FAILED: patch "[PATCH] ax25: fix use-after-free bugs caused by ax25_ds_del_timer" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x fd819ad3ecf6f3c232a06b27423ce9ed8c20da89
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024040506-earmark-skydiver-ab1c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fd819ad3ecf6f3c232a06b27423ce9ed8c20da89 Mon Sep 17 00:00:00 2001
From: Duoming Zhou <[email protected]>
Date: Fri, 29 Mar 2024 09:50:23 +0800
Subject: [PATCH] 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.

index c5462486dbca..282ec581c072 100644
@@ -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
 
 	/*