From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752305AbdK1VRF (ORCPT ); Tue, 28 Nov 2017 16:17:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:37100 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751977AbdK1VRD (ORCPT ); Tue, 28 Nov 2017 16:17:03 -0500 Date: Tue, 28 Nov 2017 22:16:59 +0100 From: "Luis R. Rodriguez" To: Kees Cook Cc: "Luis R. Rodriguez" , Djalal Harouni , Andy Lutomirski , Andrew Morton , James Morris , Ben Hutchings , Solar Designer , Serge Hallyn , Jessica Yu , Rusty Russell , LKML , linux-security-module , kernel-hardening@lists.openwall.com, Jonathan Corbet , Ingo Molnar , "David S. Miller" , Network Development , Peter Zijlstra , Linus Torvalds Subject: Re: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap() Message-ID: <20171128211659.GP729@wotan.suse.de> References: <1511803118-2552-1-git-send-email-tixxdz@gmail.com> <1511803118-2552-2-git-send-email-tixxdz@gmail.com> <20171128191405.GO729@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 28, 2017 at 12:11:34PM -0800, Kees Cook wrote: > On Tue, Nov 28, 2017 at 11:14 AM, Luis R. Rodriguez wrote: > > kmod is just a helper to poke userpsace to load a module, that's it. > > > > The old init_module() and newer finit_module() do the real handy work or > > module loading, and both currently only use may_init_module(): > > > > static int may_init_module(void) > > { > > if (!capable(CAP_SYS_MODULE) || modules_disabled) > > return -EPERM; > > > > return 0; > > } > > > > This begs the question: > > > > o If userspace just tries to just use raw finit_module() do we want similar > > checks? > > > > Otherwise, correct me if I'm wrong this all seems pointless. > > Hm? That's direct-loading, not auto-loading. This series is only about > auto-loading. And *all* auto-loading uses aliases? What's the difference between auto-loading and direct-loading? > We already have a global sysctl for blocking direct-loading (modules_disabled). My point was that even if you have a CAP_NET_ADMIN check on request_module(), finit_module() will not check for it, so a crafty userspace could still try to just finit_module() directly, and completely then bypass the CAP_NET_ADMIN check. So unless I'm missing something, I see no point in adding extra checks for request_module() but nothing for the respective load_module(). Luis From mboxrd@z Thu Jan 1 00:00:00 1970 From: mcgrof@kernel.org (Luis R. Rodriguez) Date: Tue, 28 Nov 2017 22:16:59 +0100 Subject: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap() In-Reply-To: References: <1511803118-2552-1-git-send-email-tixxdz@gmail.com> <1511803118-2552-2-git-send-email-tixxdz@gmail.com> <20171128191405.GO729@wotan.suse.de> Message-ID: <20171128211659.GP729@wotan.suse.de> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org On Tue, Nov 28, 2017 at 12:11:34PM -0800, Kees Cook wrote: > On Tue, Nov 28, 2017 at 11:14 AM, Luis R. Rodriguez wrote: > > kmod is just a helper to poke userpsace to load a module, that's it. > > > > The old init_module() and newer finit_module() do the real handy work or > > module loading, and both currently only use may_init_module(): > > > > static int may_init_module(void) > > { > > if (!capable(CAP_SYS_MODULE) || modules_disabled) > > return -EPERM; > > > > return 0; > > } > > > > This begs the question: > > > > o If userspace just tries to just use raw finit_module() do we want similar > > checks? > > > > Otherwise, correct me if I'm wrong this all seems pointless. > > Hm? That's direct-loading, not auto-loading. This series is only about > auto-loading. And *all* auto-loading uses aliases? What's the difference between auto-loading and direct-loading? > We already have a global sysctl for blocking direct-loading (modules_disabled). My point was that even if you have a CAP_NET_ADMIN check on request_module(), finit_module() will not check for it, so a crafty userspace could still try to just finit_module() directly, and completely then bypass the CAP_NET_ADMIN check. So unless I'm missing something, I see no point in adding extra checks for request_module() but nothing for the respective load_module(). Luis -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 28 Nov 2017 22:16:59 +0100 From: "Luis R. Rodriguez" Message-ID: <20171128211659.GP729@wotan.suse.de> References: <1511803118-2552-1-git-send-email-tixxdz@gmail.com> <1511803118-2552-2-git-send-email-tixxdz@gmail.com> <20171128191405.GO729@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: [kernel-hardening] Re: [PATCH v5 next 1/5] modules:capabilities: add request_module_cap() To: Kees Cook Cc: "Luis R. Rodriguez" , Djalal Harouni , Andy Lutomirski , Andrew Morton , James Morris , Ben Hutchings , Solar Designer , Serge Hallyn , Jessica Yu , Rusty Russell , LKML , linux-security-module , kernel-hardening@lists.openwall.com, Jonathan Corbet , Ingo Molnar , "David S. Miller" , Network Development , Peter Zijlstra , Linus Torvalds List-ID: On Tue, Nov 28, 2017 at 12:11:34PM -0800, Kees Cook wrote: > On Tue, Nov 28, 2017 at 11:14 AM, Luis R. Rodriguez wrote: > > kmod is just a helper to poke userpsace to load a module, that's it. > > > > The old init_module() and newer finit_module() do the real handy work or > > module loading, and both currently only use may_init_module(): > > > > static int may_init_module(void) > > { > > if (!capable(CAP_SYS_MODULE) || modules_disabled) > > return -EPERM; > > > > return 0; > > } > > > > This begs the question: > > > > o If userspace just tries to just use raw finit_module() do we want similar > > checks? > > > > Otherwise, correct me if I'm wrong this all seems pointless. > > Hm? That's direct-loading, not auto-loading. This series is only about > auto-loading. And *all* auto-loading uses aliases? What's the difference between auto-loading and direct-loading? > We already have a global sysctl for blocking direct-loading (modules_disabled). My point was that even if you have a CAP_NET_ADMIN check on request_module(), finit_module() will not check for it, so a crafty userspace could still try to just finit_module() directly, and completely then bypass the CAP_NET_ADMIN check. So unless I'm missing something, I see no point in adding extra checks for request_module() but nothing for the respective load_module(). Luis