On Tue, 2007-04-17 at 19:44 +0200, Miklos Szeredi wrote: > > 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 > mount --set-flags --recursive -oallowusermnt /mnt/ns/$USER > chroot /mnt/ns/$USER > su - $USER > > I did actually try something equivalent (without the fancy mount > commands though), and it worked fine. The only "problem" is the > proliferation of mounts in /proc/mounts. There was a recently posted > patch in AppArmor, that at least hides unreachable mounts from > /proc/mounts, so the user wouldn't see all those. But it could still > be pretty confusing to the sysadmin. unbindable mounts were designed to overcome the proliferation problem. Your steps should be something like this: mount --make-rshared / mkdir -p /mnt/ns mount --bind /mnt/ns /mnt/ns mount --make-unbindable /mnt/ns mkdir -p /mnt/ns/$USER mount --rbind / /mnt/ns/$USER mount --make-rslave /mnt/ns/$USER mount --set-flags --recursive -oallowusermnt /mnt/ns/$USER chroot /mnt/ns/$USER su - $USER try this and your proliferation problem will disappear. :-) > > 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. the unbindable mount will just provide you permanent relief. > > 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. > > Anyway, there are lots of userspace policy issues, but those don't > impact the kernel part. > > 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, For consistency reason, one can propagate all the flags. But propagating only those flags that interfere with shared-subtree semantics should suffice. wait...Dave's read-only bind mounts infact need the ability to selectively make some mounts readonly. In such cases propagating the read-only flag will just step on Dave's feature. Wont' it? RP > > Miklos - 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
