linux-kernel - Re: net: GPF in __netlink_ns

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Date:	Sat, 16 Jan 2016 01:08:33 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	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>
Subject: Re: net: GPF in __netlink_ns_capable

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?

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 81dc1bb..bb40ec5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -919,6 +919,7 @@ static void netlink_skb_set_owner_r(struct sk_buff
*skb, struct sock *sk)
 {
        WARN_ON(skb->sk != NULL);
        skb->sk = sk;
+       NETLINK_CB(skb).sk = sk;
        skb->destructor = netlink_skb_destructor;
        atomic_add(skb->truesize, &sk->sk_rmem_alloc);
        sk_mem_charge(sk, skb->truesize);
-- 
Thanks,
//richard