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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 29B98C433DF for ; Wed, 20 May 2020 20:26:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0BB29207E8 for ; Wed, 20 May 2020 20:26:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727123AbgETU02 (ORCPT ); Wed, 20 May 2020 16:26:28 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:45686 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726827AbgETU02 (ORCPT ); Wed, 20 May 2020 16:26:28 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jbVIE-0002sC-AR; Wed, 20 May 2020 14:26:22 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jbVID-0004lz-BV; Wed, 20 May 2020 14:26:22 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Kees Cook Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Oleg Nesterov , Jann Horn , Greg Ungerer , Rob Landley , Bernd Edlinger , linux-fsdevel@vger.kernel.org, Al Viro , Alexey Dobriyan , Andrew Morton , Casey Schaufler , linux-security-module@vger.kernel.org, James Morris , "Serge E. Hallyn" , Andy Lutomirski References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org> <87v9l4zyla.fsf_-_@x220.int.ebiederm.org> <877dx822er.fsf_-_@x220.int.ebiederm.org> <87o8qkzrxp.fsf_-_@x220.int.ebiederm.org> <202005191111.9B389D33@keescook> <875zcrpx1g.fsf@x220.int.ebiederm.org> <202005191211.97BCF9DA@keescook> Date: Wed, 20 May 2020 15:22:38 -0500 In-Reply-To: <202005191211.97BCF9DA@keescook> (Kees Cook's message of "Tue, 19 May 2020 12:14:40 -0700") Message-ID: <87wo56gxv5.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jbVID-0004lz-BV;;;mid=<87wo56gxv5.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18kgvN+Xbm23VQqCP+JxcT7Yj0OsUMkK+w= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2 3/8] exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Kees Cook writes: > On Tue, May 19, 2020 at 02:03:23PM -0500, Eric W. Biederman wrote: >> Kees Cook writes: >> >> > On Mon, May 18, 2020 at 07:31:14PM -0500, Eric W. Biederman wrote: >> >> [...] >> >> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h >> >> index d1217fcdedea..8605ab4a0f89 100644 >> >> --- a/include/linux/binfmts.h >> >> +++ b/include/linux/binfmts.h >> >> @@ -27,10 +27,10 @@ struct linux_binprm { >> >> unsigned long argmin; /* rlimit marker for copy_strings() */ >> >> unsigned int >> >> /* >> >> - * True if most recent call to cap_bprm_set_creds >> >> + * True if most recent call to security_bprm_set_creds >> >> * resulted in elevated privileges. >> >> */ >> >> - cap_elevated:1, >> >> + active_secureexec:1, >> > >> > Also, I'd like it if this comment could be made more verbose as well, for >> > anyone trying to understand the binfmt execution flow for the first time. >> > Perhaps: >> > >> > /* >> > * Must be set True during the any call to >> > * bprm_set_creds hook where the execution would >> > * reuslt in elevated privileges. (The hook can be >> > * called multiple times during nested interpreter >> > * resolution across binfmt_script, binfmt_misc, etc). >> > */ >> Well it is not during but after the call that it becomes true. >> I think most recent covers the case of multiple calls. > > I'm thinking of an LSM writing reading these comments to decide what > they need to do to the flags, so it's a direction to them to set it to > true if they have determined that privilege was gained. (Though in > theory, this is all moot since only the commoncap hook cares.) The comments for an LSM writer are in include/linux/lsm_hooks.h * @bprm_repopulate_creds: * Assuming that the relevant bits of @bprm->cred->security have been * previously set, examine @bprm->file and regenerate them. This is * so that the credentials derived from the interpreter the code is * actually going to run are used rather than credentials derived * from a script. This done because the interpreter binary needs to * reopen script, and may end up opening something completely different. * This hook may also optionally check permissions (e.g. for * transitions between security domains). * The hook must set @bprm->active_secureexec to 1 if AT_SECURE should be set to * request libc enable secure mode. * @bprm contains the linux_binprm structure. * Return 0 if the hook is successful and permission is granted. I hope that is detailed enough. I will leave the rest of the comments for the maintainer of the code. I really don't think we should duplicate the prescriptive comments in multiple locations. Eric