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

Stephen Smalley
2008-09-18T18:34:10Z

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

> 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.

--
Stephen Smalley
National Security Agency