Re: [PATCH ghak90 V7 20/21] audit: add capcontid to set contid outside init_user_ns

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&gt; 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&gt; 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&gt; 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