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 X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 720BBC43331 for ; Fri, 6 Sep 2019 19:43:57 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id B2CA12178F for ; Fri, 6 Sep 2019 19:43:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZLlJ/9IR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2CA12178F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-16864-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 22368 invoked by uid 550); 6 Sep 2019 19:43:50 -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 22329 invoked from network); 6 Sep 2019 19:43:49 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567799016; bh=ALyNp3XcRSlV1veUdTZyS37yI/5XROmEBPXmdB9FYx4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ZLlJ/9IRcMsHvRjRaWN0d9mSVEKCiZFHur+ATf+fp4xj2Rl+snYyPCX41v5rHFTLI rD0BA6rDVyioR2ei5h6gk01qCm5Bwxf7EytRZkPsj6+Bv+1R03mWzrDgo1+FZcm9kF /c8ilg0uGXLLIhwX9Goa/g33Kbe2Soke3SrCr+5A= Message-ID: Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() From: Jeff Layton To: Aleksa Sarai Cc: =?ISO-8859-1?Q?Micka=EBl_Sala=FCn?= , Florian Weimer , =?ISO-8859-1?Q?Micka=EBl_Sala=FCn?= , linux-kernel@vger.kernel.org, Alexei Starovoitov , Al Viro , Andy Lutomirski , Christian Heimes , Daniel Borkmann , Eric Chiang , James Morris , Jan Kara , Jann Horn , Jonathan Corbet , Kees Cook , Matthew Garrett , Matthew Wilcox , Michael Kerrisk , Mimi Zohar , Philippe =?ISO-8859-1?Q?Tr=E9buchet?= , Scott Shell , Sean Christopherson , Shuah Khan , Song Liu , Steve Dower , Steve Grubb , Thibaut Sautereau , Vincent Strubel , Yves-Alexis Perez , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org Date: Fri, 06 Sep 2019 15:43:33 -0400 In-Reply-To: <20190906171335.d7mc3no5tdrcn6r5@yavin.dot.cyphar.com> References: <20190906152455.22757-1-mic@digikod.net> <20190906152455.22757-2-mic@digikod.net> <87ef0te7v3.fsf@oldenburg2.str.redhat.com> <75442f3b-a3d8-12db-579a-2c5983426b4d@ssi.gouv.fr> <20190906171335.d7mc3no5tdrcn6r5@yavin.dot.cyphar.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sat, 2019-09-07 at 03:13 +1000, Aleksa Sarai wrote: > On 2019-09-06, Jeff Layton wrote: > > On Fri, 2019-09-06 at 18:06 +0200, Mickaël Salaün wrote: > > > On 06/09/2019 17:56, Florian Weimer wrote: > > > > Let's assume I want to add support for this to the glibc dynamic loader, > > > > while still being able to run on older kernels. > > > > > > > > Is it safe to try the open call first, with O_MAYEXEC, and if that fails > > > > with EINVAL, try again without O_MAYEXEC? > > > > > > The kernel ignore unknown open(2) flags, so yes, it is safe even for > > > older kernel to use O_MAYEXEC. > > > > > > > Well...maybe. What about existing programs that are sending down bogus > > open flags? Once you turn this on, they may break...or provide a way to > > circumvent the protections this gives. > > It should be noted that this has been a valid concern for every new O_* > flag introduced (and yet we still introduced new flags, despite the > concern) -- though to be fair, O_TMPFILE actually does have a > work-around with the O_DIRECTORY mask setup. > > The openat2() set adds O_EMPTYPATH -- though in fairness it's also > backwards compatible because empty path strings have always given ENOENT > (or EINVAL?) while O_EMPTYPATH is a no-op non-empty strings. > > > Maybe this should be a new flag that is only usable in the new openat2() > > syscall that's still under discussion? That syscall will enforce that > > all flags are recognized. You presumably wouldn't need the sysctl if you > > went that route too. > > I'm also interested in whether we could add an UPGRADE_NOEXEC flag to > how->upgrade_mask for the openat2(2) patchset (I reserved a flag bit for > it, since I'd heard about this work through the grape-vine). > I rather like the idea of having openat2 fds be non-executable by default, and having userland request it specifically via O_MAYEXEC (or some similar openat2 flag) if it's needed. Then you could add an UPGRADE_EXEC flag instead? That seems like something reasonable to do with a brand new API, and might be very helpful for preventing certain classes of attacks. -- Jeff Layton