netdev - Re: [PATCH nf] netfilter: ipv6: Orphan skbs in nf_ct_frag6

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Message-ID: <CAPWQB7EV-boR1_yaBeY8tQtHgc09+14jQ_q7yk=bpwrtqL+20Q@mail.gmail.com>
Date:	Thu, 14 Apr 2016 17:35:39 -0700
From:	Joe Stringer <joe@....org>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	Florian Westphal <fw@...len.de>,
	David Laight <David.Laight@...lab.com>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"diproiettod@...are.com" <diproiettod@...are.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH nf] netfilter: ipv6: Orphan skbs in nf_ct_frag6_gather()

On 14 April 2016 at 03:35, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Thu, Apr 14, 2016 at 10:40:15AM +0200, Florian Westphal wrote:
>> David Laight <David.Laight@...LAB.COM> wrote:
>> > From: Joe Stringer
>> > > Sent: 13 April 2016 19:10
>> > > This is the IPv6 equivalent of commit 8282f27449bf ("inet: frag: Always
>> > > orphan skbs inside ip_defrag()").
>> > >
>> > > Prior to commit 029f7f3b8701 ("netfilter: ipv6: nf_defrag: avoid/free
>> > > clone operations"), ipv6 fragments sent to nf_ct_frag6_gather() would be
>> > > cloned (implicitly orphaning) prior to queueing for reassembly. As such,
>> > > when the IPv6 message is eventually reassembled, the skb->sk for all
>> > > fragments would be NULL. After that commit was introduced, rather than
>> > > cloning, the original skbs were queued directly without orphaning. The
>> > > end result is that all frags except for the first and last may have a
>> > > socket attached.
>> >
>> > I'd have thought that the queued fragments would still want to be
>> > resource-counted against the socket (I think that is what skb->sk is for).
>>
>> No, ipv4/ipv6 reasm has its own accouting.
>>
>> > Although I can't imagine why IPv6 reassembly is happening on skb
>> > associated with a socket.
>>
>> Right, thats a much more interesting question -- both ipv4 and
>> ipv6 orphan skbs before NF_HOOK prerouting trip.
>>
>> (That being said, I don't mind the patch, I'm just be curious how this
>>  can happen).
>
> If this change is specific to get this working in ovs and its
> conntrack support, then I don't think this belong to core
> infrastructure. This should be fixed in ovs instead.

I admit I've only been able to reproduce it with OVS. My main reason
for proposing the fix this way was just because this is what the IPv4
code does, so I figured IPv6 should be consistent with that.