This is a note to let you know that I've just added the patch titled ax25: NPD bug when detaching AX25 device to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ax25-npd-bug-when-detaching-ax25-device.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 1ade48d0c27d5da1ccf4b583d8c5fc8b534a3ac8 Mon Sep 17 00:00:00 2001 From: Lin Ma <linma@xxxxxxxxxx> Date: Fri, 17 Dec 2021 10:29:41 +0800 Subject: ax25: NPD bug when detaching AX25 device From: Lin Ma <linma@xxxxxxxxxx> commit 1ade48d0c27d5da1ccf4b583d8c5fc8b534a3ac8 upstream. The existing cleanup routine implementation is not well synchronized with the syscall routine. When a device is detaching, below race could occur. static int ax25_sendmsg(...) { ... lock_sock() ax25 = sk_to_ax25(sk); if (ax25->ax25_dev == NULL) // CHECK ... ax25_queue_xmit(skb, ax25->ax25_dev->dev); // USE ... } static void ax25_kill_by_device(...) { ... if (s->ax25_dev == ax25_dev) { s->ax25_dev = NULL; ... } Other syscall functions like ax25_getsockopt, ax25_getname, ax25_info_show also suffer from similar races. To fix them, this patch introduce lock_sock() into ax25_kill_by_device in order to guarantee that the nullify action in cleanup routine cannot proceed when another socket request is pending. Signed-off-by: Hanjie Wu <nagi@xxxxxxxxxx> Signed-off-by: Lin Ma <linma@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ax25/af_ax25.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -85,8 +85,10 @@ static void ax25_kill_by_device(struct n again: ax25_for_each(s, &ax25_list) { if (s->ax25_dev == ax25_dev) { - s->ax25_dev = NULL; spin_unlock_bh(&ax25_list_lock); + lock_sock(s->sk); + s->ax25_dev = NULL; + release_sock(s->sk); ax25_disconnect(s, ENETUNREACH); spin_lock_bh(&ax25_list_lock); Patches currently in stable-queue which might be from linma@xxxxxxxxxx are queue-5.10/hamradio-improve-the-incomplete-fix-to-avoid-npd.patch queue-5.10/hamradio-defer-ax25-kfree-after-unregister_netdev.patch queue-5.10/ax25-npd-bug-when-detaching-ax25-device.patch