linux-kernel - Re: net: GPF in __netlink_ns

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Message-ID: <20160118092047.GA30682@gondor.apana.org.au>
Date:	Mon, 18 Jan 2016 17:20:47 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Thomas Graf <tgraf@...g.ch>,
	Daniel Borkmann <daniel@...earbox.net>,
	Ken-ichirou MATSUZAWA <chamaken@...il.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Florian Westphal <fw@...len.de>,
	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>,
	Eric Dumazet <edumazet@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: net: GPF in __netlink_ns_capable

On Sat, Jan 16, 2016 at 01:08:33AM +0100, Richard Weinberger wrote:
> On Fri, Jan 15, 2016 at 11:31 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > Call Trace:
> >  [<     inline     >] netlink_ns_capable net/netlink/af_netlink.c:1417
> >  [<ffffffff8529c0a5>] netlink_capable+0x25/0x30 net/netlink/af_netlink.c:1432
> 
> Hmm, we're crashing because NETLINK_CB(skb).sk is NULL.
> netlink_dump() creates a new skb without a netlink control block,
> but infiniband's dump functions use netlink_capable() which needs a valid
> NETLINK_CB(skb).sk.
> 
> What about something like that?

No you can't do it here as netlink_unicast also calls this and for
that case you'd be overwriting the original sending user-space
socket with the kernel socket.

I'm adding Eric Bierderman as he wrote some of the code in question.

Cheers,
-- 
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