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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH 5.15 165/177] tty: n_gsm: fix missing explicit ldisc flush
Date:   Wed,  4 May 2022 18:45:58 +0200
Message-Id: <20220504153108.285574527@linuxfoundation.org>
In-Reply-To: <20220504153053.873100034@linuxfoundation.org>
References: <20220504153053.873100034@linuxfoundation.org>
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From: Daniel Starke <daniel.starke@siemens.com>

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>
---
 drivers/tty/n_gsm.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2087,6 +2087,7 @@ static void gsm_cleanup_mux(struct gsm_m
 			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);