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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 90145C43219 for ; Wed, 16 Feb 2022 15:59:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235846AbiBPP7a (ORCPT ); Wed, 16 Feb 2022 10:59:30 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:38316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233462AbiBPP72 (ORCPT ); Wed, 16 Feb 2022 10:59:28 -0500 X-Greylist: delayed 141 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 16 Feb 2022 07:59:14 PST Received: from out03.mta.xmission.com (out03.mta.xmission.com [166.70.13.233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A3D392A39CB; Wed, 16 Feb 2022 07:59:10 -0800 (PST) Received: from in01.mta.xmission.com ([166.70.13.51]:57886) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nKMhu-009IKW-FJ; Wed, 16 Feb 2022 08:59:06 -0700 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:37452 helo=localhost.localdomain) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nKMht-002YPH-8X; Wed, 16 Feb 2022 08:59:06 -0700 From: "Eric W. Biederman" To: linux-kernel@vger.kernel.org Cc: Alexey Gladkov , Kees Cook , Shuah Khan , Christian Brauner , Solar Designer , Ran Xiaokai , containers@lists.linux-foundation.org, =?UTF-8?q?Michal=20Koutn=C3=BD?= , linux-api@vger.kernel.org, "Eric W. Biederman" , stable@vger.kernel.org Date: Wed, 16 Feb 2022 09:58:28 -0600 Message-Id: <20220216155832.680775-1-ebiederm@xmission.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <87ilteiz4a.fsf_-_@email.froward.int.ebiederm.org> References: <87ilteiz4a.fsf_-_@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-XM-SPF: eid=1nKMht-002YPH-8X;;;mid=<20220216155832.680775-1-ebiederm@xmission.com>;;;hst=in01.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19NThaI6BizHvKGbIpdTGv716FzPhyOfYM= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH v2 1/5] rlimit: Fix RLIMIT_NPROC enforcement failure caused by capability calls in set_user X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Solar Designer wrote: > I'm not aware of anyone actually running into this issue and reporting > it. The systems that I personally know use suexec along with rlimits > still run older/distro kernels, so would not yet be affected. > > So my mention was based on my understanding of how suexec works, and > code review. Specifically, Apache httpd has the setting RLimitNPROC, > which makes it set RLIMIT_NPROC: > > https://httpd.apache.org/docs/2.4/mod/core.html#rlimitnproc > > The above documentation for it includes: > > "This applies to processes forked from Apache httpd children servicing > requests, not the Apache httpd children themselves. This includes CGI > scripts and SSI exec commands, but not any processes forked from the > Apache httpd parent, such as piped logs." > > In code, there are: > > ./modules/generators/mod_cgid.c: ( (cgid_req.limits.limit_nproc_set) && ((rc = apr_procattr_limit_set(procattr, APR_LIMIT_NPROC, > ./modules/generators/mod_cgi.c: ((rc = apr_procattr_limit_set(procattr, APR_LIMIT_NPROC, > ./modules/filters/mod_ext_filter.c: rv = apr_procattr_limit_set(procattr, APR_LIMIT_NPROC, conf->limit_nproc); > > For example, in mod_cgi.c this is in run_cgi_child(). > > I think this means an httpd child sets RLIMIT_NPROC shortly before it > execs suexec, which is a SUID root program. suexec then switches to the > target user and execs the CGI script. > > Before 2863643fb8b9, the setuid() in suexec would set the flag, and the > target user's process count would be checked against RLIMIT_NPROC on > execve(). After 2863643fb8b9, the setuid() in suexec wouldn't set the > flag because setuid() is (naturally) called when the process is still > running as root (thus, has those limits bypass capabilities), and > accordingly execve() would not check the target user's process count > against RLIMIT_NPROC. In commit 2863643fb8b9 ("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds") capable calls were added to set_user to make it more consistent with fork. Unfortunately because of call site differences those capables calls were checking the credentials of the user before set*id() instead of after set*id(). This breaks enforcement of RLIMIT_NPROC for applications that set the rlimit and then call set*id() while holding a full set of capabilities. The capabilities are only changed in the new credential in security_task_fix_setuid(). The code in apache suexec appears to follow this pattern. Commit 909cc4ae86f3 ("[PATCH] Fix two bugs with process limits (RLIMIT_NPROC)") where this check was added describes the targes of this capability check as: 2/ When a root-owned process (e.g. cgiwrap) sets up process limits and then calls setuid, the setuid should fail if the user would then be running more than rlim_cur[RLIMIT_NPROC] processes, but it doesn't. This patch adds an appropriate test. With this patch, and per-user process limit imposed in cgiwrap really works. So the original use case also of this check also appears to match the broken pattern. Restore the enforcement of RLIMIT_NPROC by removing the bad capable checks added in set_user. This unfortunately restores the inconsistencies state the code has been in for the last 11 years, but dealing with the inconsistencies looks like a larger problem. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20210907213042.GA22626@openwall.com/ Link: https://lkml.kernel.org/r/20220212221412.GA29214@openwall.com Fixes: 2863643fb8b9 ("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds") History-Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git Signed-off-by: "Eric W. Biederman" --- kernel/sys.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index ecc4cf019242..8dd938a3d2bf 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -480,8 +480,7 @@ static int set_user(struct cred *new) * failure to the execve() stage. */ if (is_ucounts_overlimit(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) && - new_user != INIT_USER && - !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) + new_user != INIT_USER) current->flags |= PF_NPROC_EXCEEDED; else current->flags &= ~PF_NPROC_EXCEEDED; -- 2.29.2