linux-kernel - Re: [PATCH v4 2/5] fs: Add fchmodat2()

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Message-ID: <20230727163103.GB20050@brightrain.aerifal.cx>
Date:   Thu, 27 Jul 2023 12:31:04 -0400
From:   "dalias@...c.org" <dalias@...c.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Aleksa Sarai' <cyphar@...har.com>,
        Alexey Gladkov <legion@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
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        Palmer Dabbelt <palmer@...ive.com>
Subject: Re: [PATCH v4 2/5] fs: Add fchmodat2()

On Thu, Jul 27, 2023 at 09:01:06AM +0000, David Laight wrote:
> From: Aleksa Sarai
> > Sent: 25 July 2023 17:36
> ....
> > We almost certainly want to support AT_EMPTY_PATH at the same time.
> > Otherwise userspace will still need to go through /proc when trying to
> > chmod a file handle they have.
> 
> That can't be allowed.
> 
> Just because a process has a file open and write access to
> the directory that contains it doesn't mean they are allowed
> to change the file permissions.
> 
> They also need directory search access from a directory
> they have open through to the containing directory.

Am I missing something? How is this different from fchmod?

Rich