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

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Date:	Tue, 09 Sep 2014 14:58:39 +0200
From:	Hannes Frederic Sowa <hannes@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, 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 So, 2014-09-07 at 22:07 -0700, Eric Dumazet wrote:
> On Sun, 2014-09-07 at 21:59 -0700, David Miller wrote:
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > Date: Sun, 07 Sep 2014 21:43:54 -0700
> > 
> > > 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.
> > 
> > I'm willing to revert the change in question if you think that's the
> > sanest way forward.
> > 
> > The bug fix for more obscure use cases (IPSEC) if pointless if it
> > breaks more common things (TCP input route caching).
> 
> Lets wait for Nicolas and/or Hannes input, they might have some ideas...

My first idea was to remove rt_genid check in ip6_dst_check completely
and rt_genid_bump_ipv6() should walk the trie to increase fib6_sernum in
rt6i_nodes. I'll try this.



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