netdev - Re: [Bug #11500] /proc/net bug related to selinux

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Date:	Fri, 19 Sep 2008 09:58:43 -0700 (PDT)
From:	david@...g.hm
To:	Stephen Smalley <sds@...ho.nsa.gov>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Moore <paul.moore@...com>, jmorris@...ei.org, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	netdev@...r.kernel.org, Eric Paris <eparis@...isplace.org>
Subject: Re: [Bug #11500] /proc/net bug related to selinux

On Thu, 18 Sep 2008, Stephen Smalley wrote:

> On Thu, 2008-09-18 at 11:09 -0700, Eric W. Biederman wrote:
>> Stephen Smalley <sds@...ho.nsa.gov> writes:
>>
>>> On Thu, 2008-09-18 at 08:38 -0400, Stephen Smalley wrote:
>>>> I do however think that the mantra that we can't require users to update
>>>> policy for kernel changes is unsupportable in general.  The precise set
>>>> of permission checks on a given operation is not set in stone and it is
>>>> not part of the kernel/userland interface/contract.  Policy isn't
>>>> "userspace"; it governs what userspace can do, and it has to adapt to
>>>> kernel changes.
>>>
>>> I should note here that for changes to SELinux, we have gone out of our
>>> way to avoid such breakage to date through the introduction of
>>> compatibility switches, policy flags to enable any new checks, etc
>>> (albeit at a cost in complexity and ever creeping compatibility code).
>>> But changes to the rest of the kernel can just as easily alter the set
>>> of permission checks that get applied on a given operation, and I don't
>>> think we are always going to be able to guarantee that new kernel + old
>>> policy will Just Work.
>>
>> I know of at least 2 more directories that I intend to turn into
>> symlinks into somewhere under /proc/self.  How do we keep from
>> breaking selinux policies when I do that?
>
> I suspect we could tweak the logic in selinux_proc_get_sid() to always
> label all symlinks under /proc with the base proc_t type already used
> for e.g. /proc/self, at which point existing policies would be ok.

so if proc is mounted anywhere other then /proc the selinux policy would 
do odd things?

David Lang

>> For comparison how do we handle sysfs?
>
> Unresolved; presently has a single label for all nodes.
> See https://bugzilla.redhat.com/show_bug.cgi?id=228902
> for prior discussion of fine-grained labeling support for sysfs.
>
>> How do we handle device nodes in tmpfs?
>
> udev has selinux support - looks up the appropriate context in a
> userland config file (file_contexts) via libselinux matchpathcon(3) and
> sets it upon creation.  tmpfs has long supported getting/setting
> security.* attributes.
>
>> Ultimately do we want to implement xattrs and inotify on /proc?
>> Or is there another way that would simplify maintenance?
>
> If proc supported setxattr, then I suppose early userspace could label
> it instead of the kernel needing to determine a label internally.  But
> not sure how we'd cleanly migrate to avoid breakage with old userspace.
>
>
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