From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by smtp.lore.kernel.org (Postfix) with SMTP id 31CFEC41513 for ; Thu, 18 Jul 2024 12:23:19 +0000 (UTC) Received: (qmail 20102 invoked by uid 550); 18 Jul 2024 12:23:05 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 20076 invoked from network); 18 Jul 2024 12:23:05 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1721305376; bh=UuxN7bN/Fuu2OQEszjkAFQVZQifPWKBjgSrPir4Ebkw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Q+/V9E/enLZnrkKrttf8y9hOgi20C0C4HhYlV1nFcKgT0ABn2mTbB01bIrXEdykV+ 3k6/zk6VwUdg4v8pkHW46XXJ82C//bDuJflvichEl0FOm0Pfi+x1UId3Kn6shCj6Nc 20PvlnlYXxM0iXovWqaAI5pmmzDtbEaTo4i6+oa4= Date: Thu, 18 Jul 2024 14:22:49 +0200 From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= To: Andy Lutomirski Cc: Steve Dower , Jeff Xu , Al Viro , Christian Brauner , Kees Cook , Linus Torvalds , Paul Moore , Theodore Ts'o , Alejandro Colomar , Aleksa Sarai , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Christian Heimes , Dmitry Vyukov , Eric Biggers , Eric Chiang , Fan Wu , Florian Weimer , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Jordan R Abrahams , Lakshmi Ramasubramanian , Luca Boccassi , Luis Chamberlain , "Madhavan T . Venkataraman" , Matt Bobrowski , Matthew Garrett , Matthew Wilcox , Miklos Szeredi , Mimi Zohar , Nicolas Bouchinet , Scott Shell , Shuah Khan , Stephen Rothwell , Steve Grubb , Thibaut Sautereau , Vincent Strubel , Xiaoming Ni , Yin Fengwei , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Elliott Hughes Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2) Message-ID: <20240718.Niexoo0ahch0@digikod.net> References: <20240704190137.696169-1-mic@digikod.net> <20240704190137.696169-2-mic@digikod.net> <20240717.AGh2shahc9ee@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Infomaniak-Routing: alpha On Thu, Jul 18, 2024 at 09:02:56AM +0800, Andy Lutomirski wrote: > > On Jul 17, 2024, at 6:01 PM, Mickaël Salaün wrote: > > > > On Wed, Jul 17, 2024 at 09:26:22AM +0100, Steve Dower wrote: > >>> On 17/07/2024 07:33, Jeff Xu wrote: > >>> Consider those cases: I think: > >>> a> relying purely on userspace for enforcement does't seem to be > >>> effective, e.g. it is trivial to call open(), then mmap() it into > >>> executable memory. > >> > >> If there's a way to do this without running executable code that had to pass > >> a previous execveat() check, then yeah, it's not effective (e.g. a Python > >> interpreter that *doesn't* enforce execveat() is a trivial way to do it). > >> > >> Once arbitrary code is running, all bets are off. So long as all arbitrary > >> code is being checked itself, it's allowed to do things that would bypass > >> later checks (and it's up to whoever audited it in the first place to > >> prevent this by not giving it the special mark that allows it to pass the > >> check). > > > > Exactly. As explained in the patches, one crucial prerequisite is that > > the executable code is trusted, and the system must provide integrity > > guarantees. We cannot do anything without that. This patches series is > > a building block to fix a blind spot on Linux systems to be able to > > fully control executability. > > Circling back to my previous comment (did that ever get noticed?), I Yes, I replied to your comments. Did I miss something? > don’t think this is quite right: > > https://lore.kernel.org/all/CALCETrWYu=PYJSgyJ-vaa+3BGAry8Jo8xErZLiGR3U5h6+U0tA@mail.gmail.com/ > > On a basic system configuration, a given path either may or may not be > executed. And maybe that path has some integrity check (dm-verity, > etc). So the kernel should tell the interpreter/loader whether the > target may be executed. All fine. > > But I think the more complex cases are more interesting, and the > “execute a program” process IS NOT BINARY. An attempt to execute can > be rejected outright, or it can be allowed *with a change to creds or > security context*. It would be entirely reasonable to have a policy > that allows execution of non-integrity-checked files but in a very > locked down context only. I guess you mean to transition to a sandbox when executing an untrusted file. This is a good idea. I talked about role transition in the patch's description: With the information that a script interpreter is about to interpret a script, an LSM security policy can adjust caller's access rights or log execution request as for native script execution (e.g. role transition). This is possible thanks to the call to security_bprm_creds_for_exec(). > > So… shouldn’t a patch series to this effect actually support this? > This patch series brings the minimal building blocks to have a consistent execution environment. Role transitions for script execution are left to LSMs. For instance, we could extend Landlock to automatically sandbox untrusted scripts.