From patchwork Thu May 28 15:50:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 11576253 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0B08313B4 for ; Thu, 28 May 2020 15:54:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0CF82053B for ; Thu, 28 May 2020 15:54:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404749AbgE1PyI (ORCPT ); Thu, 28 May 2020 11:54:08 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:53032 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404511AbgE1PyD (ORCPT ); Thu, 28 May 2020 11:54:03 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jeKr3-0005Lz-CC; Thu, 28 May 2020 09:54:01 -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 1jeKr2-0003Dg-EH; Thu, 28 May 2020 09:54:01 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Cc: Linus Torvalds , Oleg Nesterov , Jann Horn , Kees Cook , Greg Ungerer , Rob Landley , Bernd Edlinger , , 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> <87k10wysqz.fsf_-_@x220.int.ebiederm.org> Date: Thu, 28 May 2020 10:50:09 -0500 In-Reply-To: <87k10wysqz.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Thu, 28 May 2020 10:38:28 -0500") Message-ID: <87sgfkvz2m.fsf_-_@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1jeKr2-0003Dg-EH;;;mid=<87sgfkvz2m.fsf_-_@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+noWZXFqvq+oA4X8eGsRDwP21udiMjpIw= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa02.xmission.com X-Spam-Level: ** X-Spam-Status: No, score=2.0 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,T_TooManySym_01,XMNoVowels,XMSubLong autolearn=disabled version=3.4.2 X-Spam-Virus: No X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.7 XMSubLong Long Subject * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa02 0; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: ; sa02 0; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **; X-Spam-Relay-Country: X-Spam-Timing: total 530 ms - load_scoreonly_sql: 0.03 (0.0%), signal_user_changed: 4.4 (0.8%), b_tie_ro: 3.0 (0.6%), parse: 1.09 (0.2%), extract_message_metadata: 12 (2.2%), get_uri_detail_list: 1.92 (0.4%), tests_pri_-1000: 11 (2.1%), tests_pri_-950: 1.14 (0.2%), tests_pri_-900: 0.85 (0.2%), tests_pri_-90: 229 (43.1%), check_bayes: 227 (42.8%), b_tokenize: 7 (1.3%), b_tok_get_all: 7 (1.2%), b_comp_prob: 1.73 (0.3%), b_tok_touch_all: 209 (39.4%), b_finish: 0.83 (0.2%), tests_pri_0: 262 (49.3%), check_dkim_signature: 0.59 (0.1%), check_dkim_adsp: 2.1 (0.4%), poll_dns_idle: 0.80 (0.2%), tests_pri_10: 1.80 (0.3%), tests_pri_500: 6 (1.0%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH 10/11] exec: In bprm_fill_uid set secureexec at same time as per_clear X-Spam-Flag: No 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 We currently have two different policies for setting per_clear and for setting secureexec. For per_clear the policy is if the setxid bits on a file are honored. For secureexec the policy is if the resulting credentials will have multiple uids or gids. Looking closely the policy for setting AT_SECURE and asking userspace not to trust our caller in all cases where we have multiple uids or gids does not make sense. In some of those cases it is the caller of exec that provides multiple uids and gids. The point of setting AT_SECURE is so that the called application or it's libraries can take defensive measures to guard against a lesser privileged program which calls it via exec. If all of your privilege comes from your caller there is no point in taking defensive measures, against them. Further the only way that libc or other userspace can know that the privilege came from the caller of exec and not from the exec being suid or sgid is by the kernel telling it. As userspace does not have enough information to distinguish between these two cases. So set secureexec when the exec itself results in multiple uids or gids, not when we happen to have mulitple ids because the binary was called that way. Signed-off-by: "Eric W. Biederman" --- fs/exec.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 347dade4bc54..fc4edc7517a6 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1637,19 +1637,19 @@ static void bprm_fill_uid(struct linux_binprm *bprm) if ((mode & S_ISUID) && (!need_cap || ns_capable(new->user_ns, CAP_SETUID))) { bprm->per_clear = 1; + bprm->secureexec = 1; new->suid = new->fsuid = new->euid = uid; } if (((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) && (!need_cap || ns_capable(new->user_ns, CAP_SETGID))) { bprm->per_clear = 1; + bprm->secureexec = 1; new->sgid = new->fsgid = new->egid = gid; } after_setid: - /* Will the new creds have multiple uids or gids? */ - if (!uid_eq(new->euid, new->uid) || !gid_eq(new->egid, new->gid)) - bprm->secureexec = 1; + ; } /*