From 288598d80a068a0e9281de35bcb4ce495f189e2a Mon Sep 17 00:00:00 2001 From: Shuangpeng Bai Date: Thu, 5 Mar 2026 22:40:06 -0500 Subject: [PATCH] serial: caif: hold tty->link reference in ldisc_open and ser_release A reproducer triggers a KASAN slab-use-after-free in pty_write_room() when caif_serial's TX path calls tty_write_room(). The faulting access is on tty->link->port. Hold an extra kref on tty->link for the lifetime of the caif_serial line discipline: get it in ldisc_open() and drop it in ser_release(), and also drop it on the ldisc_open() error path. With this change applied, the reproducer no longer triggers the UAF in my testing. Link: https://gist.github.com/shuangpengbai/c898debad6bdf170a84be7e6b3d8707f Link: https://lore.kernel.org/netdev/20260301220525.1546355-1-shuangpeng.kernel@gmail.com Fixes: e31d5a05948e ("caif: tty's are kref objects so take a reference") Signed-off-by: Shuangpeng Bai Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20260306034006.3395740-1-shuangpeng.kernel@gmail.com Signed-off-by: Jakub Kicinski --- drivers/net/caif/caif_serial.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c index b90890030751..1873d8287bb9 100644 --- a/drivers/net/caif/caif_serial.c +++ b/drivers/net/caif/caif_serial.c @@ -297,6 +297,7 @@ static void ser_release(struct work_struct *work) dev_close(ser->dev); unregister_netdevice(ser->dev); debugfs_deinit(ser); + tty_kref_put(tty->link); tty_kref_put(tty); } rtnl_unlock(); @@ -331,6 +332,7 @@ static int ldisc_open(struct tty_struct *tty) ser = netdev_priv(dev); ser->tty = tty_kref_get(tty); + tty_kref_get(tty->link); ser->dev = dev; debugfs_init(ser, tty); tty->receive_room = 4096; @@ -339,6 +341,7 @@ static int ldisc_open(struct tty_struct *tty) rtnl_lock(); result = register_netdevice(dev); if (result) { + tty_kref_put(tty->link); tty_kref_put(tty); rtnl_unlock(); free_netdev(dev);