Re: [patch] unprivileged mounts update
From: Serge E. Hallyn
Date: Thu Apr 26 2007 - 22:11:06 EST
Quoting Miklos Szeredi (miklos@xxxxxxxxxx):
> > Quoting Miklos Szeredi (miklos@xxxxxxxxxx):
> > > > So then as far as you're concerned, the patches which were in -mm will
> > > > remain unchanged?
> > >
> > > Basically yes. I've merged the update patch, which was not yet added
> > > to -mm, did some cosmetic code changes, and updated the patch headers.
> > >
> > > There's one open point, that I think we haven't really explored, and
> > > that is the propagation semantics. I think you had the idea, that a
> > > propagated mount should inherit ownership from the parent into which
> > > it was propagated.
> > Don't think that was me. I stayed out of those early discussions
> > because I wasn't comfortable guessing at the proper semantics yet.
> Yes, sorry, it was Eric's suggestion.
> > But really, I, as admin, have to set up both propagation and user mounts
> > for a particular subtree, so why would I *not* want user mounts to be
> > propagated?
> > So, in my own situation, I have done
> > make / rshared
> > mount --bind /share /share
> > make /share unbindable
> > for u in $users; do
> > mount --rbind / /share/$u/root
> > make /share/$u/root rslave
> > make /share/$u/root rshared
> > mount --bind -o user=$u /share/$u/root/home/$u /share/$u/root/home/$u
> > done
> > All users get chrooted into /share/$USER/root, some also get their own
> > namespace. Clearly if a user in a new namespace does
> > mount --bind -o user=me ~/somedir ~/otherdir
> > then logs out, and logs back in, I want the ~/otherdir in the new
> > namespace (and the one in the 'init' namespace) to also be owned by
> > 'me'.
> > > That sounds good if everyone agrees?
> > I've shown where I think propagating the mount owner is useful. Can you
> > detail a scenario where doing so would be bad? Then we can work toward
> > semantics that make sense...
> But in your example, the "propagated mount inherits ownership from
> parent mount" would also work, since in all namespaces the owner of
> the parent would necessary be "me".
> The "inherits parent" semantics would work better for example in the
> "all nosuid" namespace, where the user is free to modify it's mount
> If for example propagation is set up from the initial namespace to
> this user's namespace and a new mount is added to the initial
> namespace, it would be nice if the propagated new mount would also be
> owned by the user (and be "nosuid" of course).
ok, so in the example i gave, this would be the admin in the
initial namespace mounting something under /home/$USER/, which
gets propagated to slave /share/$USER/root/home/$USER, where
we would want a different mount owner.
> Does the above make sense? I'm not sure I've explained clearly
I think I see. Sounds like inherit from parent does the right thing
all around, at least in cases we've thought of so far.
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