netdev - Re: net: GPF in netlink

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Message-ID: <20160124001103.GA2748@breakpoint.cc>
Date:	Sun, 24 Jan 2016 01:11:03 +0100
From:	Florian Westphal <fw@...len.de>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Florian Westphal <fw@...len.de>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	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

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 ].