netdev - Re: net: GPF in netlink

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Date:	Mon, 25 Jan 2016 18:03:41 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Florian Westphal <fw@...len.de>
Cc:	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,
	Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: net: GPF in netlink_getsockbyportid

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.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt