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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: e31d5a0594 ("caif: tty's are kref objects so take a reference")
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20260306034006.3395740-1-shuangpeng.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Shuangpeng Bai 2026-03-05 22:40:06 -05:00 committed by Jakub Kicinski
parent 87d1268521
commit 288598d80a
1 changed files with 3 additions and 0 deletions
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3
drivers/net/caif/caif_serial.c
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@ -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);