linux-kernel - Re: [PATCH v3 1/2] exec: add PR_HIDE_SELF

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Message-Id: <1557ec53-2d9b-4f5d-b144-01ed0dd3c7a6@app.fastmail.com>
Date:   Mon, 30 Jan 2023 16:52:55 -0500
From:   "Colin Walters" <walters@...bum.org>
To:     "Christian Brauner" <brauner@...nel.org>
Cc:     "Giuseppe Scrivano" <gscrivan@...hat.com>,
        "Aleksa Sarai" <cyphar@...har.com>, linux-kernel@...r.kernel.org,
        "Kees Cook" <keescook@...omium.org>, bristot@...hat.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Al Viro" <viro@...iv.linux.org.uk>,
        "Alexander Larsson" <alexl@...hat.com>,
        "Peter Zijlstra" <peterz@...radead.org>, bmasney@...hat.com
Subject: Re: [PATCH v3 1/2] exec: add PR_HIDE_SELF_EXE prctl

On Mon, Jan 30, 2023, at 5:06 AM, Christian Brauner wrote:

> The good thing is that - even if it will take a longer - that Aleksa's
> patchset will provide a more general solution by making it possible for
> runc/crun/lxc to open the target binary with a restricted upgrade mask
> making it impossible to open the binary read-write again. This won't
> break criu and will fix this issue and is generally useful.

Had to go back up thread more carefully; looking at the referenced commits now in
https://github.com/cyphar/linux/commits/magiclink/open_how-reopen
I do agree that that direction is the most elegant.  The main downside I can think of is the potential blast radius is larger, and more nontrivial code.  

But...in practice I guess today for the runc/crun type attacks today there are commonly multiple mitigations (e.g. read-only rootfs, multiple LSMs, and finally the memfd copy fallback) so we can probably wait for that patchset to land.

In short: agreed!