linux-kernel - Re: [PATCH v3 0/4] Introduce security_create_user

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Date:   Mon, 1 Aug 2022 11:19:35 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Frederick Lawler <fred@...udflare.com>, kpsingh@...nel.org
Cc:     Martin KaFai Lau <kafai@...com>, revest@...omium.org,
        jackmanb@...omium.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        shuah@...nel.org, brauner@...nel.org, casey@...aufler-ca.com,
        ebiederm@...ssion.com, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, kernel-team@...udflare.com,
        cgzones@...glemail.com, karl@...badwolfsecurity.com
Subject: Re: [PATCH v3 0/4] Introduce security_create_user_ns()

On Mon, Aug 1, 2022 at 9:13 AM Frederick Lawler <fred@...udflare.com> wrote:
> On 7/22/22 7:20 AM, Paul Moore wrote:
> > On July 22, 2022 2:12:03 AM Martin KaFai Lau <kafai@...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.  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
(patches {2,3}/4).  For the record, I think the SELinux portion of
this patchset (path 4/4) is fine.

There is the issue of Eric's NACK, but I believe the responses that
followed his comment sufficiently addressed those concerns and it has
now been a week with no further comment from Eric; we should continue
to move forward with this.

-- 
paul-moore.com