linux-kernel - Re: net: GPF in netlink

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Date:	Mon, 25 Jan 2016 11:17:20 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Florian Westphal <fw@...len.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Graf <tgraf@...g.ch>,
	Ken-ichirou MATSUZAWA <chamaken@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	netfilter-devel@...r.kernel.org
Subject: Re: net: GPF in netlink_getsockbyportid

On Mon, Jan 25, 2016 at 06:03:41PM +0800, Herbert Xu wrote:
> On Sun, Jan 24, 2016 at 01:11:03AM +0100, Florian Westphal wrote:
> > Daniel Borkmann <daniel@...earbox.net> wrote:
> > > On 01/23/2016 08:25 PM, Florian Westphal wrote:
> > > >Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > > >
> > > >[ CC nf-devel, not sure if its nfnetlink fault or NETLINK_MMAP ]
> > > >
> > > >>The following program causes GPF in netlink_getsockbyportid:
> > [..]
> > 
> > > >CONFIG_NETLINK_MMAP and nfnetlink batching strike in unison :-/
> > > >
> > > >root cause is in nfnetlink_rcv_batch():
> > > >
> > > >296 replay:
> > > >297         status = 0;
> > > >298
> > > >299         skb = netlink_skb_clone(oskb, GFP_KERNEL);
> > > >
> > > >The clone op doesn't copy oskb->sk, so we oops in
> > > >__netlink_alloc_skb -> netlink_getsockbyportid() when nfnetlink_rcv_batch
> > > >tries to send netlink ack.
> > > 
> > > If indeed oskb is the mmap'ed netlink skb, then it's not even allowed
> > > to call into skb_clone()
> > 
> > Right, but in this case there is no mmap'd netlink sk involved -- we
> > crash when we try to look up dst netlink socket to see if there is an
> > mmap'd ring attached.
> > 
> > [ and that code isn't there with CONFIG_NETLINK_MMAP=n ].
> 
> Let's CC Pablo since he wrote the code in question.

I have just sent this patch:

http://patchwork.ozlabs.org/patch/572489/