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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,
        syzbot <syzbot+cf155def4e717db68a12@syzkaller.appspotmail.com>,
        stable <stable@kernel.org>, Jiri Slaby <jirislaby@kernel.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Fedor Pchelkin <pchelkin@ispras.ru>
Subject: [PATCH 5.10 03/79] tty: n_gsm: initialize more members at gsm_alloc_mux()
Date:   Tue, 13 Sep 2022 16:04:08 +0200
Message-Id: <20220913140350.450170649@linuxfoundation.org>
In-Reply-To: <20220913140350.291927556@linuxfoundation.org>
References: <20220913140350.291927556@linuxfoundation.org>
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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit 4bb1a53be85fcb1e24c14860e326a00cdd362c28 upstream.

syzbot is reporting use of uninitialized spinlock at gsmld_write() [1], for
commit 32dd59f ("tty: n_gsm: fix race condition in gsmld_write()")
allows accessing gsm->tx_lock before gsm_activate_mux() initializes it.

Since object initialization should be done right after allocation in order
to avoid accessing uninitialized memory, move initialization of
timer/work/waitqueue/spinlock from gsmld_open()/gsm_activate_mux() to
gsm_alloc_mux().

Link: https://syzkaller.appspot.com/bug?extid=cf155def4e717db68a12 [1]
Fixes: 32dd59f ("tty: n_gsm: fix race condition in gsmld_write()")
Reported-by: syzbot <syzbot+cf155def4e717db68a12@syzkaller.appspotmail.com>
Tested-by: syzbot <syzbot+cf155def4e717db68a12@syzkaller.appspotmail.com>
Cc: stable <stable@kernel.org>
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/2110618e-57f0-c1ce-b2ad-b6cacef3f60e@I-love.SAKURA.ne.jp
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/n_gsm.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2200,11 +2200,6 @@ static int gsm_activate_mux(struct gsm_m
 {
 	struct gsm_dlci *dlci;
 
-	timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
-	init_waitqueue_head(&gsm->event);
-	spin_lock_init(&gsm->control_lock);
-	spin_lock_init(&gsm->tx_lock);
-
 	if (gsm->encoding == 0)
 		gsm->receive = gsm0_receive;
 	else
@@ -2306,6 +2301,10 @@ static struct gsm_mux *gsm_alloc_mux(voi
 	mutex_init(&gsm->mutex);
 	kref_init(&gsm->ref);
 	INIT_LIST_HEAD(&gsm->tx_list);
+	timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
+	init_waitqueue_head(&gsm->event);
+	spin_lock_init(&gsm->control_lock);
+	spin_lock_init(&gsm->tx_lock);
 
 	gsm->t1 = T1;
 	gsm->t2 = T2;