FAILED: patch "[PATCH] ax25: fix use-after-free bugs caused by ax25_ds_del_timer" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-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 <stable@vger.kernel.org>.

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-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x fd819ad3ecf6f3c232a06b27423ce9ed8c20da89
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024040512-graves-stipend-babf@gregkh' --subject-prefix 'PATCH 4.19.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 <duoming@zju.edu.cn>
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.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240329015023.9223-1-duoming@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index c5462486dbca..282ec581c072 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
 
 	/*