Quoting Miklos Szeredi (miklos@xxxxxxxxxx): > > I'm a bit lost about what is currently done and who advocates for what. > > > > It seems to me the MNT_ALLOWUSERMNT (or whatever :) flag should be > > propagated. In the /share rbind+chroot example, I assume the admin > > would start by doing > > > > mount --bind /share /share > > mount --make-slave /share > > mount --bind -o allow_user_mounts /share (or whatever) > > mount --make-shared /share > > > > then on login, pam does > > > > chroot /share/$USER > > > > or some sort of > > > > mount --bind /share /home/$USER/root > > chroot /home/$USER/root > > > > or whatever. In any case, the user cannot make user mounts except under > > /share, and any cloned namespaces will still allow user mounts. > > I don't quite understand your method. This is how I think of it: > > mount --make-rshared / > mkdir -p /mnt/ns/$USER > mount --rbind / /mnt/ns/$USER > mount --make-rslave /mnt/ns/$USER This was my main point - that the tree in which users can mount will be a slave of /, so that propagating the "are user mounts allowed" flag among peers is safe and intuitive. > mount --set-flags --recursive -oallowusermnt /mnt/ns/$USER > chroot /mnt/ns/$USER > su - $USER > > I did actually try something equivalent (without the fancy mount > commands though), and it worked fine. The only "problem" is the > proliferation of mounts in /proc/mounts. There was a recently posted > patch in AppArmor, that at least hides unreachable mounts from > /proc/mounts, so the user wouldn't see all those. But it could still > be pretty confusing to the sysadmin. > > So in that sense doing it the complicated way, by first cloning the > namespace, and then copying and sharing mounts individually which need > to be shared could relieve this somewhat. True. But the kernel functionality you provide enables both ways so no problem in either case :) > Another point: user mounts under /proc and /sys shouldn't be allowed. > There are files there (at least in /proc) that are seemingly writable > by the user, but they are still not writable in the sense, that > "normal" files are. Good point. > Anyway, there are lots of userspace policy issues, but those don't > impact the kernel part. Though it might make sense to enforce /proc and /sys not allowing user mounts under them in the kernel. > As for the original question of propagating the "allowusermnt" flag, I > think it doesn't matter, as long as it's consistent and documented. > > Propagating some mount flags and not propagating others is > inconsistent and confusing, so I wouldn't want that. Currently > remount doesn't propagate mount flags, that may be a bug, dunno. Dave, any thoughts on safety of propagating the vfsmount read-only flags? -serge - 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
