Re: [PATCH v3 0/4] Introduce security_create_user_ns()

Paul Moore
2022-08-03T01:49:28Z

On Tue, Aug 2, 2022 at 5:25 PM KP Singh <kpsingh@kernel.org> wrote:
> On Mon, Aug 1, 2022 at 5:19 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Mon, Aug 1, 2022 at 9:13 AM Frederick Lawler <fred@cloudflare.com> wrote:
> > > On 7/22/22 7:20 AM, Paul Moore wrote:
> > > > On July 22, 2022 2:12:03 AM Martin KaFai Lau <kafai@fb.com> wrote:
> > > >
> > > >> On Thu, Jul 21, 2022 at 12:28:04PM -0500, Frederick Lawler wrote:
> > > >>> While creating a LSM BPF MAC policy to block user namespace creation, we
> > > >>> used the LSM cred_prepare hook because that is the closest hook to prevent
> > > >>> a call to create_user_ns().
> > > >>>
> > > >>> The calls look something like this:
> > > >>>
> > > >>> cred = prepare_creds()
> > > >>> security_prepare_creds()
> > > >>> call_int_hook(cred_prepare, ...
> > > >>> if (cred)
> > > >>> create_user_ns(cred)
> > > >>>
> > > >>> We noticed that error codes were not propagated from this hook and
> > > >>> introduced a patch [1] to propagate those errors.
> > > >>>
> > > >>> The discussion notes that security_prepare_creds()
> > > >>> is not appropriate for MAC policies, and instead the hook is
> > > >>> meant for LSM authors to prepare credentials for mutation. [2]
> > > >>>
> > > >>> Ultimately, we concluded that a better course of action is to introduce
> > > >>> a new security hook for LSM authors. [3]
> > > >>>
> > > >>> This patch set first introduces a new security_create_user_ns() function
> > > >>> and userns_create LSM hook, then marks the hook as sleepable in BPF.
> > > >> Patch 1 and 4 still need review from the lsm/security side.
> > > >
> > > > This patchset is in my review queue and assuming everything checks out, I expect to merge it after the upcoming merge window closes.
> > > >
> > > > I would also need an ACK from the BPF LSM folks, but they're CC'd on this patchset.
> > >
> > > Based on last weeks comments, should I go ahead and put up v4 for
> > > 5.20-rc1 when that drops, or do I need to wait for more feedback?
> >
> > In general it rarely hurts to make another revision, and I think
> > you've gotten some decent feedback on this draft, especially around
> > the BPF LSM tests; I think rebasing on Linus tree after the upcoming
> > io_uring changes are merged would be a good idea.

As I was typing up my reply I realized I mistakenly mentioned the
io_uring changes that Linus just merged today - oops! If you haven't
figured it out already, you can disregard that comment, that's a
completely different problem and a completely different set of patches
:)

> > Although as a
> > reminder to the BPF LSM folks - I'm looking at you KP Singh :) - I
> > need an ACK from you guys before I merge the BPF related patches
>
> Apologies, I was on vacation. I am looking at the patches now.
> Reviews and acks coming soon :)

No worries, we've still got the two weeks of the merge window before I
can do anything into linux-next - thanks KP!

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