NFC: add NCI_UNREG flag to eliminate the race

[ Upstream commit 48b71a9e66c2eab60564b1b1c85f4928ed04e406 ]

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: 6a2968aaf50c ("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: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/nfc/nci_core.h b/include/net/nfc/nci_core.h
index a964dae..ea85956 100644 (file)
--- a/include/net/nfc/nci_core.h
+++ b/include/net/nfc/nci_core.h
@@ -30,6 +30,7 @@ enum nci_flag {
        NCI_UP,
        NCI_DATA_EXCHANGE,
        NCI_DATA_EXCHANGE_TO,
+       NCI_UNREG,
 };
 
 /* NCI device states */

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index 39994db..e41e2e9 100644 (file)
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -476,6 +476,11 @@ 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 @@ done:
 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)
 
        del_timer_sync(&ndev->cmd_timer);
 
-       /* Clear flags */
-       ndev->flags = 0;
+       /* Clear flags except NCI_UNREG */
+       ndev->flags &= BIT(NCI_UNREG);
 
        mutex_unlock(&ndev->req_lock);
 
@@ -1273,6 +1282,12 @@ 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);