netdev - [PATCH net v2] ax25: fix use-after-free bugs caused by ax25_ds_del

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Message-Id: <20240329015023.9223-1-duoming@zju.edu.cn>
Date: Fri, 29 Mar 2024 09:50:23 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	linux-hams@...r.kernel.org,
	pabeni@...hat.com,
	kuba@...nel.org,
	edumazet@...gle.com,
	davem@...emloft.net,
	jreuter@...na.de,
	horms@...nel.org,
	Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH net v2] ax25: fix use-after-free bugs caused by ax25_ds_del_timer

When the ax25 device is detaching, the ax25_dev_device_down()
calls ax25_ds_del_timer() to cleanup the slave_timer. When
the timer handler is running, the ax25_ds_del_timer() that
calls del_timer() in it will return directly. As a result,
the use-after-free bugs could happen, one of the scenarios
is shown below:

      (Thread 1)          |      (Thread 2)
                          | ax25_ds_timeout()
ax25_dev_device_down()    |
  ax25_ds_del_timer()     |
    del_timer()           |
  ax25_dev_put() //FREE   |
                          |  ax25_dev-> //USE

In order to mitigate bugs, when the device is detaching, use
timer_shutdown_sync() to stop the timer.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
Changes in v2:
  - Call timer_shutdown_sync() in ax25_dev_device_down().

 net/ax25/ax25_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index c5462486dbc..282ec581c07 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -105,7 +105,7 @@ void ax25_dev_device_down(struct net_device *dev)
 	spin_lock_bh(&ax25_dev_lock);
 
 #ifdef CONFIG_AX25_DAMA_SLAVE
-	ax25_ds_del_timer(ax25_dev);
+	timer_shutdown_sync(&ax25_dev->dama.slave_timer);
 #endif
 
 	/*
-- 
2.17.1