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

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Message-ID: <20230129165812.sqypj6nzam7o33lf@wittgenstein>
Date:   Sun, 29 Jan 2023 17:58:12 +0100
From:   Christian Brauner <brauner@...nel.org>
To:     Colin Walters <walters@...bum.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 Sun, Jan 29, 2023 at 08:59:32AM -0500, Colin Walters wrote:
> 
> 
> On Wed, Jan 25, 2023, at 11:30 AM, Giuseppe Scrivano wrote:
> > 
> > After reading some comments on the LWN.net article, I wonder if
> > PR_HIDE_SELF_EXE should apply to CAP_SYS_ADMIN in the initial user
> > namespace or if in this case root should keep the privilege to inspect
> > the binary of a process.  If a container runs with that many privileges
> > then it has already other ways to damage the host anyway.
> 
> Right, that's what I was trying to express with the "make it work the same as map_files".  Hiding the entry entirely even for initial-namespace-root (real root) seems like it's going to potentially confuse profiling/tracing/debugging tools for no good reason.

If this can be circumvented via CAP_SYS_ADMIN then this mitigation
becomes immediately way less interesting because the userspace
mitigation we came up with protects against CAP_SYS_ADMIN as well
without any regression risk. At which point this is only useful for some
privileged sandboxes at what point this isn't worth it.

I'm still looking at userspace codebases to ensure that this is a change
we can risk in general as this has the potential to prevent criu from
dumping such processes. I'll talk to them tomorrow anyway.