[PATCH 5.11 002/601] bluetooth: eliminate the potential race condition when removing the HCI controller

Greg Kroah-Hartman
2021-05-12T16:52:37Z

From: Lin Ma <linma@zju.edu.cn>

commit e2cb6b891ad2b8caa9131e3be70f45243df82a80 upstream.

There is a possible race condition vulnerability between issuing a HCI
command and removing the cont. Specifically, functions hci_req_sync()
and hci_dev_do_close() can race each other like below:

thread-A in hci_req_sync() | thread-B in hci_dev_do_close()
| hci_req_sync_lock(hdev);
test_bit(HCI_UP, &hdev->flags); |
... | test_and_clear_bit(HCI_UP, &hdev->flags)
hci_req_sync_lock(hdev); |
|
In this commit we alter the sequence in function hci_req_sync(). Hence,
the thread-A cannot issue th.

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Cc: Marcel Holtmann <marcel@holtmann.org>
Fixes: 7c6a329e4447 ("[Bluetooth] Fix regression from using default link policy")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/bluetooth/hci_request.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/net/bluetooth/hci_request.c
+++ b/net/bluetooth/hci_request.c
@@ -271,12 +271,16 @@ int hci_req_sync(struct hci_dev *hdev, i
{
int ret;

- if (!test_bit(HCI_UP, &hdev->flags))
- return -ENETDOWN;
-
/* Serialize all requests */
hci_req_sync_lock(hdev);
- ret = __hci_req_sync(hdev, req, opt, timeout, hci_status);
+ /* check the state after obtaing the lock to protect the HCI_UP
+ * against any races from hci_dev_do_close when the controller
+ * gets removed.
+ */
+ if (test_bit(HCI_UP, &hdev->flags))
+ ret = __hci_req_sync(hdev, req, opt, timeout, hci_status);
+ else
+ ret = -ENETDOWN;
hci_req_sync_unlock(hdev);

return ret;