linux-kernel - Re: NULL pointer dereference in selinux_ip_postroute

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Date:	Wed, 08 Aug 2012 12:49:41 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Paul Moore <paul@...l-moore.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 08/08/2012 12:38 PM, Eric Dumazet wrote:
> On Wed, 2012-08-08 at 15:26 -0400, Paul Moore wrote:
>> 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);

I can't comment on the patch itself, but I tested it against Linus' HEAD 
and it seems to resolve the oops on shutdown for me.

thanks
-john

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