If permitted is zero (ie., no file capabilities) then I don't think this will yield any privilege for such an exec. Perhaps I missed something prior to being included in the thread, but I was under the impression that this was a case where it was intended that capabilities would be inherited..?
If you force pE' too, then this looks more like a mini-root inheritance which gets me closer to disliking this: you need to consider that we dangerously close to returning to situations like the one discussed here: https://sites.google.com/site/fullycapable/Home/thesendmailcapabilitiesissue Cheers Andrew On Wed, Feb 4, 2015 at 8:34 AM, Andy Lutomirski <l...@amacapital.net> wrote: > On Wed, Feb 4, 2015 at 8:12 AM, Andrew G. Morgan <mor...@kernel.org> wrote: >> I was thinking more like this: >> >> int override = secure(SECURE_AMBIENT_PRIVS) && >> cap_isclear(caps->inheritable.cap); >> >> CAP_FOR_EACH_U32(i) { >> __u32 permitted = caps->permitted.cap[i]; >> __u32 inheritable = override ? new->cap_bset.cap[i] : >> caps->inheritable.cap[i]; >> [...] > > To elaborate on my objection: > > For better or for worse, as a practical matter, if you drop a cap from > pP but keep it in pI, there's no way to get that cap back on the > average system to get that cap back using execve because nothing will > have that bit set in fI. I am not at all confident that changing this > is safe at this point, since there's lots of legacy code out there. > > So, how about: > > __u32 inheritable = override ? (new->cap_bset.cap[i] & permitted) : > caps->inheritable.cap[i]; > > instead? > > This still doesn't address the effective set adequately, I think. I > suspect that we'll want to always start with pE' == pP' in the new > mode, or perhaps pE' = (pP' & pE). This latter part is also a bit > dangerous and furthers my desire to restrict this to no_new_privs. > > --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/