From: Xin Long <lucien....@gmail.com>
Date: Tue, 7 Jul 2020 02:02:32 +0800
> In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
> skb's dst. However, it will eventually call inet6_csk_xmit() or
> ip_queue_xmit() where skb's dst will be overwritten by:
>
> skb_dst_set_noref(skb, dst);
>
> without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
>
> unregister_netdevice: waiting for eth0 to become free. Usage count = 1
>
> This can be reproduced by simply running:
>
> # modprobe l2tp_eth && modprobe l2tp_ip
> # sh ./tools/testing/selftests/net/l2tp.sh
>
> So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
> should be dropped. This patch is to fix it by removing skb_dst_set()
> from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
>
> Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
> Reported-by: Hangbin Liu <liuhang...@gmail.com>
> Signed-off-by: Xin Long <lucien....@gmail.com>
Applied and queued up for -stable, thank you.
