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. --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
