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. :)
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