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Date: Mon, 25 Jan 2016 18:03:41 +0800
From: Herbert Xu <herbert@gondor.apana.org.au>
To: Florian Westphal <fw@strlen.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>, Dmitry Vyukov <dvyukov@google.com>,
        "David S. Miller" <davem@davemloft.net>, Thomas Graf <tgraf@suug.ch>,
        Ken-ichirou MATSUZAWA <chamaken@gmail.com>,
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        David Herrmann <dh.herrmann@gmail.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        netdev <netdev@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>, netfilter-devel@vger.kernel.org,
        Pablo Neira Ayuso <pablo@netfilter.org>
Subject: Re: net: GPF in netlink_getsockbyportid
Message-ID: <20160125100341.GA6735@gondor.apana.org.au>
References: <CACT4Y+Zmwr0VbfB5RAoLTCJJAF7epZWbbMkHxtXUwvF3tXbrgQ@mail.gmail.com>
 <20160123192502.GB17729@breakpoint.cc>
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 <20160124001103.GA2748@breakpoint.cc>
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On Sun, Jan 24, 2016 at 01:11:03AM +0100, Florian Westphal wrote:
> Daniel Borkmann <daniel@iogearbox.net> wrote:
> > On 01/23/2016 08:25 PM, Florian Westphal wrote:
> > >Dmitry Vyukov <dvyukov@google.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@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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