"Serge E. Hallyn" <se...@hallyn.com> writes: > Quoting Eric W. Biederman (ebied...@xmission.com): >> "Serge E. Hallyn" <se...@hallyn.com> writes: >> >> > Quoting Eric W. Biederman (ebied...@xmission.com): >> >> "Serge E. Hallyn" <se...@hallyn.com> writes: >> >> >> >> > Quoting Eric W. Biederman (ebied...@xmission.com): >> >> >> >> >> >> Andy Lutomirski pointed out that the current behavior of allowing the >> >> >> owner of a user namespace to have all caps when that owner is not in a >> >> >> parent user namespace is wrong. >> >> > >> >> > To make sure I understand right, the issue is when a uid is mapped >> >> > into multiple namespaces. >> >> >> >> Yes. >> >> >> >> i.e. uid 1000 in ns1 may own ns2, but uid 1000 in ns3 does not? >> >> >> >> I am not certain of your example. >> >> >> >> The simple case is: >> >> >> >> init_user_ns: >> >> child_user_ns1 (owned by uid == 0 [in all user namespaces]) >> >> child_user_ns2 (owned by uid == 0 [ in all user namespaces]) >> >> >> >> >> >> root (uid == 0) in child_user_ns2 has all rights over anything in >> >> child_user_ns1. >> > >> > Well that is only if there was no mapping. (since we're comparing >> > kuids, not uid_ts). right? If you didn't map uid 0 in child_user_ns2 >> > to another id in the parent ns, you weren't all *that* serious about >> > isolating the ns. >> > >> > The case I was thinking is >> > >> > init_user_ns: [0-uidmax] >> > child_user_ns1 [100000-199999] >> > child_user_ns2 [100000-199999] >> > child_user_ns3 [200000-299999] > > Wait is my example above possible? Or does child_user_ns3's range need > to be a subset of child_user_ns2's? > > In which case it would be > > child_user_ns1 [100000-199999] > child_user_ns2 [100000-199999] > child_user_ns3 [120000-129999] >
Yes. You have to nest uids. >> > with unfortunate mappings - ns1 and ns2 should have had nonoverlapping >> > ranges, but in any case now uid 1000 in ns1 can exert privilege over >> > ns3. Again, uids comparisons will succeed for file access anyway, so >> > ns1 can 0wn ns2 and ns3 other ways. >> >> Yes yours is the more realistic scenario. Mine was simplified to be clear. >> >> > Heck I'm starting to think the bug is a feature - surely given the >> > mappings above I meant for ns1 and ns2 to bleed privilege to each >> > other? >> >> The serious problem is that privileges can bleed up. A user in >> ns3 can wind up owning ns2 or ns1. Which totally defeats the permission >> model. You have CAP_DAC_OVERRIDE so you don't even need access to files >> you own, etc, etc. > > Would that not require intervention from the init_user_ns? In my > example above (let's add that ns2 is owned by kuid.uid=1000 in > init_user_ns), root in child_user_ns2 cannot map kuid.val=0 or > kuid.val=1000 into ns3 because 0 and 1000 are not in the range > 100000-199999. So there is no uid in child_user_ns3 which is able > to spoof uid=0 in child_user_ns1. Right. It does require having the uid of the owner of ns1 or ns2 in ns3. So you have to explicitly allow it. What I don't see is any point in allowing something like that. After taking a second look I just realized that this is completely unexploitable with the code that is currently merged. As creating a grand child user namespace is competelely impossible. Creating a user namespace is requires capable(CAP_SYS_ADMIN) which is never present in anything but the initial user namespace. That said I think the current semantics of cap_capable are completely fatal to reasoning about user namespaces. A child user namespace having capabilities against processes in it's parent seems totally bizarre and pretty dangerous from a capabilities standpoint. That said Serge I think I have lost track of the point of your question. Eric -- 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/
