On Tue, Jun 13, 2017 at 10:45:02AM -0700, James Bottomley wrote: > On Tue, 2017-06-13 at 11:14 -0600, Tycho Andersen via Containers wrote: > > Hi Stefan, > > > > On Tue, Jun 13, 2017 at 11:47:26AM -0400, Stefan Berger wrote: > > > On 05/08/2017 02:11 PM, Serge E. Hallyn wrote: > > > > Root in a non-initial user ns cannot be trusted to write a > > > > traditional security.capability xattr. If it were allowed to do > > > > so, then any unprivileged user on the host could map his own uid > > > > to root in a private namespace, write the xattr, and execute the > > > > file with privilege on the host. > > > > > > > > However supporting file capabilities in a user namespace is very > > > > desirable. Not doing so means that any programs designed to run > > > > with limited privilege must continue to support other methods of > > > > gaining and dropping privilege. For instance a program installer > > > > must detect whether file capabilities can be assigned, and assign > > > > them if so but set setuid-root otherwise. The program in turn > > > > must know how to drop partial capabilities, and do so only if > > > > setuid-root. > > > > > > Hi Serge, > > > > > > > > > I have been looking at patch below primarily to learn how we > > > could apply a similar technique to security.ima and security.evm > > > for a namespaced IMA. From the paragraphs above I thought that you > > > solved the problem of a shared filesystem where one now can write > > > different security.capability xattrs by effectively supporting for > > > example security.capability[uid=1000] and > > > security.capability[uid=2000] written into the filesystem. Each > > > would then become visible as security.capability if the userns > > > mapping is set appropriately. > > > > One disadvantage of this approach is that whoever is setting up the > > container would need to go touch the security.ima attribute for each > > file in the contianer, which would slow down container creation time. > > For capabilities this makes sense, because you might want the file to > > have different capabilities in different namespaces, but for IMA, > > since the file hash will be the same in every namespace, > > Actually, this isn't necessarily true: IMA may have the hash, you're > right, but I suspect in most container use cases it will have the > signature. It's definitely a use case that the container will be using > a different keyring from the host, so different signatures are surely > possible for the same underlying image file. > > One might imagine doing the above via overlays, because the new > signature should override the old. Yes, good point, thanks. Assuming the container and the host are using the same keyring, we could design it in such a way that the container engine doesn't need to touch every file on creation, which would be very nice. Tycho _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
