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

[david]

On Thu, 18 Sep 2008, Stephen Smalley wrote:

> On Thu, 2008-09-18 at 11:09 -0700, Eric W. Biederman wrote:
> > Stephen Smalley <sds@xxxxxxxxxxxxx> 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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