linux-kernel - Re: [PATCH] exec: drop a racy path

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Message-ID: <20240805234110.GJ5334@ZenIV>
Date: Tue, 6 Aug 2024 00:41:10 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Christian Brauner <brauner@...nel.org>
Cc: Mateusz Guzik <mjguzik@...il.com>, jack@...e.cz,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	josef@...icpanda.com, wojciech.gladysz@...ogain.com,
	ebiederm@...ssion.com, kees@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH] exec: drop a racy path_noexec check

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...