netdev - [PATCH 2/2] vti6: do not check for ignore

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Message-Id: <20180830125817.4567-2-cascardo@canonical.com>
Date:   Thu, 30 Aug 2018 09:58:17 -0300
From:   Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
To:     netdev@...r.kernel.org
Cc:     yoshfuji@...ux-ipv6.org, kuznet@....inr.ac.ru, davem@...emloft.net,
        herbert@...dor.apana.org.au, steffen.klassert@...unet.com,
        eyal.birger@...il.com
Subject: [PATCH 2/2] vti6: do not check for ignore_df in order to update pmtu

Before commit d6990976af7c5d8f55903bfb4289b6fb030bf754 ("vti6: fix PMTU caching
and reporting on xmit"), skb was scrubbed before checking for ignore_df. The
scrubbing meant ignore_df was false, making the check irrelevant. Now that the
scrubbing happens after that, some packets might fail the checking and dst
will not have its pmtu updated.

Not only that, but too big skb will be potentially passed down to
__xfrm6_output, causing it to fail to transmit but not free the skb, causing a
leak of skb, and consequentially a leak of dst references.

After running pmtu.sh, that shows as failure to unregister devices in a namespace:

[  311.397671] unregister_netdevice: waiting for veth_b to become free. Usage count = 1

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
---
 net/ipv6/ip6_vti.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index c72ae3a4fe09..fbd3752ea587 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -481,7 +481,7 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 	}

 	mtu = dst_mtu(dst);
-	if (!skb->ignore_df && skb->len > mtu) {
+	if (skb->len > mtu) {
 		skb_dst_update_pmtu(skb, mtu);

 		if (skb->protocol == htons(ETH_P_IPV6)) {
-- 
2.17.1