In the Linux kernel, the following vulnerability has been resolved:
nfc: nci: fix double completion race in nci_data_exchange_complete
nci_close_device() and nci_rx_work can both call
nci_data_exchange_complete() concurrently. After commit 4527025d440ce8
("nfc: nci: fix circular locking dependency in nci_close_device") moved
flush_workqueue(ndev->rx_wq) after mutex_unlock(&ndev->req_lock),
rx_work is no longer serialized with the explicit completion call in the
close path. Both callers read the non-NULL callback pointer and invoke
rawsock_data_exchange_complete(), which calls sock_put() -- but only one
sock_hold() was taken, so the second sock_put() underflows the refcount
and frees the socket while it is still in use.
Replace the bare clear_bit(NCI_DATA_EXCHANGE) with
test_and_clear_bit() so that only the first caller proceeds to invoke
the callback.