netdev - Re: [PATCH] ipv6: Fix the pmtu path for connected UDP socket

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Date:	Tue, 22 Mar 2016 16:36:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Wei Wang <tracywwnj@...il.com>, Martin KaFai Lau <kafai@...com>,
	Wei Wang <weiwan@...gle.com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv6: Fix the pmtu path for connected UDP socket

On Tue, 2016-03-22 at 13:13 -0700, Cong Wang wrote:
> On Tue, Mar 22, 2016 at 11:03 AM, Wei Wang <tracywwnj@...il.com> wrote:
> > Thanks Martin and Cong.
> >
> > I guess then we are going with the following fix in ip6_sk_update_pmtu():
> > 1. call ip6_upate_pmtu() as it is
> > 2. do a dst_check()
> > 3. re-lookup() if it is invalid
> > 4. and then do a ip6_dst_store()/dst_set
> 
> Exactly, please try the attached patch. Note I did nothing more than a
> compile test.
> 
> Does it make sense to you now?


Hard to reply on your patch as it was not inlined.

1) Lot of code duplication, for some reason I do not yet understand.

ip6_sk_update_pmtu() and ip6_update_pmtu() will basically do the same
thing...

2)

+       if (sk->sk_state == TCP_ESTABLISHED)
+               ip6_dst_store(sk, dst, &iph->daddr, &iph->saddr);
+out:


ip6_dst_store() will do :

np->daddr_cache = daddr;  (&iph->daddr)
np->saddr_cache = saddr;  (&iph->saddr)

So when skb is freed, daddr_cache & saddr_cache point to freed data.