linux-kernel - Re: NULL pointer dereference in selinux_ip_postroute

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Date:	Wed, 08 Aug 2012 21:29:40 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Stultz <johnstul@...ibm.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Paul Moore <paul@...l-moore.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 12:14 -0700, John Stultz wrote:
> On 08/07/2012 03:37 PM, John Stultz wrote:
> > On 08/07/2012 03:17 PM, Serge E. Hallyn wrote:
> >> Quoting Paul Moore (paul@...l-moore.com):
> >>> On Tue, Aug 7, 2012 at 5:58 PM, John Stultz <john.stultz@...aro.org> 
> >>> wrote:
> >>>> On 08/07/2012 02:50 PM, Paul Moore wrote:
> >>>>> On Tue, Aug 7, 2012 at 2:12 PM, John Stultz <john.stultz@...aro.org>
> >>>>> wrote:
> >>>>>> Hi,
> >>>>>>       With my kvm environment using 3.6-rc1+, I'm seeing NULL 
> >>>>>> pointer
> >>>>>> dereferences in selinux_ip_postroute_compat(). It looks like the 
> >>>>>> sksec
> >>>>>> value
> >>>>>> is null and we die in the following line:
> >>>>>>
> >>>>>>       if (selinux_xfrm_postroute_last(sksec->sid, skb, &ad, proto))
> >>>>>>
> >>>>>> This triggers every time I shutdown the machine, but has also 
> >>>>>> triggered
> >>>>>> randomly after a few hours.
> [snip]
> >> The problem seems to be that selinux_nf_ip_init() was called, which
> >> registers the selinux_ipv4_ops (and ipv6).  Those should not get 
> >> registered
> >> if selinux ends up not being loaded (as in, if apparmor is loaded 
> >> first),
> >> since as you've found here the selinux lsm hooks won't be called to set
> >> call selinux_sk_alloc_security().
> > This sounds about right:
> > root@...tvm:~# dmesg | grep SELinux
> > [    0.004578] SELinux:  Initializing.
> > [    0.005704] SELinux:  Starting in permissive mode
> > [    2.235034] SELinux:  Registering netfilter hooks
> >
> >> I assume what's happening is that 
> >> CONFIG_SECURITY_SELINUX_BOOTPARAM_VALUE was
> >> set to 1, but selinux ended up being set to disabled after the
> >> __initcall(selinux_nf_ip_init) ran?  Weird.
> > This looks right as well:
> >
> > # zcat config.gz | grep SELINUX
> > CONFIG_SECURITY_SELINUX=y
> > CONFIG_SECURITY_SELINUX_BOOTPARAM=y
> > CONFIG_SECURITY_SELINUX_BOOTPARAM_VALUE=1
> > CONFIG_SECURITY_SELINUX_DISABLE=y
> > CONFIG_SECURITY_SELINUX_DEVELOP=y
> > CONFIG_SECURITY_SELINUX_AVC_STATS=y
> > CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE=1
> > # CONFIG_SECURITY_SELINUX_POLICYDB_VERSION_MAX is not set
> > CONFIG_DEFAULT_SECURITY_SELINUX=y
> >
> >
> > Since the problem isn't completely obvious, I'm starting a bisection 
> > to narrow this down some more.
> 
> 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 for doing this.

So sk_security is NULL and selinux crashes on it.

I guess I need to call security_sk_alloc().



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