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

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Date:	Thu, 14 Apr 2016 08:31:27 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Joe Stringer' <joe@....org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
CC:	"fw@...len.de" <fw@...len.de>,
	"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()

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).
So don't really want to orphan skb before queuing them, instead transfer
the entire resource count to the head skb when they are merged.

Although I can't imagine why IPv6 reassembly is happening on skb
associated with a socket.

	David