linux-kernel - Re: NULL pointer dereference in selinux_ip_postroute

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Date:	Wed, 8 Aug 2012 15:59:31 -0400
From:	Eric Paris <eparis@...isplace.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Paul Moore <paul@...l-moore.com>,
	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, Aug 8, 2012 at 3:38 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2012-08-08 at 15:26 -0400, Paul Moore wrote:

> 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);

Seems wrong.  We shouldn't ever need ifdef CONFIG_SECURITY in core
code.  Ifndef CONF_SECURITY then security_sk_alloc() is a static
inline return 0;   I guess the question is "Where did the sk come
from"?  Why wasn't security_sk_alloc() called when it was allocated?
Should it have been updated at some time and that wasn't done either?
Seems wrong to be putting packets on the queue for a socket where the
security data was never allocated and was never set to its proper
state.

there must be a bigger bug here...

-Eric
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