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Date: Sun, 24 Jan 2016 01:11:03 +0100
From: Florian Westphal <fw@strlen.de>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Florian Westphal <fw@strlen.de>, Dmitry Vyukov <dvyukov@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>, Thomas Graf <tgraf@suug.ch>,
        Ken-ichirou MATSUZAWA <chamaken@gmail.com>,
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        David Herrmann <dh.herrmann@gmail.com>,
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        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>, netfilter-devel@vger.kernel.org
Subject: Re: net: GPF in netlink_getsockbyportid
Message-ID: <20160124001103.GA2748@breakpoint.cc>
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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 ].