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

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Date:	Mon, 08 Sep 2014 14:16:58 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Eric Dumazet <eric.dumazet@...il.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()

Le 08/09/2014 12:28, Eric Dumazet a écrit :
> 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.
Yes, it was the target.

>
> The problem I currently have with IPv6 early demux is for input routes.
It's clearly a regression.

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