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    SubjectRe: [Devel] Re: [patch 05/10] add "permit user mounts in new namespace" clone flag
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    > > > > I've tried to make this unprivileged mount thing as simple as
    > > > > possible, and no simpler. If we can make it even simpler, all the
    > > > > better.
    > > >
    > > > We are certainly much more complex then the code in plan9 (just
    > > > read through it) so I think we have room for improvement.
    > > >
    > > > Just for reference what I saw in plan 9 was:
    > > > - No super user checks in it's mount, unmount, or namespace creation paths.
    > > > - A flag to deny new mounts but not new bind mounts (for administrative purposes
    > > > the comment said).
    > > >
    > > > Our differences from plan9.
    > > > - suid capable binaries. (SUID please go away).
    > > > - A history of programs assuming only root could call mount/unmount.
    > >
    > > I hate suid as well. _The_ motivation behind this patchset was to get
    > > rid of "fusermount", a suid mount helper for fuse.
    > >
    > > But I don't think suid is going away, and definitely not overnight.
    > > Also I don't think we want to require auditing userspace before
    > > enabling user mounts.
    > >
    > > If I understand correctly, your proposal is to get rid of MNT_USER and
    > > MNT_ALLOWUSERMNT and allow/deny unprivileged mounts and umounts based
    > > on a boolean sysctl flag and on a check if the target namespace is the
    > > initial namespace or not. And maybe add some extra checks which
    > > prevent ugliness from happening with suid programs. Is this correct?
    > >
    > > If so, how are we going to make sure this won't break existing
    > > userspace without doing a full audit of all suid programs in every
    > > distro that wants this feature?
    > >
    > > Also how are we going to prevent the user from creating millions of
    > > mounts, and using up all the kernel memory for vfsmounts?
    >
    > Don't forget that almost all mount flags are per-superblock. How are you
    > planning on dealing with the case that one user mounts a filesystem
    > read-only, while another is trying to mount the same one read-write?

    Yeah, I forgot, the per-mount read-only patches are not yet in.

    That doesn't really change my agrument though. _If_ the flag is per
    mount, then it makes sense to be able to change it on a master and not
    on a slave. If mount flags are propagated, this is not possible.

    Miklos
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