7:13 a.m.
On Mon, Oct 21, 2019 at 08:31:37PM -0400, Paul Moore wrote:
On Mon, Oct 21, 2019 at 7:58 PM Richard Guy Briggs
<rgb(a)redhat.com> wrote:
> On 2019-10-21 17:43, Paul Moore wrote:
> > On Mon, Oct 21, 2019 at 5:38 PM Richard Guy Briggs <rgb(a)redhat.com>
wrote:
> > > On 2019-10-21 15:53, Paul Moore wrote:
> > > > On Fri, Oct 18, 2019 at 9:39 PM Richard Guy Briggs
<rgb(a)redhat.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.
I agree that one api is probably the best approach here, but I actually
think that the netlink interface is the more flexible approach. Its a
little more work for userspace (you have to marshal your data into a
netlink message before sending it, and wait for an async response), but
thats a well known pattern, and it provides significantly more
flexibility for the kernel. LSM already has a hook to audit netlink
messages in sock_sendmsg, so thats not a problem, and if you use
netlink, you get the advantage of being able to broadcast messages
within your network namespaces, facilitating any needed orchestrator
co-ordination. To do the same thing with a filesystem api, you need to
use the fanotify api, which IIRC doesn't work on proc.
Neil
> > > 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