linux-kernel - Re: NULL pointer dereference in selinux_ip_postroute

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Date:	Thu, 09 Aug 2012 09:30:42 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Eric Paris <eparis@...isplace.org>,
	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,
	LSM <linux-security-module@...r.kernel.org>
Subject: Re: NULL pointer dereference in selinux_ip_postroute_compat

On Wednesday, August 08, 2012 05:00:26 PM Casey Schaufler wrote:
> On 8/8/2012 2:54 PM, Eric Dumazet wrote:
>
> By the way, once this proved to be an issue that involved
> more than just SELinux it needed to go onto the LSM list as
> well.

Yes, you're right.

> > On Wed, 2012-08-08 at 16:46 -0400, Paul Moore wrote:
> >> On Wednesday, August 08, 2012 10:32:52 PM Eric Dumazet wrote:
> >>> On Wed, 2012-08-08 at 22:09 +0200, Eric Dumazet wrote:
> >>> +static int smack_sk_alloc_security(struct sock *sk, int ...
> >>>  {
> >>>  	char *csp = smk_of_current();
> >>>  	struct socket_smack *ssp;
> >>> 
> >>> +	if (check && sk->sk_security)
> >>> +		return 0;
> >>> +
> >>> 
> >>>  	ssp = kzalloc(sizeof(struct socket_smack), gfp_flags);
> >>>  	if (ssp == NULL)
> >>>  	
> >>>  		return -ENOMEM;
> >> 
> >> In the case of Smack, when the kernel boolean is true I think the right
> >> solution is to use smack_net_ambient.
> 
> I confess that my understanding of unicast is limited.
> If the intention is to send an unlabeled packet then
> indeed smack_net_ambient is the way to go.

Well, the intention isn't necessarily to send an unlabeled packet, although 
that may be the end result.

In the case of a TCP reset the kernel/ambient label it is hard to argue that 
the kernel/ambient label is not the correct solution; in this case there was 
never an associated socket so the kernel itself needs to respond.

In the case of a TCP syn-recv and timewait ACK things are a little less clear.  
Eric (Dumazet), it looks like we have a socket in tcp_v4_reqsk_send_ack() and 
tcp_v4_timewait_ack(), any reason why we can't propagate the socket down to 
ip_send_unicast_reply()?

-- 
paul moore
www.paul-moore.com

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