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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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