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

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Date:	Mon, 08 Sep 2014 03:28:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	nicolas.dichtel@...nd.com
Cc:	David Miller <davem@...emloft.net>, 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 Mon, 2014-09-08 at 10:11 +0200, Nicolas Dichtel wrote:
> Le 08/09/2014 07:07, Eric Dumazet a écrit :
> > 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...
> 
> The initial problem was in SCTP. Here is the thread after the v1 patch:
> http://patchwork.ozlabs.org/patch/182235/
> 
> Before the patch, SCTP stored the IPv6 route in its cache and if an IPsec
> rules was inserted after that operation, SCTP never invalidated the cached
> route to use a new xfrm route.

This thread mentions output route.

The problem I currently have with IPv6 early demux is for input routes.



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