From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AEA2213B2A2 for ; Sat, 6 Jul 2024 15:32:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720279972; cv=none; b=ia2RETwTXiDfwZ0YViihauKr/IzSIETxNcZGrhoDxHhuxI+9FZtl3BB8vIVJ7EWQ230jhbLMitrsvjm2OTlNSiZuEXMxwNCOWrFjZtaoCcueWXZo3lBkr5Bx4YmngskeLmQD4x9/nip/pix4kJ5tsldbkkx/NPNDI+Ulcfc0zLo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720279972; c=relaxed/simple; bh=/7ENYiErekLpj6y4PtebCLgwC3sHbpeVxvHw0Fqh0GE=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=rnGQcSwx0hn/MkBXDz/6Hpj5rMfKPgCkoUH/jeCmu2925MEMoERTEsdZrmD1ZjucG8p500KEgZnoQLoePNm8dUi6TBV5FANfMr/6qwxWK5lh9vcDSq+W6RIX0TtcTT9vfsA6m2On3wqAUCzfcuO9hqn2yf2jlMw0FaXiQWX49TY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=cJm9s/7S; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cJm9s/7S" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1720279969; h=from:from: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; bh=oBRFKUriB/1HZETMXeJgCSmmjgsoAHSm5ov/S8Qilac=; b=cJm9s/7SBY8p/Lpv+A0c9ajsDETnymGMY0ONJ7MzScaN7cBxy4cftR6zqW6QiN5bVLtBl5 8ffUBY75+IGKnBPaIIALnmjSisRCop+Ztaymy43ke/gUrMyBbBKoTkbzvdKDRo18IlvMat /Muspkz0zgAoHJTybKW5uUuDUxhb/RE= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-281-QvlzTIlEODCCaBeRXTNIIQ-1; Sat, 06 Jul 2024 11:32:44 -0400 X-MC-Unique: QvlzTIlEODCCaBeRXTNIIQ-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BB3A8196CDEF; Sat, 6 Jul 2024 15:32:35 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.45.224.6]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AD0E819560B2; Sat, 6 Jul 2024 15:32:15 +0000 (UTC) From: Florian Weimer To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= 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 Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2) In-Reply-To: <20240706.poo9ahd3La9b@digikod.net> (=?utf-8?Q?=22Micka=C3=AB?= =?utf-8?Q?l_Sala=C3=BCn=22's?= message of "Sat, 6 Jul 2024 16:55:51 +0200") References: <20240704190137.696169-1-mic@digikod.net> <20240704190137.696169-2-mic@digikod.net> <87bk3bvhr1.fsf@oldenburg.str.redhat.com> <20240706.poo9ahd3La9b@digikod.net> Date: Sat, 06 Jul 2024 17:32:12 +0200 Message-ID: <871q46bkoz.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 * Micka=C3=ABl Sala=C3=BCn: > On Fri, Jul 05, 2024 at 08:03:14PM +0200, Florian Weimer wrote: >> * Micka=C3=ABl Sala=C3=BCn: >>=20 >> > 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 a= nd >> > 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]. >>=20 >> 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. Thanks, Florian