On Tue, Aug 30, 2016 at 1:20 PM, Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > On 30/08/2016 20:55, Andy Lutomirski wrote: >> On Sun, Aug 28, 2016 at 2:42 AM, Mickaël Salaün <mic@xxxxxxxxxxx> wrote: >>> >>> >>> On 28/08/2016 10:13, Andy Lutomirski wrote: >>>> On Aug 27, 2016 11:14 PM, "Mickaël Salaün" <mic@xxxxxxxxxxx> wrote: >>>>> >>>>> >>>>> On 27/08/2016 22:43, Alexei Starovoitov wrote: >>>>>> On Sat, Aug 27, 2016 at 09:35:14PM +0200, Mickaël Salaün wrote: >>>>>>> On 27/08/2016 20:06, Alexei Starovoitov wrote: >>>>>>>> On Sat, Aug 27, 2016 at 04:06:38PM +0200, Mickaël Salaün wrote: >>>>>>>>> As said above, Landlock will not run an eBPF programs when not strictly >>>>>>>>> needed. Attaching to a cgroup will have the same performance impact as >>>>>>>>> attaching to a process hierarchy. >>>>>>>> >>>>>>>> Having a prog per cgroup per lsm_hook is the only scalable way I >>>>>>>> could come up with. If you see another way, please propose. >>>>>>>> current->seccomp.landlock_prog is not the answer. >>>>>>> >>>>>>> Hum, I don't see the difference from a performance point of view between >>>>>>> a cgroup-based or a process hierarchy-based system. >>>>>>> >>>>>>> Maybe a better option should be to use an array of pointers with N >>>>>>> entries, one for each supported hook, instead of a unique pointer list? >>>>>> >>>>>> yes, clearly array dereference is faster than link list walk. >>>>>> Now the question is where to keep this prog_array[num_lsm_hooks] ? >>>>>> Since we cannot keep it inside task_struct, we have to allocate it. >>>>>> Every time the task is creted then. What to do on the fork? That >>>>>> will require changes all over. Then the obvious optimization would be >>>>>> to share this allocated array of prog pointers across multiple tasks... >>>>>> and little by little this new facility will look like cgroup. >>>>>> Hence the suggestion to put this array into cgroup from the start. >>>>> >>>>> I see your point :) >>>>> >>>>>> >>>>>>> Anyway, being able to attach an LSM hook program to a cgroup thanks to >>>>>>> the new BPF_PROG_ATTACH seems a good idea (while keeping the possibility >>>>>>> to use a process hierarchy). The downside will be to handle an LSM hook >>>>>>> program which is not triggered by a seccomp-filter, but this should be >>>>>>> needed anyway to handle interruptions. >>>>>> >>>>>> what do you mean 'not triggered by seccomp' ? >>>>>> You're not suggesting that this lsm has to enable seccomp to be functional? >>>>>> imo that's non starter due to overhead. >>>>> >>>>> Yes, for now, it is triggered by a new seccomp filter return value >>>>> RET_LANDLOCK, which can take a 16-bit value called cookie. This must not >>>>> be needed but could be useful to bind a seccomp filter security policy >>>>> with a Landlock one. Waiting for Kees's point of view… >>>>> >>>> >>>> I'm not Kees, but I'd be okay with that. I still think that doing >>>> this by process hierarchy a la seccomp will be easier to use and to >>>> understand (which is quite important for this kind of work) than doing >>>> it by cgroup. >>>> >>>> A feature I've wanted to add for a while is to have an fd that >>>> represents a seccomp layer, the idea being that you would set up your >>>> seccomp layer (with syscall filter, landlock hooks, etc) and then you >>>> would have a syscall to install that layer. Then an unprivileged >>>> sandbox manager could set up its layer and still be able to inject new >>>> processes into it later on, no cgroups needed. >>> >>> A nice thing I didn't highlight about Landlock is that a process can >>> prepare a layer of rules (arraymap of handles + Landlock programs) and >>> pass the file descriptors of the Landlock programs to another process. >>> This process could then apply this programs to get sandboxed. However, >>> for now, because a Landlock program is only triggered by a seccomp >>> filter (which do not follow the Landlock programs as a FD), they will be >>> useless. >>> >>> The FD referring to an arraymap of handles can also be used to update a >>> map and change the behavior of a Landlock program. A master process can >>> then add or remove restrictions to another process hierarchy on the fly. >> >> Maybe this could be extended a little bit. The fd could hold the >> seccomp filter *and* the LSM hook filters. FMODE_EXECUTE could give >> the ability to install it and FMODE_WRITE could give the ability to >> modify it. >> > > This is interesting! It should be possible to append the seccomp stack > of a source process to the seccomp stack of the target process when a > Landlock program is passed and then activated through seccomp(2). > > For the FMODE_EXECUTE/FMODE_WRITE, are you suggesting to manage > permission of the eBPF program FD in a specific way? > This wouldn't be an eBPF program FD -- it would be an FD encapsulating an entire configuration including seccomp BPF program, whatever landlock stuff is associated, and eventual seccomp monitor configuration (once I write that code), etc. You wouldn't say "attach this process's seccomp stack to me" -- you'd say "attach this seccomp layer to me". A decision that we'd have to make would be whether the FD links to the parent layer or whether it can be attached without regard to what the parent layer is. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
