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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lin Ma <linma@zju.edu.cn>,
        Marcel Holtmann <marcel@holtmann.org>
Subject: [PATCH 5.12 002/677] bluetooth: eliminate the potential race condition when removing the HCI controller
Date:   Wed, 12 May 2021 16:40:48 +0200
Message-Id: <20210512144837.290499032@linuxfoundation.org>
In-Reply-To: <20210512144837.204217980@linuxfoundation.org>
References: <20210512144837.204217980@linuxfoundation.org>
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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
@@ -272,12 +272,16 @@ 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;