[PATCH net 5/5] nfc: rawsock: cancel tx_work before socket teardown

[Jakub Kicinski <kuba@kernel.org>]

In rawsock_release(), cancel any pending tx_work and purge the write
queue before orphaning the socket.  rawsock_tx_work runs on the system
workqueue and calls nfc_data_exchange which dereferences the NCI
device.  Without synchronization, tx_work can race with socket and
device teardown when a process is killed (e.g. by SIGKILL), leading
to use-after-free or leaked references.

Set SEND_SHUTDOWN first so that if tx_work is already running it will
see the flag and skip transmitting, then use cancel_work_sync to wait
for any in-progress execution to finish, and finally purge any
remaining queued skbs.

Fixes: 23b7869c0fd0 ("NFC: add the NFC socket raw protocol")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/nfc/rawsock.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/nfc/rawsock.c b/net/nfc/rawsock.c
index b049022399ae..f7d7a599fade 100644
--- a/net/nfc/rawsock.c
+++ b/net/nfc/rawsock.c
@@ -67,6 +67,17 @@ static int rawsock_release(struct socket *sock)
 	if (sock->type == SOCK_RAW)
 		nfc_sock_unlink(&raw_sk_list, sk);
 
+	if (sk->sk_state == TCP_ESTABLISHED) {
+		/* Prevent rawsock_tx_work from starting new transmits and
+		 * wait for any in-progress work to finish.  This must happen
+		 * before the socket is orphaned to avoid a race where
+		 * rawsock_tx_work runs after the NCI device has been freed.
+		 */
+		sk->sk_shutdown |= SEND_SHUTDOWN;
+		cancel_work_sync(&nfc_rawsock(sk)->tx_work);
+		rawsock_write_queue_purge(sk);
+	}
+
 	sock_orphan(sk);
 	sock_put(sk);
 
-- 
2.53.0