From 27d53323664c549b5bb2dfaaf6f7ad6e0376a64e Mon Sep 17 00:00:00 2001 From: Xin Long Date: Tue, 7 Jul 2020 02:02:32 +0800 Subject: [PATCH] l2tp: remove skb_dst_set() from l2tp_xmit_skb() 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 Signed-off-by: Xin Long Acked-by: James Chapman Tested-by: James Chapman Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 6d7ef78c88af..6434d17e6e8e 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, /* Queue the packet to IP for output */ skb->ignore_df = 1; + skb_dst_drop(skb); #if IS_ENABLED(CONFIG_IPV6) if (l2tp_sk_is_v6(tunnel->sock)) error = inet6_csk_xmit(tunnel->sock, skb, NULL); @@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len goto out_unlock; } - /* Get routing info from the tunnel socket */ - skb_dst_drop(skb); - skb_dst_set(skb, sk_dst_check(sk, 0)); - inet = inet_sk(sk); fl = &inet->cork.fl; switch (tunnel->encap) { -- 2.39.5