Subject: Re: net: GPF in netlink_getsockbyportid

From: Pablo Neira Ayuso <[email-masked]>
Date: Mon, 25 Jan 2016 11:17:20 +0100

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 <[email-masked]> wrote:
> > > On 01/23/2016 08:25 PM, Florian Westphal wrote:
> > > >Dmitry Vyukov <[email-masked]> 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/