Quoting Andy Lutomirski (luto@xxxxxxxxxxxxxx): > On Tue, Apr 29, 2014 at 5:21 PM, Serge Hallyn <serge.hallyn@xxxxxxxxxx> wrote: > > Quoting Andy Lutomirski (luto@xxxxxxxxxxxxxx): > >> > It should be a nonissue so long as we make sure that a file owned by a > >> > uid outside the scope of the container may not be changed even though > >> > fs_owner_uid is set. Otherwise, it's just a matter of chmod +S on say > >> > a shell and anyone who can see the fs from the host will be getting a > >> > root shell (assuming said file is owned by the host's uid 0). > >> > >> I feel like that's too fragile. I'd rather add a rule that one of > > > > yeah I don't wnat to rush something like that. I'd rather stash > > the userns of the task which did the mounting and check against > > that. Note that would make it worthless unless and until we allowed > > mounting from non-init userns, but then we can only claim "our fs > > superblock readers suck and therefore containers can't mount an fs" > > so long before we start to feel some shame and audit them... > > > >> these filesystems always acts like it's nosuid unless you're inside a > >> user namespace that matches fs_owner_uid. > >> > >> Maybe even that is too weird. How about setuid, setgid, and fcaps > >> only work on mounts that are in mount namespaces that are owned by the > >> current user namespace or one of its parents? IOW, a struct mount is > >> only trusted if mnt->mnt_ns->user_ns == current user ns or one of its > >> parents? > >> > >> Untrusted mounts would act like they are nosuid,nodev. Someone can > >> try to figure out a safe way to relax nodev at some point. > > Do you like this variant? We could add a way for global root to mount > an fs on behalf of a userns. I'd rather this be more explicit than > just mounting it in a mount ns owned by the user namespace, though. I'm missing something. Which mnt are you talking about? A user can just clone a new userns and then clone(CLONE_NEWNS) to get a set of mounts owned by himself... We need to get a mnt (or a cred or straight to a userns) tied to the first mount of the superblock, istm. -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
