> > On Sat, 21 Apr 2007 10:09:42 +0200 Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >
> >> > > +static bool permit_umount(struct vfsmount *mnt, int flags)
> >> > > +{
> >> > >
> >> > > ...
> >> > >
> >> > > + return mnt->mnt_uid == current->uid;
> >> > > +}
> >> >
> >> > Yes, this seems very wrong. I'd have thought that comparing user_struct*'s
> >> > would get us a heck of a lot closer to being able to support aliasing of
> >> > UIDs between different namespaces.
> >> >
> >>
> >> OK, I'll fix this up.
> >>
> >> Actually an earlier version of this patch did use user_struct's but
> >> I'd changed it to uids, because it's simpler.
> >
> > OK..
> >
> >> I didn't think about
> >> this being contrary to the id namespaces thing.
> >
> > Well I was madly assuming that when serarate UID namespaces are in use, UID
> > 42 in container A will have a different user_struct from UID 42 in
> > container B. I'd suggest that we provoke an opinion from Eric & co before
> > you do work on this.
>
> That is what I what I have been thinking as well,
Does this mean, that containers will need this? Or that you don't
know yet?
> storing a user struct on each mount point seems sane, plus it allows
> per user mount rlimits which is major plus. Especially since we
> seem to be doing accounting only for user mounts a per user rlimit
> seems good.
I'm not against per-user rlimits for mounts, but I'd rather do this
later...
> To get the user we should be user fs_uid as HPA suggested.
fsuid is exclusively used for checking file permissions, which we
don't do here anymore. So while it could be argued, that mount() _is_
a filesystem operation, it is really a different sort of filesystem
operation than the rest.
OTOH it wouldn't hurt to use fsuid instead of ruid...
> Finally I'm pretty certain the capability we should care about in
> this context is CAP_SETUID. Instead of CAP_SYS_ADMIN.
>
> If we have CAP_SETUID we can become which ever user owns the mount,
> and the root user in a container needs this, so he can run login
> programs. So changing the appropriate super user checks from
> CAP_SYS_ADMIN to CAP_SETUID I think is the right thing todo.
That's a flawed logic. If you want to mount as a specific user, and
you have CAP_SETUID, then just use set*uid() and then mount().
Changing the capability check for mount() would break the userspace
ABI.
Miklos
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