linux-kernel - Re: [NFS] [PATCH 2/7] NFS: if ATTR_KILL_S*ID bits are set, then skip mode change

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Date:	Fri, 14 Sep 2007 20:25:45 +1000
From:	Greg Banks <gnb@....com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	nfs@...ts.sourceforge.net, unionfs@...esystems.org,
	linux-cifs-client@...ts.samba.org,
	ecryptfs-devel@...ts.sourceforge.net,
	reiserfs-devel@...r.kernel.org
Subject: Re: [NFS] [PATCH 2/7] NFS: if ATTR_KILL_S*ID bits are set, then skip mode change

On Tue, Sep 04, 2007 at 10:37:04AM -0400, Jeff Layton wrote:
> If the ATTR_KILL_S*ID bits are set then any mode change is only for
> clearing the setuid/setgid bits. For NFS skip the mode change and
> let the server handle it.

You're assuming the server will remove setuid and setgid bits on WRITE?
I don't see that behaviour specified in the RFC, at least for v3.
The RFC specifies a behaviour for the mtime attribute as a side
effect of WRITE, but says nothing about mode.  This means server
implementations are free to clobber setuid or not.  A quick experiment
shows that at least the Irix server will *NOT* clobber those bits.
So with an Irix server you've now lost this Linux-specific "security
feature".

I'm curious about the reasons behind this change.  You mention
credential issues; how exactly is it that you have the correct creds
to perform a WRITE rpc but not a SETATTR rpc?

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
Apparently, I'm Bedevere.  Which MPHG character are you?
I don't speak for SGI.
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