Re: [RFC 3/3] ima: make the integrity inode cache per namespace

[Christian Brauner <christian.brauner@ubuntu.com>]

On Mon, Nov 29, 2021 at 11:03:17PM -0600, Serge Hallyn wrote:
> On Mon, Nov 29, 2021 at 12:04:29PM -0500, Stefan Berger wrote:
> > 
> > On 11/29/21 11:16, Christian Brauner wrote:
> > > On Mon, Nov 29, 2021 at 09:35:39AM -0600, Serge Hallyn wrote:
> > > > On Mon, Nov 29, 2021 at 09:46:55AM -0500, James Bottomley wrote:
> > > > > On Mon, 2021-11-29 at 15:22 +0100, Christian Brauner wrote:
> > > > > > On Mon, Nov 29, 2021 at 09:10:29AM -0500, James Bottomley wrote:
> > > > > > 
> > > I kept thinking about this question while I was out running and while I
> > > admittedly have reacted poorly to CLONE_NEWIMA patches before it feels
> > > to me that this is the right approach after all. Making it part of
> > > userns at least in this form isn't clean.
> > > 
> > > I think attaching a uuid to a userns alone for the sake of IMA is wrong.
> > > Additionally, I think a uuid only for the userns is too limited. This is
> > > similar to the problem of the audit container id. If we have some sort
> > > of uuid for ima it will automatically evolve into something like a
> > > container id (I'm not even arguing that this is necessarily wrong.).
> > > We also have the issue that we then have the container audit id thing -
> > > if this ever lands and the ima userns uuid. All that makes it quite
> > > messy.
> > > 
> > > I think CLONE_NEWIMA is ultimately nicer and allows the implementation
> > > to be decoupled from the userns and self-contained as possible. This
> > > also means that ima ns works for privileged containers which sure is a
> > > valid use-case.
> > 
> > The thing is that piggy backing on the user namespace at least allows us to
> > 'always see' where IMA's keyring is (across setns()). If we were using an
> > independent IMA namespace how would we guarantee that the user sees the
> > keyring for IMA appraisal? We would at least have to take a reference (as in
> > get_user_ns()) to the user namespace when the IMA namespace is created so
> > that it at least the association of IMA namespace to user namespace remains
> 
> Maybe we pull they keyring info into a new struct which is referred
> to and pinned by both user_ns and ima_ns?  (But I actually am ignorant
> of how ima is using the keyrings, so again I need to go do some reading.)

That's one way of doing it and we'd be able to shrink struct
user_namespace because of it if we have to go down that road anyway.

> 
> More moving parts isn't my first choice.  But if you need namespaced IMA
> for containers that aren't doing CLONE_NEWUSER, then a separate ima_ns is
> your only option.  Is that a requirement for you?