Re: [v8 4/5] ext4: adds FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR interface support

[Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>]

  Hello,

> Users have *always* been allowed to set the project ID of
> their own files. How else are they going to set the project ID on
> files they create in random directories so to account them to the
> correct project they are working on?
> 
> However, you keep making the assumption that project quotas ==
> directory subtree quotas.  Project quotas are *not limited* to
> directory subtrees - the subtree quota implementation is just an
> implementation that *sets the default project ID* on files as they
> are created.
> 
> e.g. there are production systems out there where project quotas are
> used to track home directory space usage rather than user quotas.
> This means users can take actions like "this file actually belongs
> to project X and it shouldn't be accounted against my home
> directory". Users can create their own sub directories that account
> everything by default to project X rather than their own home
> directory.
> 
> Again: project quotas are an *accounting* mechanism, not a security
> mechanism.
  OK, but now I got confused ;) So if users can change project ID of files
they own, what's the point of project quotas? If I need to create a file
and project quota doesn't allow me, I just set its project ID to some
random number and I'm done with that... So are really project quotas just
"advisory" - i.e., all users of a system cooperate so that project X
doesn't use more space than it should (and project quotas make this
cooperation somewhat simpler) or is there something which limits which
project IDs user can set? I didn't find anything...

								Honza
-- 
Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
SUSE Labs, CR