linux-kernel - [PATCH 4/4] tty: n_gsm: Fix the test for if DLCI0 is open

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Message-ID: <20180426055421.GB15363@mwanda>
Date:   Thu, 26 Apr 2018 08:54:21 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sun Peng <sun_peng@...sec.com.cn>
Cc:     Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        security@...nel.org, Tony Lindgren <tony@...mide.com>,
        Lars Poeschel <poeschel@...onage.de>,
        Sascha Hauer <s.hauer@...gutronix.de>
Subject: [PATCH 4/4] tty: n_gsm: Fix the test for if DLCI0 is open

Logically, if gsm->dlci[0] is NULL then it's not open.  Also if it's
NULL then we would Oops when we do dlci_get(gsm->dlci[0]); at the end
of the function.

Reported-by: Sun Peng <sun_peng@...sec.com.cn>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 44e9c5e3dbc1..660153538ca7 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2919,7 +2919,7 @@ static int gsmtty_install(struct tty_driver *driver, struct tty_struct *tty)
 	perspective as we don't have to worry about this
 	if DLCI0 is lost */
 	mutex_lock(&gsm->mutex);
-	if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN) {
+	if (!gsm->dlci[0] || gsm->dlci[0]->state != DLCI_OPEN) {
 		mutex_unlock(&gsm->mutex);
 		return -EL2NSYNC;
 	}