tty: n_gsm: fix missing explicit ldisc flush

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 6b953dfbb15573d906ace08d248ac65a5e22f923..1430d7f83bd2ed9e8839e95fbf68079e7f84ec50 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2152,6 +2152,7 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
                        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);