linux-kernel - [PATCH 4.4 53/54] bluetooth: eliminate the potential race condition when removing the HCI controller

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Message-Id: <20210531130636.726513004@linuxfoundation.org>
Date:   Mon, 31 May 2021 15:14:19 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lin Ma <linma@....edu.cn>,
        Marcel Holtmann <marcel@...tmann.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
Subject: [PATCH 4.4 53/54] bluetooth: eliminate the potential race condition when removing the HCI controller

From: Lin Ma <linma@....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@....edu.cn>
Cc: Marcel Holtmann <marcel@...tmann.org>
Fixes: 7c6a329e4447 ("[Bluetooth] Fix regression from using default link policy")
[iwamatsu: adjust filename, arguments of __hci_req_sync(). CVE-2021-32399]
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/bluetooth/hci_core.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -371,12 +371,17 @@ static int hci_req_sync(struct hci_dev *
 {
 	int ret;
 
-	if (!test_bit(HCI_UP, &hdev->flags))
-		return -ENETDOWN;
-
 	/* Serialize all requests */
 	hci_req_lock(hdev);
-	ret = __hci_req_sync(hdev, req, opt, timeout);
+	/* 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);
+	else
+		ret = -ENETDOWN;
+
 	hci_req_unlock(hdev);
 
 	return ret;