On Tue, Aug 30, 2016 at 10:33:31PM +0200, Mickaël Salaün wrote: > > > On 30/08/2016 22:23, Andy Lutomirski wrote: > > 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. > > OK, I like that, but I think it could be done on a second time. :) I don't. Single FD that is a collection of objects seems an odd abstraction to me. I also don't see what it actually solves. I think lsm and seccomp should be orthogonal and not tied into each other. -- 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
