On Wed, Nov 19, 2014 at 03:09:11PM +0100, Serge E. Hallyn wrote: > Quoting Miklos Szeredi (miklos@xxxxxxxxxx): > > On Wed, Nov 19, 2014 at 9:50 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > On Tue, Nov 18, 2014 at 4:21 PM, Seth Forshee > > > <seth.forshee@xxxxxxxxxxxxx> wrote: > > >>> I asked around a bit, and it turns out there are use cases for nested > > >> containers (i.e. a container within a container) where the rootfs for > > >> the outer container mounts a filesystem containing the rootfs for the > > >> inner container. If that mount is nosuid then suid utilities like ping > > >> aren't going to work in the inner container. > > >> > > >> So since there's a use case for suid in a userns mount and we have what > > >> we belive are sufficient protections against using this as a vector to > > >> get privileges outside the container, I'm planning to move ahead without > > >> the MNT_NOSUID restriction. Any objections? > > > > > > In the general case how'd we prevent suid executable being tricked to > > > do something it shouldn't do by unprivileged mounting into sensitive > > > places (i.e. config files) inside the container? > > The design of the namespaces would prevent that. You cannot manipulate your > mounts namespace unless you own it. You cannot manipulate the mounts namespace > for a task whose user namespace you do not own. If you can, for instance, > bind mount $HOME/shadow onto /etc/shadow, then you already own your user > namespace and are root there, so any suid-root program which you mount through > fuse will only subjegate your own namespace. Any task which running in the > parent user-ns (and therefore parent mount-ns) will not see your bind mount. > > > > Allowing SUID looks like a slippery slope to me. And there are plenty > > > of solutions to the "ping" problem, AFAICS, that don't involve the > > > suid bit. > > > > ping isn't even suid on my system, it has security.capability xattr instead. > > security.capability xattrs that will have the exact same concerns wrt > confusion through bind mounts as suid. > > > Please just get rid of SUID/SGID. It's a legacy, it's a hack, not > > worth the complexity and potential problems arising from that > > complexity. > > Oh boy, I don't know which side to sit on here :) I'm all for replacing > suid with some use of file capabilities, but realistically there are reasons > why that hasn't happened more widely than it has - tar, package managers, > cpio, nfs, etc. Miklos: I we're all generally in agreement here that suid/sgid is not the best solution, but as Serge points out we are unfortunately not yet in a place where it can be completely dropped in favor of capabilities. In light of this can I convince you to reconsider your position? Thanks, Seth -- 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
