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SubjectRe: NULL pointer dereference in selinux_ip_postroute_compat
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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@paul-moore.com):
> >>> On Tue, Aug 7, 2012 at 5:58 PM, John Stultz <john.stultz@linaro.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@linaro.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@testvm:~# 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@google.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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