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

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Date:	Sun, 07 Sep 2014 21:43:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
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()

On Sun, 2014-09-07 at 21:27 -0700, David Miller wrote:
> 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 :-)

So this whole genid protection can not work, unless we make sure a
socket cannot share a route with another socket.

This means we have to clone all routes.



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