linux-ext4 - Re: [fuse-devel] [PATCH 01/25] VFS: move attr_kill logic from notify

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Date:	Mon, 06 Aug 2007 17:23:39 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jlayton@...hat.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, codalist@...emann.coda.cs.cmu.edu,
	cluster-devel@...hat.com, jfs-discussion@...ts.sourceforge.net,
	mikulas@...ax.karlin.mff.cuni.cz, zippel@...ux-m68k.org,
	xfs@....sgi.com, joel.becker@...cle.com, wli@...omorphy.com,
	reiserfs-devel@...r.kernel.org, dhowells@...hat.com,
	fuse-devel@...ts.sourceforge.net, jffs-dev@...s.com,
	user-mode-linux-user@...ts.sourceforge.net,
	v9fs-developer@...ts.sourceforge.net, linux-ext4@...r.kernel.org,
	linux-cifs-client@...ts.samba.org, ocfs2-devel@....oracle.com,
	bfennema@...con.csc.calpoly.edu
Subject: Re: [fuse-devel] [PATCH 01/25] VFS: move attr_kill logic from
	notify_change into helper function

On Mon, 2007-08-06 at 21:37 +0200, Miklos Szeredi wrote:
> > > Your patch is changing the API in a very unsafe way, since there will
> > > be no error or warning on an unconverted fs.  And that could lead to
> > > security holes.
> > > 
> > > If we would rename the setattr method to setattr_new as well as
> > > changing it's behavior, that would be fine.  But I guess we do not
> > > want to do that.
> > 
> > Which "unconverted fses"? If we're talking out of tree stuff, then too
> > bad: it is _their_ responsibility to keep up with kernel changes.
> 
> It is usually a good idea to not change the semantics of an API in a
> backward incompatible way without changing the syntax as well.

We're taking two setattr flags ATTR_KILL_SGID, and ATTR_KILL_SUID which
have existed for several years in the VFS, and making them visible to
the filesystems. Out-of-tree filesystems that care can check for them in
a completely backward compatible way: you don't even need to add a
#define.

> This is true regardless of whether we care about out-of-tree code or
> not (and we should care to some degree).  And especially true if the
> change in question is security sensitive.

It is not true "regardless": the in-tree code is being converted.
Out-of-tree code is the only "problem" here, and their only problem is
that they may have to add support for the new flags if they also support
suid/sgid mode bits.

Are you advocating reserving a new filesystem bit every time we need to
add an attribute flag?

Trond

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