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. -- 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
