On July 8, 2019 8:12:56 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > On 2019-05-30 19:26, Paul Moore wrote: >> On Thu, May 30, 2019 at 5:29 PM Tycho Andersen <tycho@xxxxxxxx> wrote: >>> On Thu, May 30, 2019 at 03:29:32PM -0400, Paul Moore wrote: >>>> >>>> >>>> [REMINDER: It is an "*audit* container ID" and not a general >>>> "container ID" ;) Smiley aside, I'm not kidding about that part.] >>> >>> This sort of seems like a distinction without a difference; presumably >>> audit is going to want to differentiate between everything that people >>> in userspace call a container. So you'll have to support all this >>> insanity anyway, even if it's "not a container ID". >> >> That's not quite right. Audit doesn't care about what a container is, >> or is not, it also doesn't care if the "audit container ID" actually >> matches the ID used by the container engine in userspace and I think >> that is a very important line to draw. Audit is simply given a value >> which it calls the "audit container ID", it ensures that the value is >> inherited appropriately (e.g. children inherit their parent's audit >> container ID), and it uses the value in audit records to provide some >> additional context for log analysis. The distinction isn't limited to >> the value itself, but also to how it is used; it is an "audit >> container ID" and not a "container ID" because this value is >> exclusively for use by the audit subsystem. We are very intentionally >> not adding a generic container ID to the kernel. If the kernel does >> ever grow a general purpose container ID we will be one of the first >> ones in line to make use of it, but we are not going to be the ones to >> generically add containers to the kernel. Enough people already hate >> audit ;) >> >>>> I'm not interested in supporting/merging something that isn't useful; >>>> if this doesn't work for your use case then we need to figure out what >>>> would work. It sounds like nested containers are much more common in >>>> the lxc world, can you elaborate a bit more on this? >>>> >>>> >>>> As far as the possible solutions you mention above, I'm not sure I >>>> like the per-userns audit container IDs, I'd much rather just emit the >>>> necessary tracking information via the audit record stream and let the >>>> log analysis tools figure it out. However, the bigger question is how >>>> to limit (re)setting the audit container ID when you are in a non-init >>>> userns. For reasons already mentioned, using capable() is a non >>>> starter for everything but the initial userns, and using ns_capable() >>>> is equally poor as it essentially allows any userns the ability to >>>> munge it's audit container ID (obviously not good). It appears we >>>> need a different method for controlling access to the audit container >>>> ID. >>> >>> One option would be to make it a string, and have it be append only. >>> That should be safe with no checks. >>> >>> I know there was a long thread about what type to make this thing. I >>> think you could accomplish the append-only-ness with a u64 if you had >>> some rule about only allowing setting lower order bits than those that >>> are already set. With 4 bits for simplicity: >>> >>> 1100 # initial container id >>> 1100 -> 1011 # not allowed >>> 1100 -> 1101 # allowed, but now 1101 is set in stone since there are >>> # no lower order bits left >>> >>> There are probably fancier ways to do it if you actually understand >>> math :) >> >> ;) >> >>> Since userns nesting is limited to 32 levels (right now, IIRC), and >>> you have 64 bits, this might be reasonable. You could just teach >>> container engines to use the first say N bits for themselves, with a 1 >>> bit for the barrier at the end. >> >> I like the creativity, but I worry that at some point these >> limitations are going to be raised (limits have a funny way of doing >> that over time) and we will be in trouble. I say "trouble" because I >> want to be able to quickly do an audit container ID comparison and >> we're going to pay a penalty for these larger values (we'll need this >> when we add multiple auditd support and the requisite record routing). >> >> Thinking about this makes me also realize we probably need to think a >> bit longer about audit container ID conflicts between orchestrators. >> Right now we just take the value that is given to us by the >> orchestrator, but if we want to allow multiple container orchestrators >> to work without some form of cooperation in userspace (I think we have >> to assume the orchestrators will not talk to each other) we likely >> need to have some way to block reuse of an audit container ID. We >> would either need to prevent the orchestrator from explicitly setting >> an audit container ID to a currently in use value, or instead generate >> the audit container ID in the kernel upon an event triggered by the >> orchestrator (e.g. a write to a /proc file). I suspect we should >> start looking at the idr code, I think we will need to make use of it. > > To address this, I'd suggest that it is enforced to only allow the > setting of descendants and to maintain a master list of audit container > identifiers (with a hash table if necessary later) that includes the > container owner. > > This also allows the orchestrator/engine to inject processes into > existing containers by checking that the audit container identifier is > only used again by the same owner. > > I have working code for both. Just a quick note that due to some holiday travel I'm not going to be able to adequately respond to your latest messages on this thread for at least another week, likely a bit more. I'm only checking mail to put out fires, and the audit container ID work tends to be something that starts them ;) -- paul moore www.paul-moore.com
