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	Mon, 05 Aug 2024 23:41:11 +0000
Date: Tue, 6 Aug 2024 00:41:10 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Christian Brauner <brauner@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>, jack@suse.cz,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	josef@toxicpanda.com, wojciech.gladysz@infogain.com,
	ebiederm@xmission.com, kees@kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] exec: drop a racy path_noexec check
Message-ID: <20240805234110.GJ5334@ZenIV>
References: <20240805-fehlbesetzung-nilpferd-1ed58783ad4d@brauner>
 <20240805131721.765484-1-mjguzik@gmail.com>
 <20240805-denkspiel-unruhen-c0ec00f5d370@brauner>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Tue, Aug 06, 2024 at 12:38:04AM +0100, Al Viro wrote:
> On Mon, Aug 05, 2024 at 05:35:35PM +0200, Christian Brauner wrote:
> > > To my reading that path_noexec is still there only for debug, not
> > > because of any security need.
> > 
> > I don't think it's there for debug. I think that WARN_ON_ONCE() is based
> > on the assumption that the mount properties can't change. IOW, someone
> > must've thought that somehow stable mount properties are guaranteed
> > after may_open() irrespective of how the file was opened. And in that
> > sense they thought they might actually catch a bug.
> 
> That would be a neat trick, seeing that there'd never been anything to
> prevent mount -o remount,exec while something is executed on the
                           noexec, obviously...