linux-kernel - Re: [PATCH ghak90 V7 20/21] audit: add capcontid to set contid outside init_user

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Date:   Mon, 21 Oct 2019 20:31:37 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        sgrubb@...hat.com, omosnace@...hat.com, dhowells@...hat.com,
        simo@...hat.com, Eric Paris <eparis@...isplace.org>,
        Serge Hallyn <serge@...lyn.com>, ebiederm@...ssion.com,
        nhorman@...driver.com, Dan Walsh <dwalsh@...hat.com>,
        mpatel@...hat.com
Subject: Re: [PATCH ghak90 V7 20/21] audit: add capcontid to set contid
 outside init_user_ns

On Mon, Oct 21, 2019 at 7:58 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> On 2019-10-21 17:43, Paul Moore wrote:
> > On Mon, Oct 21, 2019 at 5:38 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> > > On 2019-10-21 15:53, Paul Moore wrote:
> > > > On Fri, Oct 18, 2019 at 9:39 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> > > > > On 2019-09-18 21:22, Richard Guy Briggs wrote:
> > > > > > Provide a mechanism similar to CAP_AUDIT_CONTROL to explicitly give a
> > > > > > process in a non-init user namespace the capability to set audit
> > > > > > container identifiers.
> > > > > >
> > > > > > Use audit netlink message types AUDIT_GET_CAPCONTID 1027 and
> > > > > > AUDIT_SET_CAPCONTID 1028.  The message format includes the data
> > > > > > structure:
> > > > > > struct audit_capcontid_status {
> > > > > >         pid_t   pid;
> > > > > >         u32     enable;
> > > > > > };
> > > > >
> > > > > Paul, can I get a review of the general idea here to see if you're ok
> > > > > with this way of effectively extending CAP_AUDIT_CONTROL for the sake of
> > > > > setting contid from beyond the init user namespace where capable() can't
> > > > > reach and ns_capable() is meaningless for these purposes?
> > > >
> > > > I think my previous comment about having both the procfs and netlink
> > > > interfaces apply here.  I don't see why we need two different APIs at
> > > > the start; explain to me why procfs isn't sufficient.  If the argument
> > > > is simply the desire to avoid mounting procfs in the container, how
> > > > many container orchestrators can function today without a valid /proc?
> > >
> > > Ok, sorry, I meant to address that question from a previous patch
> > > comment at the same time.
> > >
> > > It was raised by Eric Biederman that the proc filesystem interface for
> > > audit had its limitations and he had suggested an audit netlink
> > > interface made more sense.
> >
> > I'm sure you've got it handy, so I'm going to be lazy and ask: archive
> > pointer to Eric's comments?  Just a heads-up, I'm really *not* a fan
> > of using the netlink interface for this, so unless Eric presents a
> > super compelling reason for why we shouldn't use procfs I'm inclined
> > to stick with /proc.
>
> It was actually a video call with Eric and Steve where that was
> recommended, so I can't provide you with any first-hand communication
> about it.  I'll get more details...

Yeah, that sort of information really needs to be on the list.

> So, with that out of the way, could you please comment on the general
> idea of what was intended to be the central idea of this mechanism to be
> able to nest containers beyond the initial user namespace (knowing that
> a /proc interface is available and the audit netlink interface isn't
> necessary for it to work and the latter can be easily removed)?

I'm not entirely clear what you are asking about, are you asking why I
care about nesting container orchestrators?  Simply put, it is not
uncommon for the LXC/LXD folks to see nested container orchestrators,
so I felt it was important to support that use case.  When we
originally started this effort we probably should have done a better
job reaching out to the LXC/LXD folks, we may have caught this
earlier.  Regardless, we caught it, and it looks like we are on our
way to supporting it (that's good).

Are you asking why I prefer the procfs approach to setting/getting the
audit container ID?  For one, it makes it easier for a LSM to enforce
the audit container ID operations independent of the other audit
control APIs.  It also provides a simpler interface for container
orchestrators.  Both seem like desirable traits as far as I'm
concerned.

> > > The intent was to switch to the audit netlink interface for contid,
> > > capcontid and to add the audit netlink interface for loginuid and
> > > sessionid while deprecating the proc interface for loginuid and
> > > sessionid.  This was alluded to in the cover letter, but not very clear,
> > > I'm afraid.  I have patches to remove the contid and loginuid/sessionid
> > > interfaces in another tree which is why I had forgotten to outline that
> > > plan more explicitly in the cover letter.

-- 
paul moore
www.paul-moore.com