[PATCH] nfc/nci: fix task hung in nfc_targets_found

[Edward Adam Davis]

nci_start_poll() holds the dev->mutex required by the kworker of nci_close_device(),
and the related tasks are as follows:
|cpu0                          |cpu1                                           |cpu2                      |
|nci_close_device()            |                                               |                          |
|mutex_lock(&ndev->req_lock);  |                                               |                          |
|...                           |nfc_genl_start_poll()                          |                          |
|flush_workqueue(ndev->rx_wq)  |mutex_lock(&dev->genl_data.genl_data_mutex);   |                          |
|                              |nfc_start_poll()                               |                          |
|              	               |device_lock(&dev->dev);                        |process_one_work()        |
|                              |nci_start_poll()                               |nfc_targets_found()       |
|                              |nci_request()                                  |device_lock(&dev->dev);   |
|                              |mutex_lock(&ndev->req_lock);                   |                          |

Therefore, before applying for req_lock in nci_request(), it should be determined
whether the execution of nci_close_device() has already begun.

Reported-and-tested-by: syzbot+2b131f51bb4af224ab40@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 net/nfc/nci/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index 6c9592d05120..9a277228a875 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -145,6 +145,8 @@ inline int nci_request(struct nci_dev *ndev,
 {
 	int rc;
 
+	if (test_bit(NCI_UNREG, &ndev->flags))
+		return -ENODEV;
 	/* Serialize all requests */
 	mutex_lock(&ndev->req_lock);
 	/* check the state after obtaing the lock against any races
-- 
2.43.0