linux-ext4 - Re: [v8 4/5] ext4: adds FS_IOC_FSSETXATTR/FS_IOC

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Date:	Thu, 5 Feb 2015 17:38:15 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Andy Lutomirski <luto@...capital.net>,
	Li Xi <pkuelelixi@...il.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger@...ger.ca>, Jan Kara <jack@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>, dmonakhov@...nvz.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [v8 4/5] ext4: adds FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR
 interface support

  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@...e.cz>
SUSE Labs, CR
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