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    SubjectRe: [AppArmor 39/45] AppArmor: Profile loading and manipulation,pathname matching
    On Sat, 9 Jun 2007, Sean wrote:

    > On Sat, 9 Jun 2007 00:04:15 -0700 (PDT)
    > wrote:
    >> if it was this easy just have SELinux set the label == path
    >> you first need to figure out what the path is. right now this can't be
    >> done, the AA paches provide this capability.
    > The question is: why not just extend SELinux to include AA functionality
    > rather than doing a whole new subsystem. What exactly about AA demands
    > an entire new infrastructure rather than just building on what already
    > exists in the kernel?
    >> second, the AA policies aren't based just on the path, they are based on
    >> the program accessing the path, then the path. you can have two different
    >> policies for two different programs accessing the same path, but for most
    >> programs (although, not nessasarily most activity) there will be no
    >> policy, and therefor no need to check the path.
    > It seems the main purported advantage of AA is it doesn't require maintaining
    > labels on files etc. In fact, that's the only conceptual difference I can
    > see other than a simpler policy file format. So why not just make an AA
    > extension to SELinux that implements this main difference (ie. create labels
    > on the fly).

    becouse the SELinux people don't want to have this in their code for one

    you seem to be ignoring the SELinux people who say that pathnames are
    fundamentally different from labels, labels stay with the data if the file
    is renamed, path names do not. multiple hard-links to the same file will
    always have the same label for SELinux, but could have very different
    permissions with AA

    labels are part of policy, policy is not supposed to be decided by the

    SELinux treats all files with the same label the same. to have the same
    ability to treat every file differntly that AA has SELinux would have to
    give every file a different label.

    > Then have a userspace program that converts the pretty-peace-and-love
    > AA policy file format into the baby-killing SELinux format and feed it
    > into the kernel.
    > All of a sudden you've implemented the main features of AA with very
    > few changes to the kernel. It should be more maintainable, and much
    > easier to get accepted into the kernel.

    how will you know how many labels you need to put into your policy that
    you load into the kernel?

    how will the kernel figure out what label to use for a file

    and the userspace code that converts the policy needs to know the names
    when it feeds the policy into the kernel.

    and you still need to implement the new LSM hooks that AA is asking for to
    figure out what the path to a file is.

    >> but even if you did these things, why would it be an advantage to use a
    >> mechanism to create a dummy label and pass it off to different code rather
    >> then just decideing at that point?
    > Because it requires you to reimplement much of what is already in the kernel.
    > It requires you to be able to understand an entire new policy mechanism
    > instead of just piggybacking on what already exists.

    the policy mechanism is supposed to be the LSM hooks, and AA is trying to
    re-use them.

    >> once the AA code knows what the policy
    >> for this path is for this program (which it would need to know to set the
    > Again you're only looking at the way the AA code is _today_. If it were
    > refactored to be an extension of SELinux, there would be no reason for the
    > AA kernel code to know any policy whatsoever. All it would need to know
    > is a path-to-label mapping. SELinux would then enforce the AA policy
    > that it received from your userspace tool that translates your native
    > AA policy format into SELinux-lingo.

    after you change SELinux to be able to do everything that AA does then you
    can tell SELinux to act like AA, true but irrelavent.

    >> label) how is it a win to pass this off to another chunk of code? you
    > It's a win because the policy enforcement code is already in the kernel.
    > All you have to do is extend SELinux to create labels on the fly and provide
    > a userspace tool to convert the nice AA policy files into something SELinux
    > can use.
    >> would also need to make sure that the SELinux code didn't try to cache the
    >> label for future use either, becouse in the future the access may be from
    >> another program and so the policy that's needed is different.
    > You seem to be quibbling over small little unimportant details and refusing
    > to part with your current implementation. It would seem the easiest way to
    > get the functionality you want into the kernel is to be a bit more flexible
    > on implementation.

    first off, and for the record, it's not _my_ implementation. I have
    nothing to do with writing AA.

    I am just someone who manages hundreds of servers for which AA would be a
    good fit. In the past I've gone to a lot of effort to get less security
    then AA would provide to implement seperate services in seperate chroot
    sandboxes. I'm looking for easier and better options, I've looked at
    SELinux and don't believe that I can produce a reasonable policy in a
    reasonable amount of time (and I don't trust distro vendors to do it for
    me, they have to allow a lot of things that don't make sense on my
    systems, and I occasionally need to allow something that wouldn't make
    sense in the general case, let alone all the software I run that the disto
    doesn't know anything about)

    chroot sandboxes, virtual machines, containers all have the problem that
    when you need to have more then one application interacting they need to
    be put togeather and the basic mechanism doesn't provide you any security
    against each other.

    SELinux is aiming for 'perfect' security, I'll readily admit that, just
    like I'll admit that AA is only aiming for 'good enough' security, but
    that 'good enough' security would help me and I don't see any way to get
    to SELinux's 'perfect' security.

    I also don't care about the details of how it gets implemented, but when
    the AA people have a working implementation, and the SELinux people are
    strongly opposed to the concept, I don't see any advantage in trying to
    get the AA people to throw away a lot of their working code to try and get
    people (many of who have be very insulting frankly) to accept such
    fandamental changes.

    if the SELinux people had responded to the announcement of AA with "that's
    a nice idea, if we add these snippits from your code to SELinux then we
    can do the same thing" it would be a very different story.

    but as always patches talk louder then anything else, if you believe that
    the efforts should be combined so strongly why don't you start submitting
    the appropriate patches to SELinux to make it able to do what AA does?

    David Lang
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