> Good point about CAP_DAC_OVERRIDE on files you own. > > I think there is an argument that you are playing dangerous games with > the permission system there, as it isn't effectively a file you own if > you can't read it, and you can't change it's permissions. Append-only files are useful - particularly for logging. It could also simply be a non-readable file on a R/O filesystem. > Given little things like that I can completely see no_new_privs meaning > you can't create a user namespace. That seems consistent with the > meaning and philosophy of no_new_privs. So simple it is hard to get > wrong. Yes, I could totally buy the argument that no_new_privs should prevent creating a user ns. However, there's also setns() and that's a fair bit harder to reason about. Entirely deny it? But that actually seems potentially useful... Allow it but cap it? That's what this does... > We could do more clever things like plug this whole in user namespaces, > and that would not hurt my feelings. Sure, this particular one wouldn't be all that easy I think... and how many such holes are there? I found this particular one *after* your first reply in this thread. > However unless that is our only > choice to avoid badly breaking userspace I would have to have to depend > on user namespaces being perfect for no_new_privs to be a proper jail. This stuff is ridiculously complex to get right from userspace. :-( > As a general rule user namespaces are where we tackle the subtle scary > things that should work, and no_new_privs is where we implement a simple > hard to get wrong jail. Most of the time the effect is the same to an > outside observer (bounded permissions), but there is a real difference > in difficulty of implementation. So, where to now... Would you accept patches that: - make no_new_priv block user ns creation? - make no_new_priv block user ns transition? Or perhaps we can assume that lack of create privs is sufficient, and if there's a pre-existing user ns for you to enter, then that's acceptable... Although this implies you probably always want to combine no_new_privs with a leaf user ns, or no_new_privs isn't all that useful for root in root ns... This added complexity, probably means it should be blocked... - inherits bset across user ns creation/transition based on X? [this is the one we care about, because there are simply too many bugs in the kernel wrt. certain caps] X could be: - a new flag similar to no_new_priv - a new securebit flag (w/lockbit) [provided securebits survive a userns transition, haven't checked] - or perhaps a new capability - something else? How do we make forward progress? _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
