From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Jaeyoung Chung <jjy600901@snu.ac.kr>,
	Eulgyu Kim <eulgyukim@snu.ac.kr>,
	Qingfang Deng <qingfang.deng@linux.dev>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 1333/1376] slip: remove slip_hangup() to fix use-after-free in slip_receive_buf()
Date: Sat, 12 Sep 2026 09:02:39 +0200
Message-ID: <20260912065637.241505932@linuxfoundation.org>
In-Reply-To: <20260912065607.535295758@linuxfoundation.org>
References: <20260912065607.535295758@linuxfoundation.org>
User-Agent: quilt/0.69
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

6.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 23c53269f2baaedf2d92784290cb9ef6db2a3bce ]

Jaeyoung Chung and Eulgyu Kim reported a slab-use-after-free read
in slip_receive_buf() when racing against tty hangup.

tty_ldisc_hangup() calls ld->ops->hangup() while holding only
a read lock on tty->ldisc_sem (via tty_ldisc_ref()).
Because slip_hangup() simply called slip_close(), it ran concurrently
with reader functions such as slip_receive_buf().

slip_close() unregisters and frees the net device and its private
struct slip, causing concurrent reader threads in slip_receive_buf()
to dereference freed memory.

Line discipline close() is already guaranteed to be called under
the write lock of tty->ldisc_sem during hangup processing
(in tty_ldisc_reinit() or tty_ldisc_kill()).

Remove slip_hangup() so teardown is serialized cleanly by slip_close().

Fixes: 5342b77c4123 ("slip: Clean up create and destroy")
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Reported-by: Eulgyu Kim <eulgyukim@snu.ac.kr>
Closes: https://lore.kernel.org/netdev/20260825150655.1450271-1-jjy600901@snu.ac.kr/
Cc: Qingfang Deng <qingfang.deng@linux.dev>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260826105238.3323436-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/slip/slip.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index 117de9eb5e09e..bc155dddae8b1 100644
--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c
@@ -886,8 +886,6 @@ static int slip_open(struct tty_struct *tty)
  * Close down a SLIP channel.
  * This means flushing out any pending queues, and then returning. This
  * call is serialized against other ldisc functions.
- *
- * We also use this method fo a hangup event
  */
 
 static void slip_close(struct tty_struct *tty)
@@ -915,11 +913,6 @@ static void slip_close(struct tty_struct *tty)
 	unregister_netdev(sl->dev);
 	/* sl_uninit() has dropped the slip_devs[] entry by now */
 }
-
-static void slip_hangup(struct tty_struct *tty)
-{
-	slip_close(tty);
-}
  /************************************************************************
   *			STANDARD SLIP ENCAPSULATION		  	 *
   ************************************************************************/
@@ -1280,7 +1273,6 @@ static struct tty_ldisc_ops sl_ldisc = {
 	.name 		= "slip",
 	.open 		= slip_open,
 	.close	 	= slip_close,
-	.hangup	 	= slip_hangup,
 	.ioctl		= slip_ioctl,
 	.receive_buf	= slip_receive_buf,
 	.write_wakeup	= slip_write_wakeup,
-- 
2.53.0