Commit 2350cffd authored Nov 16, 2021 by Lin Ma Committed by Greg Kroah-Hartman Dec 01, 2021

NFC: add NCI_UNREG flag to eliminate the race



commit 48b71a9e66c2eab60564b1b1c85f4928ed04e406 upstream.

There are two sites that calls queue_work() after the
destroy_workqueue() and lead to possible UAF.

The first site is nci_send_cmd(), which can happen after the
nci_close_device as below

nfcmrvl_nci_unregister_dev   |  nfc_genl_dev_up
  nci_close_device           |
    flush_workqueue          |
    del_timer_sync           |
  nci_unregister_device      |    nfc_get_device
    destroy_workqueue        |    nfc_dev_up
    nfc_unregister_device    |      nci_dev_up
      device_del             |        nci_open_device
                             |          __nci_request
                             |            nci_send_cmd
                             |              queue_work !!!

Another site is nci_cmd_timer, awaked by the nci_cmd_work from the
nci_send_cmd.

  ...                        |  ...
  nci_unregister_device      |  queue_work
    destroy_workqueue        |
    nfc_unregister_device    |  ...
      device_del             |  nci_cmd_work
                             |  mod_timer
                             |  ...
                             |  nci_cmd_timer
                             |    queue_work !!!

For the above two UAF, the root cause is that the nfc_dev_up can race
between the nci_unregister_device routine. Therefore, this patch
introduce NCI_UNREG flag to easily eliminate the possible race. In
addition, the mutex_lock in nci_close_device can act as a barrier.

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Fixes: 6a2968aa ("NFC: basic NCI protocol implementation")
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211116152732.19238-1-linma@zju.edu.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b0313bc7

include/net/nfc/nci_core.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -42,6 +42,7 @@ enum nci_flag {
		NCI_UP,
		NCI_DATA_EXCHANGE,
		NCI_DATA_EXCHANGE_TO,
		NCI_UNREG,
		};

		/* NCI device states */

net/nfc/nci/core.c

+17 −2

Original line number	Diff line number	Diff line
		@@ -485,6 +485,11 @@ static int nci_open_device(struct nci_dev *ndev)

		mutex_lock(&ndev->req_lock);

		if (test_bit(NCI_UNREG, &ndev->flags)) {
		rc = -ENODEV;
		goto done;
		}

		if (test_bit(NCI_UP, &ndev->flags)) {
		rc = -EALREADY;
		goto done;
		@@ -548,6 +553,10 @@ static int nci_open_device(struct nci_dev *ndev)
		static int nci_close_device(struct nci_dev *ndev)
		{
		nci_req_cancel(ndev, ENODEV);

		/* This mutex needs to be held as a barrier for
		* caller nci_unregister_device
		*/
		mutex_lock(&ndev->req_lock);

		if (!test_and_clear_bit(NCI_UP, &ndev->flags)) {
		@@ -585,8 +594,8 @@ static int nci_close_device(struct nci_dev *ndev)
		/* Flush cmd wq */
		flush_workqueue(ndev->cmd_wq);

		/* Clear flags */
		ndev->flags = 0;
		/* Clear flags except NCI_UNREG */
		ndev->flags &= BIT(NCI_UNREG);

		mutex_unlock(&ndev->req_lock);

		@@ -1268,6 +1277,12 @@ void nci_unregister_device(struct nci_dev *ndev)
		{
		struct nci_conn_info conn_info, n;

		/* This set_bit is not protected with specialized barrier,
		* However, it is fine because the mutex_lock(&ndev->req_lock);
		* in nci_close_device() will help to emit one.
		*/
		set_bit(NCI_UNREG, &ndev->flags);

		nci_close_device(ndev);

		destroy_workqueue(ndev->cmd_wq);