netdev - [RFC PATCH net 0/4] ip6: datagram: Update dst cache of a connected datagram sk during pmtu update

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Date:	Fri, 1 Apr 2016 15:56:27 -0700
From:	Martin KaFai Lau <kafai@...com>
To:	netdev <netdev@...r.kernel.org>
CC:	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Wei Wang <weiwan@...gle.com>, Kernel Team <kernel-team@...com>
Subject: [RFC PATCH net 0/4] ip6: datagram: Update dst cache of a connected datagram sk during pmtu update

There is a case in connected UDP socket such that
getsockopt(IPV6_MTU) will return a stale MTU value. The reproducible
sequence could be the following:
1. Create a connected UDP socket
2. Send some datagrams out
3. Receive a ICMPV6_PKT_TOOBIG
4. No new outgoing datagrams to trigger the sk_dst_check()
   logic to update the sk->sk_dst_cache.
5. getsockopt(IPV6_MTU) returns the mtu from the invalid
   sk->sk_dst_cache instead of the newly created RTF_CACHE clone.

Patch 1 and 2 are the prep work.
Patch 3 and 4 are the fixes.