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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC05AC3DA42 for ; Wed, 10 Jul 2024 10:05:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5CDD66B0092; Wed, 10 Jul 2024 06:05:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 57DE56B0095; Wed, 10 Jul 2024 06:05:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 445466B0096; Wed, 10 Jul 2024 06:05:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 27E8A6B0092 for ; Wed, 10 Jul 2024 06:05:15 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id C4F58A493B for ; Wed, 10 Jul 2024 10:05:14 +0000 (UTC) X-FDA: 82323410148.06.C4E155D Received: from smtp-bc0d.mail.infomaniak.ch (smtp-bc0d.mail.infomaniak.ch [45.157.188.13]) by imf07.hostedemail.com (Postfix) with ESMTP id 6AEF540012 for ; Wed, 10 Jul 2024 10:05:12 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=digikod.net header.s=20191114 header.b=DNVbx2ud; spf=pass (imf07.hostedemail.com: domain of mic@digikod.net designates 45.157.188.13 as permitted sender) smtp.mailfrom=mic@digikod.net; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1720605871; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=58eL5zKFVrJFUT+TpbxjO2RgasvOa3v7FdFqIaHbAZ8=; b=qlqncBPhXrFu0pFHl4cSIHgmWfPr4ofyWh0mA8fgT7QV3rPanJWEx0GXIRf2xtSAFELCRB 8NezXH8U5rzxy195XJh4zR1UjTPL8A114fqPxpWxZK1mOaWZ7EeSfOUYZpBxQ3nqprWw1M /LE1f0Mf4rFb6FdOS2Lu/AYveBPTt9A= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=digikod.net header.s=20191114 header.b=DNVbx2ud; spf=pass (imf07.hostedemail.com: domain of mic@digikod.net designates 45.157.188.13 as permitted sender) smtp.mailfrom=mic@digikod.net; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1720605871; a=rsa-sha256; cv=none; b=DnfxxUTYGojKTeI1cJnehEB5IN5keyQ0280VTMSGRp4tRpTQU6tZlYBzypELXQuuU59YRT L79jLIuum6aMKj1z861TkMOAJsqLiHdjvdanE2e21wAHHhpcqp4cg35cZxdGntSBj62bRf 7vkIrIvyfKheT+eUHDA6Tmr5oioMI5I= Received: from smtp-3-0001.mail.infomaniak.ch (smtp-3-0001.mail.infomaniak.ch [10.4.36.108]) by smtp-4-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4WJtlB1RbmzSKT; Wed, 10 Jul 2024 12:05:10 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1720605910; bh=58eL5zKFVrJFUT+TpbxjO2RgasvOa3v7FdFqIaHbAZ8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DNVbx2udibxVu+14OKvyFsM2tte1G7+GSl8Z+NOcHcVVvvBg1ydxpZsw6h/1RkTaN ejzvZofhsiG9dNul4ThaAxY28YALObLrSzblZ8Zjk8uwQdQKc/EuaduylSGnGw3pZ7 LEta7bCt/CqWCCKmMGDr9F+uKDtZtEAT6JChcVeQ= Received: from unknown by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4WJtl848ghzL4p; Wed, 10 Jul 2024 12:05:08 +0200 (CEST) Date: Wed, 10 Jul 2024 12:05:05 +0200 From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= To: Florian Weimer Cc: 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 , Geert Uytterhoeven , James Morris , Jan Kara , Jann Horn , Jeff Xu , 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 Dower , 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, Eric Biederman , linux-mm@kvack.org Subject: Re: [PATCH] binfmt_elf: Fail execution of shared objects with ELIBEXEC (was: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)) Message-ID: <20240710.Lu2thiemeil2@digikod.net> References: <20240704190137.696169-1-mic@digikod.net> <20240704190137.696169-2-mic@digikod.net> <87bk3bvhr1.fsf@oldenburg.str.redhat.com> <20240706.poo9ahd3La9b@digikod.net> <871q46bkoz.fsf@oldenburg.str.redhat.com> <20240708.zooj9Miaties@digikod.net> <878qybet6t.fsf_-_@oldenburg.