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Message-ID: <20200430015429.wuob7m5ofdewubui@yavin.dot.cyphar.com>
Date: Thu, 30 Apr 2020 11:54:29 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...nel.org>,
Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Eric Chiang <ericchiang@...gle.com>,
Florian Weimer <fweimer@...hat.com>,
James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>,
Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Matthew Garrett <mjg59@...gle.com>,
Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mickaël Salaün <mickael.salaun@....gouv.fr>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] Add support for RESOLVE_MAYEXEC
On 2020-04-28, Mickaël Salaün <mic@...ikod.net> wrote:
> The goal of this patch series is to enable to control script execution
> with interpreters help. A new RESOLVE_MAYEXEC flag, usable through
> openat2(2), is added to enable userspace script interpreter to delegate
> to the kernel (and thus the system security policy) the permission to
> interpret/execute scripts or other files containing what can be seen as
> commands.
>
> This third patch series mainly differ from the previous one by relying
> on the new openat2(2) system call to get rid of the undefined behavior
> of the open(2) flags. Thus, the previous O_MAYEXEC flag is now replaced
> with the new RESOLVE_MAYEXEC flag and benefits from the openat2(2)
> strict check of this kind of flags.
My only strong upfront objection is with this being a RESOLVE_ flag.
RESOLVE_ flags have a specific meaning (they generally apply to all
components, and affect the rules of path resolution). RESOLVE_MAYEXEC
does neither of these things and so seems out of place among the other
RESOLVE_ flags.
I would argue this should be an O_ flag, but not supported for the
old-style open(2). This is what the O_SPECIFIC_FD patchset does[1] and I
think it's a reasonable way of solving such problems.
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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