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

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Message-ID: <1410152829.11872.84.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 07 Sep 2014 22:07:09 -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 21:59 -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...



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