tty: n_gsm: fix missing explicit ldisc flush

commit 17eac652028501df7ea296b1d9b9c134db262b7d upstream.

In gsm_cleanup_mux() the muxer is closed down and all queues are removed.
However, removing the queues is done without explicit control of the
underlying buffers. Flush those before freeing up our queues to ensure
that all outgoing queues are cleared consistently. Otherwise, a new mux
connection establishment attempt may time out while the underlying tty is
still busy sending out the remaining data from the previous connection.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220414094225.4527-10-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 1b5e4bd9768ed075c4abae6944062d40e937b708..de320dc24ad5b2f9f7b9c47af2fc580449cf5463 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2101,6 +2101,7 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm)
                        gsm_dlci_release(gsm->dlci[i]);
        mutex_unlock(&gsm->mutex);
        /* Now wipe the queues */
+       tty_ldisc_flush(gsm->tty);
        list_for_each_entry_safe(txq, ntxq, &gsm->tx_list, list)
                kfree(txq);
        INIT_LIST_HEAD(&gsm->tx_list);