Re: [AppArmor 39/45] AppArmor: Profile loading and manipulation,pathname matching

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On Sat, 9 Jun 2007, Sean wrote:


On Sat, 9 Jun 2007 00:04:15 -0700 (PDT)
[email protected] 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 thing.
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 kernel.
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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