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?
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