On Thu, Jul 13, 2017 at 11:59:55AM -0400, Stephen Smalley wrote: > On Thu, 2017-07-13 at 11:48 -0400, Stephen Smalley wrote: > > On Thu, 2017-07-13 at 09:25 -0400, Paul Moore wrote: > > > On Thu, Jul 13, 2017 at 8:44 AM, Stephen Smalley <s...@tycho.nsa.gov > > > > > > > wrote: > > > > On Wed, 2017-07-12 at 20:27 -0400, Chris PeBenito wrote: > > > > > On 07/12/2017 05:38 PM, Paul Moore wrote: > > > > > > On Wed, Jul 12, 2017 at 9:26 AM, Stephen Smalley <sds@tycho.n > > > > > > sa > > > > > > .gov > > > > > > > wrote: > > > > > > > On Tue, 2017-07-11 at 17:00 -0400, Paul Moore wrote: > > > > > > > > On Mon, Jul 10, 2017 at 4:25 PM, Stephen Smalley <sds@tyc > > > > > > > > ho > > > > > > > > .nsa > > > > > > > > .gov> > > > > > > > > wrote: > > > > > > > > > > > > While I think splitting the NNP/nosuid transition > > > > > > restrictions > > > > > > might > > > > > > be a good idea under the new policy capability, I'm not sure > > > > > > it > > > > > > is > > > > > > worth the cost of a "process2" object class. > > > > > > > > > > > > With that in mind, let's do two things with this patch: > > > > > > > > > > > > * Mention the nosuid restrictions in the patch > > > > > > description. It > > > > > > doesn't need much text, but something would be good so we > > > > > > have > > > > > > documentation in the git log. > > > > > > > > > > > > * Let's pick a new permission name that is not specific to > > > > > > NNP > > > > > > or > > > > > > nosuid. IMHO, nnpnosuid_transition is ... less than good. > > > > > > Unfortunately, I'm not sure I'm much better at picking names; > > > > > > how > > > > > > about "protected_transition"? "restricted_transition"? > > > > > > "enable_transition"? "override_transition"? > > > > > > > > > > I vote for nnp_transition anyway. "No New Privileges" > > > > > encompasses > > > > > nosuid in my mind. If the two perms had been separated I would > > > > > have > > > > > been inclined to allow both every time one of them was needed, > > > > > to > > > > > make > > > > > sure no one was surprised by the behavior difference. > > > > > > > > I agree; I'll keep it as nnp_transition and just document it in > > > > the > > > > patch description. > > > > > > Sorry to be a stubborn about this, but nnp_transition makes little > > > sense for the nosuid restriction. Like it or not, NNP has a > > > concrete > > > meaning which is distinct from nosuid mounts. We don't have to > > > pick > > > any of the permission names I tossed out, none of those were very > > > good, but I would like to see something that takes both NNP and > > > nosuid > > > into account, or preferably something that doesn't use either name > > > explicitly but still conveys the meaning. > > > > NNP is essentially a superset of nosuid; it applies to all execve() > > calls by the process and its descendants rather than only to execve() > > calls on specially marked filesystems. So I viewed it as the more > > general term. > > > > If that's not viable, I can't think of anything clearer or better > > than > > nnp_nosuid_transition. That clearly links it to what it means (allow > > a > > SELinux domain transition under NNP or nosuid). It is somewhat ugly > > and verbose but it is clear in what it means, which I think is more > > important. All of your suggestions IMHO were less clear since they > > had > > no clear linkage to either NNP or nosuid, and I couldn't tell from > > reading the permission name what it meant. The SELinux domain > > transition isn't protected, it isn't restricted, it isn't clear what > > enable_transition means versus the regular transition or > > dyntransition > > permissions, and we aren't overriding a transition but rather > > allowing > > one under NNP/nosuid. > > > > The only other alternative I see is to introduce a process2 class and > > use separate nnp_transition and nosuid_transition permissions (but in > > practice I expect them to be both allowed or denied together). Note > > that this will require two avtab and AVC entries for every domain > > pair > > (if we allow whichever one ends up going in the process2 class), so > > that has an impact on policy and AVC size. Don't really see that as > > worthwhile. > > > > Other approach would be to make the nosuid transition checks file- > > based > > instead so that it would go in the file class (while the nnp one > > would > > remain in the process class), but I don't think that's really what we > > want either. Difference between "Can domain D1 transition under > > nosuid > > to D2?" and "Can domain D1 transition under nosuid when executing > > file > > with type T1?". > > Just to be clear, we would also be separately checking regular > transition permission between the old and new contexts on these > transitions, so you would need both: > allow D1 D2:process transition; > allow D1 T1:file nosuid_transition; > if we took the latter approach. > > So we wouldn't lose entirely on a domain-to-domain check, but it would > no longer be domain-to-domain for the nosuid part. > > Whereas with original approach, we end up requiring: > allow D1 D2:process transition; > allow D1 D2:process nnp_nosuid_transition; # or whatever permission name is > used
I don't know if i understand all the ins-and-outs of the matter but i think i do like the idea of differentiating between nosuid_transition and nnp_transition It provides more flexibility because i might not want to allow one or the other automatically. I do not think it its a good idea to allow a process to transiton on nosuid mounted filesystems just because i am forced to allow it nnp. So since the stuff is ugly one way or another might as well make it consistent with SELinux flexibility goals Just my preference but I dont have a really strong opinion on the matter > > > > > On a separate note, I plan to cc luto on the next version of the > > patch > > as I suspect he will have concerns about relaxing this constraint on > > NNP and this likely requires updating > > Documentation/prctl/no_new_privs* > > and the man pages that describe NNP behavior. > > > > The other model would be to figure out a way to make the typebounds > > logic work cleanly in a manner that preserves the desired NNP/nosuid > > invariant _and_ doesn't require leaking unnecessary accesses into the > > ancestor domains that make them less secure, plus CIL support for > > automatically propagating permissions in the desired way. But I > > haven't yet come up with a way to do that. We can do it in some > > cases > > by creating typebounds between the object types, e.g.: > > typebounds parent_t child_t; > > allow child_t self:process execmem; > > allow child_t child_exec_t:file entrypoint; > > allow child_t child_tmp_t:file create; > > can be allowed via: > > allow parent_t child_t:process execmem; # an otherwise nonsensical > > rule > > typebounds parent_exec_t child_exec_t; > > typebounds parent_tmp_t child_tmp_t; > > but this breaks down when there isn't an equivalent type and > > permission > > set already allowed to the parent for every type allowed to the > > child. -- Key fingerprint = 5F4D 3CDB D3F8 3652 FBD8 02D5 3B6C 5F1D 2C7B 6B02 https://sks-keyservers.net/pks/lookup?op=get&search=0x3B6C5F1D2C7B6B02 Dominick Grift
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