netdev - Re: [PATCH net] ipv6: refresh rt6i_genid in ip6_pol

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Message-Id: <20140907.212742.893555292268057160.davem@davemloft.net>
Date:	Sun, 07 Sep 2014 21:27:42 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	nicolas.dichtel@...nd.com, therbert@...gle.com,
	alexander.h.duyck@...el.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: refresh rt6i_genid in ip6_pol_route()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sun, 07 Sep 2014 21:18:25 -0700

> On Sun, 2014-09-07 at 15:54 -0700, David Miller wrote:
> 
>> This might be broken.
>> 
>> We are dealing here with persistent entries in the ipv6 routine trie.
>> 
>> If you just bump the genid on the next person to look it up, other
>> sockets and cached entities might not have validated the route yet,
>> and now will falsely see the route as valid.  We have to ensure that
>> they too drop this route and perform a relookup.
> 
> I am confused, I thought it was the role of the cookie.
> 
> (Ie socket has to store its own cookie to be able to validate a route)
> 
> Before 6f3118b571b8 patch, how was this done anyway ?
> 
> If persistent routes cannot refresh the genid, then they are useless ?

I just speak about the genid aspect.

I understand that cookie (via node->fn_sernum) invalidates the path
in the fib_trie, but the genid protects against other circumstances
(matching IPSEC rule, f.e.)

You have to make sure all other sockets did a full route lookup
(including IPSEC) before you can safely adjust the genid.

I could be wrong, recheck my analysis please :-)
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