linux-kernel - Re: [PATCH] vfs: relax linkat() AT_EMPTY_PATH - aka flink()

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Message-ID: <20240412-zander-graustufen-bf63bbaa88fd@brauner>
Date: Fri, 12 Apr 2024 08:44:21 +0200
From: Christian Brauner <brauner@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Charles Mirabile <cmirabil@...hat.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Andrew Lutomirski <luto@...nel.org>, Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH] vfs: relax linkat() AT_EMPTY_PATH - aka flink() -
 requirements

On Thu, Apr 11, 2024 at 11:13:53AM -0700, Linus Torvalds wrote:
> On Thu, 11 Apr 2024 at 10:35, Charles Mirabile <cmirabil@...hat.com> wrote:
> >
> > And a slightly dubious addition to bypass these checks for tmpfiles
> > across the board.
> 
> Does this make sense?
> 
> I 100% agree that one of the primary reasons why people want flink()
> is that "open tmpfile, finalize contents and permissions, then link
> the final result into the filesystem".
> 
> But I would expect that the "same credentials as open" check is the
> one that really matters.

Yes. There's no need to give O_TMPFILE special status there. We also end
up with a collection of special-cases which is just unpleasant.