By setting the bit RFCOMM_TTY_RELEASED in the dev->flags we prevent the code to
take any reference to the device. This way we can unnest the rfcomm_dev_lock and
the rfcomm_dlc_lock in rfcomm_dev_add().
In rfcomm_dev_state_change we can now take a reference to the device without
having to drop the dlc lock: this way we ensure the dev cannot be used after
being freed.
Signed-off-by: Gianluca Anzolin <gianluca@xxxxxxxxxxxxxx>
---
net/bluetooth/rfcomm/tty.c | 67 ++++++++++++++++++++++++----------------------
1 file changed, 35 insertions(+), 32 deletions(-)
diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 50b38d7..6ae7882e 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -196,6 +196,9 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
if (!dev)
return -ENOMEM;
+ /* avoid taking references to dev if not initialized */
+ set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
+
spin_lock(&rfcomm_dev_lock);
if (req->dev_id < 0) {
@@ -233,6 +236,8 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
list_add(&dev->list, head);
+ spin_unlock(&rfcomm_dev_lock);
+
bacpy(&dev->src, &req->src);
bacpy(&dev->dst, &req->dst);
dev->channel = req->channel;
@@ -277,19 +282,25 @@ static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)
holds reference to this module. */
__module_get(THIS_MODULE);
-out:
- spin_unlock(&rfcomm_dev_lock);
-
- if (err < 0)
- goto free;
-
dev->tty_dev = tty_port_register_device(&dev->port, rfcomm_tty_driver,
dev->id, NULL);
if (IS_ERR(dev->tty_dev)) {
err = PTR_ERR(dev->tty_dev);
+
+ module_put(THIS_MODULE);
+
spin_lock(&rfcomm_dev_lock);
list_del(&dev->list);
spin_unlock(&rfcomm_dev_lock);
+
+ skb_queue_purge(&dev->pending);
+
+ rfcomm_dlc_lock(dlc);
+ dlc->data_ready = NULL;
+ dlc->state_change = NULL;
+ dlc->modem_status = NULL;
+ dlc->owner = NULL;
+ rfcomm_dlc_unlock(dlc);
goto free;
}
@@ -301,8 +312,12 @@ out:
if (device_create_file(dev->tty_dev, &dev_attr_channel) < 0)
BT_ERR("Failed to create channel attribute");
- return dev->id;
+ /* the device is initialized, we can take references to it */
+ clear_bit(RFCOMM_TTY_RELEASED, &dev->flags);
+ return dev->id;
+out:
+ spin_unlock(&rfcomm_dev_lock);
free:
kfree(dev);
return err;
@@ -585,33 +600,21 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err)
wake_up_interruptible(&dev->port.open_wait);
} else if (dlc->state == BT_CLOSED) {
tty = tty_port_tty_get(&dev->port);
- if (!tty) {
- if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
- /* Drop DLC lock here to avoid deadlock
- * 1. rfcomm_dev_get will take rfcomm_dev_lock
- * but in rfcomm_dev_add there's lock order:
- * rfcomm_dev_lock -> dlc lock
- * 2. tty_port_put will deadlock if it's
- * the last reference
- *
- * FIXME: when we release the lock anything
- * could happen to dev, even its destruction
- */
- rfcomm_dlc_unlock(dlc);
- if (rfcomm_dev_get(dev->id) == NULL) {
- rfcomm_dlc_lock(dlc);
- return;
- }
-
- set_bit(RFCOMM_TTY_RELEASED, &dev->flags);
- tty_port_put(&dev->port);
-
- tty_port_put(&dev->port);
- rfcomm_dlc_lock(dlc);
- }
- } else {
+ if (tty) {
tty_hangup(tty);
tty_kref_put(tty);
+ } else if (!test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags))
+ ;
+ else if (rfcomm_dev_get(dev->id)) {
+ if (!test_and_set_bit(RFCOMM_TTY_RELEASED, &dev->flags))
+ tty_port_put(&dev->port);
+
+ /* tty_port_put will deadlock if it is
+ * the last reference
+ */
+ rfcomm_dlc_unlock(dlc);
+ tty_port_put(&dev->port);
+ rfcomm_dlc_lock(dlc);
}
}
}
--
1.8.3.3
--
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