| hci_conn_del_sysfs
| hci_dev_put
| hci_conn_put
| put_device (last reference)
| bt_link_release
| kfree(conn)
return p << just freed |

Even if a hci_conn reference were taken (via hci_conn_get), would
not guarantee the lifetime of the sysfs device, but only safe
access to the in-memory structure.

Ensure the hci_conn device stays valid while the rfcomm device
is reparented; rename rfcomm_get_device() to rfcomm_reparent_device()
and perform the reparenting within the function while holding the
hci_dev_lock.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
net/bluetooth/rfcomm/tty.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index a58d693..2975bc4 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -167,20 +167,29 @@ static struct rfcomm_dev *rfcomm_dev_get(int id)
return dev;
}

-static struct device *rfcomm_get_device(struct rfcomm_dev *dev)
+static void rfcomm_reparent_device(struct rfcomm_dev *dev)
{
struct hci_dev *hdev;
struct hci_conn *conn;

hdev = hci_get_route(&dev->dst, &dev->src);
if (!hdev)
- return NULL;
+ return;

+ /* The lookup results are unsafe to access without the
+ * hci device lock (FIXME: why is this not documented?)
+ */
+ hci_dev_lock(hdev);
conn = hci_conn_hash_lookup_ba(hdev, ACL_LINK, &dev->dst);

- hci_dev_put(hdev);
+ /* Just because the acl link is in the hash table is no
+ * guarantee the sysfs device has been added ...
+ */
+ if (conn && device_is_registered(&conn->dev))
+ device_move(dev->tty_dev, &conn->dev, DPM_ORDER_DEV_AFTER_PARENT);

- return conn ? &conn->dev : NULL;
+ hci_dev_unlock(hdev);
+ hci_dev_put(hdev);
}

static ssize_t show_address(struct device *tty_dev, struct device_attribute *attr, char *buf)
@@ -589,8 +598,7 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)

dev->err = err;
if (dlc->state == BT_CONNECTED) {
- device_move(dev->tty_dev, rfcomm_get_device(dev),
- DPM_ORDER_DEV_AFTER_PARENT);
+ rfcomm_reparent_device(dev);

wake_up_interruptible(&dev->port.open_wait);
} else if (dlc->state == BT_CLOSED)
--
1.8.1.2