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

[Greg Banks <gnb@sgi.com>]

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.