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <878qybet6t.fsf_-_@oldenburg.str.redhat.com> X-Infomaniak-Routing: alpha X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 6AEF540012 X-Stat-Signature: oxj83ke6p891w1d9wpf5bkiumni88ub6 X-Rspam-User: X-HE-Tag: 1720605912-470756 X-HE-Meta: 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 Np3jb/Jj m5h87a6SFVe9jZU/qNc5FEKNJbIYSEefLuIeBJyGetNuf9x0zyzYWG3A+mULFEstmk7fP+3UpvEeDof8fAIlu6QttNGl27FfHwlm28yvHyc8/+KhusX+ip3wehY8vxGIbuUjGV5FeXsVAiekRhUSYegOzzenWzSbtDgDpyaSzYbbMlmcRglSWydU5ChNkWQlgBAv/wQIEe4WZcH6HPMfdVnNKRPlpWtz7LLth5VFdpekdUSR6TrvuAIKJFrP8o/jcqWPJpUX0gOPW6e378XKhLqJKY9RCI/0Bkny8LqsbSxQKtDKF4SYoFajYkS6CqAMho13yI+GUSdMWDhF0NFJ+kpv8dBnssjVg0CRFmha1HaMj+34= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 08, 2024 at 06:37:14PM +0200, Florian Weimer wrote: > * Mickaël Salaün: > > > On Sat, Jul 06, 2024 at 05:32:12PM +0200, Florian Weimer wrote: > >> * Mickaël Salaün: > >> > >> > On Fri, Jul 05, 2024 at 08:03:14PM +0200, Florian Weimer wrote: > >> >> * Mickaël Salaün: > >> >> > >> >> > Add a new AT_CHECK flag to execveat(2) to check if a file would be > >> >> > allowed for execution. The main use case is for script interpreters and > >> >> > dynamic linkers to check execution permission according to the kernel's > >> >> > security policy. Another use case is to add context to access logs e.g., > >> >> > which script (instead of interpreter) accessed a file. As any > >> >> > executable code, scripts could also use this check [1]. > >> >> > >> >> Some distributions no longer set executable bits on most shared objects, > >> >> which I assume would interfere with AT_CHECK probing for shared objects. > >> > > >> > A file without the execute permission is not considered as executable by > >> > the kernel. The AT_CHECK flag doesn't change this semantic. Please > >> > note that this is just a check, not a restriction. See the next patch > >> > for the optional policy enforcement. > >> > > >> > Anyway, we need to define the policy, and for Linux this is done with > >> > the file permission bits. So for systems willing to have a consistent > >> > execution policy, we need to rely on the same bits. > >> > >> Yes, that makes complete sense. I just wanted to point out the odd > >> interaction with the old binutils bug and the (sadly still current) > >> kernel bug. > >> > >> >> Removing the executable bit is attractive because of a combination of > >> >> two bugs: a binutils wart which until recently always set the entry > >> >> point address in the ELF header to zero, and the kernel not checking for > >> >> a zero entry point (maybe in combination with an absent program > >> >> interpreter) and failing the execve with ELIBEXEC, instead of doing the > >> >> execve and then faulting at virtual address zero. Removing the > >> >> executable bit is currently the only way to avoid these confusing > >> >> crashes, so I understand the temptation. > >> > > >> > Interesting. Can you please point to the bug report and the fix? I > >> > don't see any ELIBEXEC in the kernel. > >> > >> The kernel hasn't been fixed yet. I do think this should be fixed, so > >> that distributions can bring back the executable bit. > > > > Can you please point to the mailing list discussion or the bug report? > > I'm not sure if this was ever reported upstream as an RFE to fail with > ELIBEXEC. We have downstream bug report: > > Prevent executed .so files with e_entry == 0 from attempting to become > a process. > Thanks for the info. > > I've put together a patch which seems to work, see below. > > I don't think there's any impact on AT_CHECK with execveat because that > mode will never get to this point. Correct, that is not an issue for AT_CHECK use cases.