[SRU][J][PATCH 1/1] ax25: fix use-after-free bugs caused by ax25_ds_del_timer

[Massimiliano Pellizzer]

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

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 at zju.edu.cn>
Reviewed-by: Simon Horman <horms at kernel.org>
Link: https://lore.kernel.org/r/20240329015023.9223-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit fd819ad3ecf6f3c232a06b27423ce9ed8c20da89)
CVE-2024-35887
Signed-off-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com>
---
 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 4842f63821c8..fe730fad1c38 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -103,7 +103,7 @@ 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
 
 	/*
-- 
2.43.0