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SubjectRe: [PATCH BUGFIX -rc3] Smack: Don't register smackfs if we're not loaded
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Hi Linus,

[Adding SELinux devs to CC list, please follow to the SELinux point.]

On Tue, Mar 04, 2008 at 09:21:19AM -0800, Linus Torvalds wrote:
>
>
> On Tue, 4 Mar 2008, Ahmed S. Darwish wrote:
> >
> > Smackfs initialization without an enabled Smack leads to
> > an early Oops that renders the system unusable.
>
> I really think this is bogus. Global enables like this are just wrong, and
> a sign that something else bad is going on.
>
> What is the oops? Why does it happen?
>

The problem occurs when Smack is built-in the kernel but not chosen
to register itself on boot. Smack was not chosen on boot cause either
security=AnotherLSM or security=NonExistentLSM.

In all cases, init_smk_fs() ,which registers smackfs, got called
cause it's an __initcall(init_smack_fs).
This include the cases where smack __was not__ chosen on boot.

Making smackfs mountable when Smack is not registered leads to:

1- an Oops by dereferncing the NULL security pointer: current->security (*)

2- Smackfs code got executed though naturally all the code assumes
that smack is already registered with the security system leading
to several problems.

3- The bogus idea of having a subsystem interface available when the
subsystem itself is not available!

So the global is used in init_smk_fs to not register smackfs if
Smack wasn't enabled on boot.

---- SELinux:
I think the SELinux folks faced the same problem too. In my first
local iteration of the security= parameter patch, I forgot to set
`selinux_disable = 1' if SELinux wasn't chosen on boot.

This led to dozen of SELinux Udev events and also led to selinuxfs
being available even though SELinux hooks _weren't_ registered.

Regards,

(*)
Could not save the oops cause it occured too early, but
it was like this:

__init_call
init_smk_fs(void)
smk_unlbl_ambient(NULL)
/*
* Here: current->security = NULL, cause SMACK initial setup
* was not executed.
*/
smack_to_secid(current->security)
strncmp(.., current->security, ..)
--

"Better to light a candle, than curse the darkness"

Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com



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