On 20/09/2016 06:37, Sargun Dhillon wrote: > On Thu, Sep 15, 2016 at 09:41:33PM +0200, Mickaël Salaün wrote: >> >> On 15/09/2016 06:48, Alexei Starovoitov wrote: >>> On Wed, Sep 14, 2016 at 09:38:16PM -0700, Andy Lutomirski wrote: >>>> On Wed, Sep 14, 2016 at 9:31 PM, Alexei Starovoitov >>>> wrote: >>>>> On Wed, Sep 14, 2016 at 09:08:57PM -0700, Andy Lutomirski wrote: >>>>>> On Wed, Sep 14, 2016 at 9:00 PM, Alexei Starovoitov >>>>>> wrote: >>>>>>> On Wed, Sep 14, 2016 at 07:27:08PM -0700, Andy Lutomirski wrote: >>>>>>>>>>> >>>>>>>>>>> This RFC handle both cgroup and seccomp approaches in a similar way. I >>>>>>>>>>> don't see why building on top of cgroup v2 is a problem. Is there >>>>>>>>>>> security issues with delegation? >>>>>>>>>> >>>>>>>>>> What I mean is: cgroup v2 delegation has a functionality problem. >>>>>>>>>> Tejun says [1]: >>>>>>>>>> >>>>>>>>>> We haven't had to face this decision because cgroup has never properly >>>>>>>>>> supported delegating to applications and the in-use setups where this >>>>>>>>>> happens are custom configurations where there is no boundary between >>>>>>>>>> system and applications and adhoc trial-and-error is good enough a way >>>>>>>>>> to find a working solution. That wiggle room goes away once we >>>>>>>>>> officially open this up to individual applications. >>>>>>>>>> >>>>>>>>>> Unless and until that changes, I think that landlock should stay away >>>>>>>>>> from cgroups. Others could reasonably disagree with me. >>>>>>>>> >>>>>>>>> Ours and Sargun's use cases for cgroup+lsm+bpf is not for security >>>>>>>>> and not for sandboxing. So the above doesn't matter in such contexts. >>>>>>>>> lsm hooks + cgroups provide convenient scope and existing entry points. >>>>>>>>> Please see checmate examples how it's used. >>>>>>>>> >>>>>>>> >>>>>>>> To be clear: I'm not arguing at all that there shouldn't be >>>>>>>> bpf+lsm+cgroup integration. I'm arguing that the unprivileged >>>>>>>> landlock interface shouldn't expose any cgroup integration, at least >>>>>>>> until the cgroup situation settles down a lot. >>>>>>> >>>>>>> ahh. yes. we're perfectly in agreement here. >>>>>>> I'm suggesting that the next RFC shouldn't include unpriv >>>>>>> and seccomp at all. Once bpf+lsm+cgroup is merged, we can >>>>>>> argue about unpriv with cgroups and even unpriv as a whole, >>>>>>> since it's not a given. Seccomp integration is also questionable. >>>>>>> I'd rather not have seccomp as a gate keeper for this lsm. >>>>>>> lsm and seccomp are orthogonal hook points. Syscalls and lsm hooks >>>>>>> don't have one to one relationship, so mixing them up is only >>>>>>> asking for trouble further down the road. >>>>>>> If we really need to carry some information from seccomp to lsm+bpf, >>>>>>> it's easier to add eBPF support to seccomp and let bpf side deal >>>>>>> with passing whatever information. >>>>>>> >>>>>> >>>>>> As an argument for keeping seccomp (or an extended seccomp) as the >>>>>> interface for an unprivileged bpf+lsm: seccomp already checks off most >>>>>> of the boxes for safely letting unprivileged programs sandbox >>>>>> themselves. >>>>> >>>>> you mean the attach part of seccomp syscall that deals with no_new_priv? >>>>> sure, that's reusable. >>>>> >>>>>> Furthermore, to the extent that there are use cases for >>>>>> unprivileged bpf+lsm that *aren't* expressible within the seccomp >>>>>> hierarchy, I suspect that syscall filters have exactly the same >>>>>> problem and that we should fix seccomp to cover it. >>>>> >>>>> not sure what you mean by 'seccomp hierarchy'. The normal process >>>>> hierarchy ? >>>> >>>> Kind of. I mean the filter layers that are inherited across fork(), >>>> the TSYNC mechanism, etc. >>>> >>>>> imo the main deficiency of secccomp is inability to look into arguments. >>>>> One can argue that it's a blessing, since composite args >>>>> are not yet copied into the kernel memory. >>>>> But in a lot of cases the seccomp arguments are FDs pointing >>>>> to kernel objects and if programs could examine those objects >>>>> the sandboxing scope would be more precise. >>>>> lsm+bpf solves that part and I'd still argue that it's >>>>> orthogonal to seccomp's pass/reject flow. >>>>> I mean if seccomp says 'ok' the syscall should continue executing >>>>> as normal and whatever LSM hooks were triggered by it may have >>>>> their own lsm+bpf verdicts. >>>> >>>> I agree with all of this... >>>> >>>>> Furthermore in the process hierarchy different children >>>>> should be able to set their own lsm+bpf filters that are not >>>>> related to parallel seccomp+bpf hierarchy of programs. >>>>> seccomp syscall can be an interface to attach programs >>>>> to lsm hooks, but nothing more than that. >>>> >>>> I'm not sure what you mean. I mean that, logically, I think we should >>>> be able to do: >>>> >>>> seccomp(attach a syscall filter); >>>> fork(); >>>> child does seccomp(attach some lsm filters); >>>> >>>> I think that they *should* be related to the seccomp+bpf hierarchy of >>>> programs in that they are entries in the same logical list of filter >>>> layers installed. Some of those layers can be syscall filters and >>>> some of the layers can be lsm filters. If we subsequently add a way >>>> to attach a removable seccomp filter or a way to attach a seccomp >>>> filter that logs failures to some fd watched by an outside monitor, I >>>> think that should work for lsm, too, with more or less the same >>>> interface. >>>> >>>> If we need a way for a sandbox manager to opt different children into >>>> different subsets of fancy filters, then I think that syscall filters >>>> and lsm filters should use the same mechanism. >>>> >>>> I think we might be on the same page here and just saying it different ways. >>> >>> Sounds like it :) >>> All of the above makes sense to me. >>> The 'orthogonal' part is that the user should be able to use >>> this seccomp-managed hierarchy without actually enabling >>> TIF_SECCOMP for the task and syscalls should still go through >>> fast path and all the way till lsm hooks as normal. >>> I don't want to pay _any_ performance penalty for this feature >>> for lsm hooks (and all syscalls) that don't have bpf programs attached. >> >> Yes, it seems that we are all on the same page here, and that match this >> RFC implementation. So, using the seccomp(2) *interface* to attach >> Landlock programs to a process hierarchy is still on track. :) >> > > So, I'm catching up on this after a little while away. I really like the > simplicity of the approach Daniel took with his patches. I began to have > difficulty reading your patchset once you got into using seccomp + unprivileged > mode. I would love to see a separate patchset that only have the verifier, and > lsm hook changes. Do you think you could decompose your patchset into an MVP? > OK, I'll try to split the common parts from the seccomp part, but there is already a dedicated patch for the LSM hooks [06/22].