linux-kernel - Re: procfs: open("/proc/self/fd/...") allows bypassing O

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Message-ID: <03l0hfZIzD9KwSxSntGcmfFhvbIKiK45poGUhXtR7Qi0Av0-ZnqnSBPAP09GGpSrKGZWZNCTvme_Gpiuz0Bcg6ewDIXSH24SBx_tvfyZSWU=@emersion.fr>
Date:   Thu, 12 May 2022 12:41:16 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: procfs: open("/proc/self/fd/...") allows bypassing O_RDONLY

On Thursday, May 12th, 2022 at 12:37, Simon Ser <contact@...rsion.fr> wrote:

> what would be a good way to share a FD to another
> process without allowing it to write to the underlying file?

(I'm reminded that memfd + seals exist for this purpose. Still, I'd be
interested to know whether that O_RDONLY/O_RDWR behavior is intended,
because it's pretty surprising. The motivation for using O_RDONLY over
memfd seals is that it isn't Linux-specific.)