This is a note to let you know that I've just added the patch titled drivers: net: slip: fix NPD bug in sl_tx_timeout() to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drivers-net-slip-fix-npd-bug-in-sl_tx_timeout.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 17326f41483ae21fdbdafe96568b7340a53417ac Author: Duoming Zhou <duoming@xxxxxxxxxx> Date: Tue Apr 5 21:22:06 2022 +0800 drivers: net: slip: fix NPD bug in sl_tx_timeout() [ Upstream commit ec4eb8a86ade4d22633e1da2a7d85a846b7d1798 ] When a slip driver is detaching, the slip_close() will act to cleanup necessary resources and sl->tty is set to NULL in slip_close(). Meanwhile, the packet we transmit is blocked, sl_tx_timeout() will be called. Although slip_close() and sl_tx_timeout() use sl->lock to synchronize, we don`t judge whether sl->tty equals to NULL in sl_tx_timeout() and the null pointer dereference bug will happen. (Thread 1) | (Thread 2) | slip_close() | spin_lock_bh(&sl->lock) | ... ... | sl->tty = NULL //(1) sl_tx_timeout() | spin_unlock_bh(&sl->lock) spin_lock(&sl->lock); | ... | ... tty_chars_in_buffer(sl->tty)| if (tty->ops->..) //(2) | ... | synchronize_rcu() We set NULL to sl->tty in position (1) and dereference sl->tty in position (2). This patch adds check in sl_tx_timeout(). If sl->tty equals to NULL, sl_tx_timeout() will goto out. Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx> Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx> Link: https://lore.kernel.org/r/20220405132206.55291-1-duoming@xxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c index d7882b548b79..dd95d6181afa 100644 --- a/drivers/net/slip/slip.c +++ b/drivers/net/slip/slip.c @@ -471,7 +471,7 @@ static void sl_tx_timeout(struct net_device *dev) spin_lock(&sl->lock); if (netif_queue_stopped(dev)) { - if (!netif_running(dev)) + if (!netif_running(dev) || !sl->tty) goto out; /* May be we must check transmitter timeout here ?