On Wed, Jul 15, 2015 at 2:48 PM, Serge E. Hallyn <serge@xxxxxxxxxx> wrote: > On Wed, Jul 15, 2015 at 02:46:04PM -0500, Seth Forshee wrote: >> Capability sets attached to files must be ignored except in the >> user namespaces where the mounter is privileged, i.e. s_user_ns >> and its descendants. Otherwise a vector exists for gaining >> privileges in namespaces where a user is not already privileged. >> >> Add a new helper function, in_user_ns(), to test whether a user >> namespace is the same as or a descendant of another namespace. >> Use this helper to determine whether a file's capability set >> should be applied to the caps constructed during exec. >> >> Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> > > Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx> > > I think it's an ok behavior, though let's just go over the > alternatives. > > It might actually be ok to simply require that the user_ns be > equal. If I unshare a new userns in which a different uid is > mapped to root, I may not want file capabilities to be granted > to tasks in that ns. (On the other hand, I might be creating > a new user_ns specifically to not have a uid 0 mapped into it > at all, and only have file capabilities grant privilege) > > Conversely, if I unshare one user_ns with a MS_SHARED mnt_ns, mount > an ext4fs, and then (from the parent shell) unshare another user_ns > with the same mapping, intending it to be a "peer" to the first one > I'd unshared and be able to use the ext4fs it mounted. This won't > work here. That's probably best - the appropriate thing to do was > to attach to the existing user_ns. But it could end up being > limiting in some special cases, so I'm bringing it up here. > > Again I think what you have here is the simplest and most sensible > choice, so ack. > I think I'm missing something. Why is this separate from mount_may_suid? I can see why it would make sense to check s_user_ns (or maybe s_user_ns *and* the vfsmount namespace) in mount_may_suid, but I don't see why we need separate checks. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
