From 7349660438603ed19282e75949561406531785a5 Mon Sep 17 00:00:00 2001
From: Daniel Starke <daniel.starke@siemens.com>
Date: Fri, 1 Jul 2022 14:23:32 +0200
Subject: [PATCH] tty: n_gsm: fix resource allocation order in gsm_activate_mux()
Git-commit: 7349660438603ed19282e75949561406531785a5
Patch-mainline: v6.0-rc1
References: git-fixes

Within gsm_activate_mux() all timers and locks are initiated before the
actual resource for the control channel is allocated. This can lead to race
conditions.

Allocate the control channel DLCI object first to avoid race conditions.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220701122332.2039-2-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/n_gsm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 79869f2b570c..ba399a660573 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2497,6 +2497,10 @@ static int gsm_activate_mux(struct gsm_mux *gsm)
 	struct gsm_dlci *dlci;
 	int ret;
 
+	dlci = gsm_dlci_alloc(gsm, 0);
+	if (dlci == NULL)
+		return -ENOMEM;
+
 	timer_setup(&gsm->kick_timer, gsm_kick_timer, 0);
 	timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
 	INIT_WORK(&gsm->tx_work, gsmld_write_task);
@@ -2513,9 +2517,6 @@ static int gsm_activate_mux(struct gsm_mux *gsm)
 	if (ret)
 		return ret;
 
-	dlci = gsm_dlci_alloc(gsm, 0);
-	if (dlci == NULL)
-		return -ENOMEM;
 	gsm->has_devices = true;
 	gsm->dead = false;		/* Tty opens are now permissible */
 	return 0;
-- 
2.35.3