linux-kernel - Re: [PATCH] utimensat() non-conformances and fixes [v3]

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Date:	Tue, 3 Jun 2008 13:10:15 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Miklos Szeredi <miklos@...redi.hu>, drepper@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-man@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] utimensat() non-conformances and fixes [v3]

Al Viro wrote:
> On Tue, Jun 03, 2008 at 01:01:35PM +0100, Jamie Lokier wrote:
> > > with a lot of things, starting with "why utimes(2) has weaker requirements
> > > with NULL argument", but we are far too late to fix that.
> > 
> > To be fair, having a writable file descriptor only lets you change the
> > mtime to "now", and having a readable file descriptor only lets you
> > change the atime to "now".
> > 
> > Changing the times _in general_ can be seen as over-reaching those
> > capabilities and arguably justifies more strict checks.
> 
> Which is what all questions about writability apply only to NULL case
> anyway...

Oh!

So if I have the file descriptor, I can just as well change the mtime
by read a byte and write it back.  Or even do a zero-length write, on
some OSes.

-- Jamie
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