From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Johansen Subject: Re: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs Date: Fri, 13 Jan 2012 08:27:46 +0100 Message-ID: <4F0FDCF2.6090100@canonical.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Andy Lutomirski , Will Drewry , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, serge.hallyn@canonical.com, coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com, djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org, jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com, penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, luto@mit.edu, mingo@elte.hu, akpm@linux-foundation.org, khilman@ti.com, borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com, ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de, dhowells@redhat.com, daniel.lezcano@free.fr, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, olofj@chromium.org, mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net, alan@lxorguk.ukuu.org.uk To: Kees Cook Return-path: Received: from youngberry.canonical.com ([91.189.89.112]:33187 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752151Ab2AMH16 (ORCPT ); Fri, 13 Jan 2012 02:27:58 -0500 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 01/13/2012 07:09 AM, Kees Cook wrote: > On Thu, Jan 12, 2012 at 10:02 PM, Andy Lutomirski wrote: >> On Thu, Jan 12, 2012 at 9:58 PM, Kees Cook wrote: >>> On Thu, Jan 12, 2012 at 6:12 PM, Andy Lutomirski wrote: >>>> With this set, a lot of dangerous operations (chroot, unshare, etc) >>>> become a lot less dangerous because there is no possibility of >>>> subverting privileged binaries. >>>> >>>> This patch completely breaks apparmor. Someone who understands (and >>>> uses) apparmor should fix it or at least give me a hint. >>>> >>>> Signed-off-by: Andy Lutomirski >>>> [....] >>>> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c >>>> index c1e18ba..7f480b7 100644 >>>> --- a/security/apparmor/domain.c >>>> +++ b/security/apparmor/domain.c >>>> @@ -360,6 +360,9 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm) >>>> if (bprm->cred_prepared) >>>> return 0; >>>> >>>> + /* XXX: someone who understands apparmor needs to fix this. */ >>>> + BUG_ON(bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS); >>>> + >>>> cxt = bprm->cred->security; >>>> BUG_ON(!cxt); >>>> >>> >>> Since apparmor_bprm_set_creds() calls cap_bprm_set_creds() already[1], >>> I think AppArmor needs no changes at all, but John will know better. >>> :) >> >> I think that AppArmor determines what a program is allowed to do by >> looking at the path of the executable. We don't want newly-executed >> programs to gain permissions because they're a different executable >> when we're in no_new_privs mode, so (if I'm right) something different >> needs to happen. > > I'll have to go look more closely. I thought cap_bprm_set_creds() was > already evaluating the new privs and blocking any gained privs with > the changes you were making. > We do want to do something more. A first pass at it would be to allow execs that inherit the current context, and we will also want to reject apparmor's equiv of setcon, and setexeccon, at the interface.