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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, Jia-Ju Bai <baijiaju1990@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.4 016/230] isdn: i4l: isdn_tty: Fix some concurrency double-free bugs
Date:   Fri, 22 Mar 2019 12:12:34 +0100
Message-Id: <20190322111237.873712294@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 2ff33d6637393fe9348357285931811b76e1402f ]

The functions isdn_tty_tiocmset() and isdn_tty_set_termios() may be
concurrently executed.

isdn_tty_tiocmset
  isdn_tty_modem_hup
    line 719: kfree(info->dtmf_state);
    line 721: kfree(info->silence_state);
    line 723: kfree(info->adpcms);
    line 725: kfree(info->adpcmr);

isdn_tty_set_termios
  isdn_tty_modem_hup
    line 719: kfree(info->dtmf_state);
    line 721: kfree(info->silence_state);
    line 723: kfree(info->adpcms);
    line 725: kfree(info->adpcmr);

Thus, some concurrency double-free bugs may occur.

These possible bugs are found by a static tool written by myself and
my manual code review.

To fix these possible bugs, the mutex lock "modem_info_mutex" used in
isdn_tty_tiocmset() is added in isdn_tty_set_termios().

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/isdn/i4l/isdn_tty.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/isdn/i4l/isdn_tty.c b/drivers/isdn/i4l/isdn_tty.c
index 2175225af7421..8291e9cc949ad 100644
--- a/drivers/isdn/i4l/isdn_tty.c
+++ b/drivers/isdn/i4l/isdn_tty.c
@@ -1459,15 +1459,19 @@ isdn_tty_set_termios(struct tty_struct *tty, struct ktermios *old_termios)
 {
 	modem_info *info = (modem_info *) tty->driver_data;
 
+	mutex_lock(&modem_info_mutex);
 	if (!old_termios)
 		isdn_tty_change_speed(info);
 	else {
 		if (tty->termios.c_cflag == old_termios->c_cflag &&
 		    tty->termios.c_ispeed == old_termios->c_ispeed &&
-		    tty->termios.c_ospeed == old_termios->c_ospeed)
+		    tty->termios.c_ospeed == old_termios->c_ospeed) {
+			mutex_unlock(&modem_info_mutex);
 			return;
+		}
 		isdn_tty_change_speed(info);
 	}
+	mutex_unlock(&modem_info_mutex);
 }
 
 /*
-- 
2.19.1