[PATCH AUTOSEL 4.19 12/12] drivers: net: slip: fix NPD bug in sl_tx_timeout()

Sasha Levin
2022-04-12T01:08:27Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ 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@zju.edu.cn>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20220405132206.55291-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/slip/slip.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index 5d864f812955..3ec8d16a4633 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 ?
--
2.35.1