linux-kernel - Re: NULL pointer dereference in selinux_ip_postroute

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Date:	Wed, 08 Aug 2012 21:38:21 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Paul Moore <paul@...l-moore.com>
Cc:	John Stultz <johnstul@...ibm.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	lkml <linux-kernel@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	selinux@...ho.nsa.gov, Eric Dumazet <edumazet@...gle.com>,
	john.johansen@...onical.com
Subject: Re: NULL pointer dereference in selinux_ip_postroute_compat

On Wed, 2012-08-08 at 15:26 -0400, Paul Moore wrote:
> On Wednesday, August 08, 2012 12:14:42 PM John Stultz wrote:
> > So I bisected this down and it seems to be the following commit:
> > 
> > commit be9f4a44e7d41cee50ddb5f038fc2391cbbb4046
> > Author: Eric Dumazet <edumazet@...gle.com>
> > Date:   Thu Jul 19 07:34:03 2012 +0000
> > 
> >      ipv4: tcp: remove per net tcp_sock
> > 
> > 
> > It doesn't revert totally cleanly, but after fixing up the rejections
> > and booting with this patch removed on top of Linus' head the oops on
> > shutdown goes away.
> 
> Thanks!
> 
> It looks the like there is a bug in ip_send_unicast_reply() which uses a 
> inet_sock/sock struct which does not have the LSM data properly initialized. 
> 
> I'll put together a patch shortly.
> 

Something like this ?

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ba39a52..027a331 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1524,6 +1524,10 @@ void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,
 	sk->sk_priority = skb->priority;
 	sk->sk_protocol = ip_hdr(skb)->protocol;
 	sk->sk_bound_dev_if = arg->bound_dev_if;
+#ifdef CONFIG_SECURITY
+	if (!sk->sk_security && security_sk_alloc(sk, PF_INET, GFP_ATOMIC))
+			goto out;
+#endif
 	sock_net_set(sk, net);
 	__skb_queue_head_init(&sk->sk_write_queue);
 	sk->sk_sndbuf = sysctl_wmem_default;
@@ -1539,7 +1543,7 @@ void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,
 		skb_set_queue_mapping(nskb, skb_get_queue_mapping(skb));
 		ip_push_pending_frames(sk, &fl4);
 	}
-
+out:
 	put_cpu_var(unicast_sock);
 
 	ip_rt_put(rt);


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