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 91C3CC433EF for ; Fri, 11 Feb 2022 19:57:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353026AbiBKT5D (ORCPT ); Fri, 11 Feb 2022 14:57:03 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:36752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235284AbiBKT5C (ORCPT ); Fri, 11 Feb 2022 14:57:02 -0500 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD40632D for ; Fri, 11 Feb 2022 11:57:00 -0800 (PST) Received: from in02.mta.xmission.com ([166.70.13.52]:52364) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nIc2M-002ugY-Bt; Fri, 11 Feb 2022 12:56:58 -0700 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:51124 helo=email.froward.int.ebiederm.org.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nIc2J-00A0GN-BV; Fri, 11 Feb 2022 12:56:57 -0700 From: "Eric W. Biederman" To: Alexey Gladkov Cc: linux-kernel@vger.kernel.org, Kees Cook , Shuah Khan , Christian Brauner , Solar Designer , Ran Xiaokai , containers@lists.linux.dev, Michal =?utf-8?Q?Koutn=C3=BD?= References: <87o83e2mbu.fsf@email.froward.int.ebiederm.org> <20220211021324.4116773-6-ebiederm@xmission.com> <20220211113454.socmlrne5heux7q7@example.org> <87sfspz409.fsf@email.froward.int.ebiederm.org> <20220211184041.dlqjk2fgdnkmtpe3@example.org> Date: Fri, 11 Feb 2022 13:56:29 -0600 In-Reply-To: <20220211184041.dlqjk2fgdnkmtpe3@example.org> (Alexey Gladkov's message of "Fri, 11 Feb 2022 19:40:41 +0100") Message-ID: <87zgmxxjma.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1nIc2J-00A0GN-BV;;;mid=<87zgmxxjma.fsf@email.froward.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19E7a/eaKFtZzvaoEdxpINrDSEu8ypYCyc= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 6/8] ucounts: Handle inc_rlimit_ucounts wrapping in fork X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexey Gladkov writes: > On Fri, Feb 11, 2022 at 11:50:46AM -0600, Eric W. Biederman wrote: >> Alexey Gladkov writes: >> >> > On Thu, Feb 10, 2022 at 08:13:22PM -0600, Eric W. Biederman wrote: >> >> Move inc_rlimit_ucounts from copy_creds into copy_process immediately >> >> after copy_creds where it can be called exactly once. Test for and >> >> handle it when inc_rlimit_ucounts returns LONG_MAX indicating the >> >> count has wrapped. >> >> >> >> This is good hygenine and fixes a theoretical bug. In practice >> >> PID_MAX_LIMIT is at most 2^22 so there is not a chance the number of >> >> processes would ever wrap even on an architecture with a 32bit long. >> >> >> >> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") >> >> Signed-off-by: "Eric W. Biederman" >> >> --- >> >> kernel/cred.c | 2 -- >> >> kernel/fork.c | 2 ++ >> >> 2 files changed, 2 insertions(+), 2 deletions(-) >> >> >> >> diff --git a/kernel/cred.c b/kernel/cred.c >> >> index 229cff081167..96d5fd6ff26f 100644 >> >> --- a/kernel/cred.c >> >> +++ b/kernel/cred.c >> >> @@ -358,7 +358,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >> >> kdebug("share_creds(%p{%d,%d})", >> >> p->cred, atomic_read(&p->cred->usage), >> >> read_cred_subscribers(p->cred)); >> >> - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >> >> return 0; >> >> } >> >> >> >> @@ -395,7 +394,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) >> >> #endif >> >> >> >> p->cred = p->real_cred = get_cred(new); >> >> - inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1); >> >> alter_cred_subscribers(new, 2); >> >> validate_creds(new); >> >> return 0; >> >> diff --git a/kernel/fork.c b/kernel/fork.c >> >> index 6f62d37f3650..69333078259c 100644 >> >> --- a/kernel/fork.c >> >> +++ b/kernel/fork.c >> >> @@ -2026,6 +2026,8 @@ static __latent_entropy struct task_struct *copy_process( >> >> goto bad_fork_free; >> >> >> >> retval = -EAGAIN; >> >> + if (inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1) == LONG_MAX) >> >> + goto bad_fork_cleanup_count; >> >> if (is_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) { >> >> if ((task_ucounts(p) != &init_ucounts) && >> >> !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) >> > >> > It might make sense to do something like: >> > >> > if (inc_rlimit_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1, rlimit(RLIMIT_NPROC)) == LONG_MAX) { >> > if ((task_ucounts(p) != &init_ucounts) && >> > !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) >> > >> > and the new function: >> > >> > long inc_rlimit_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, long v, unsigned long rlimit) >> > { >> > struct ucounts *iter; >> > long ret = 0; >> > long max = rlimit; >> > if (rlimit > LONG_MAX) >> > max = LONG_MAX; >> > for (iter = ucounts; iter; iter = iter->ns->ucounts) { >> > long new = atomic_long_add_return(v, &iter->ucount[type]); >> > if (new < 0 || new > max) >> > ret = LONG_MAX; >> > else if (iter == ucounts) >> > ret = new; >> > max = READ_ONCE(iter->ns->ucount_max[type]); >> > } >> > return ret; >> > } >> > >> > This will avoid double checking the same userns tree. >> > >> > Or even modify inc_rlimit_ucounts. This function is used elsewhere like >> > this: >> > >> > >> > msgqueue = inc_rlimit_ucounts(info->ucounts, UCOUNT_RLIMIT_MSGQUEUE, mq_bytes); >> > if (msgqueue == LONG_MAX || msgqueue > rlimit(RLIMIT_MSGQUEUE)) { >> > >> > >> > memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); >> > if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) { >> > >> > >> > In all cases, we have max value for comparison. >> >> Good point. The downside is that it means we can't use the same code >> in exec. The upside is that the code is more idiomatic. > > My suggestion was before I saw the 8/8 patch :) > > We can make something like: > > static inline bool is_nproc_overlimit(struct task_struct *task) > { > return (task_ucounts(task) != &init_ucounts) && > !has_capability(task, CAP_SYS_RESOURCE) && > !has_capability(task, CAP_SYS_ADMIN); > } > > In copy_process: > > if (inc_rlimit_ucounts_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1, rlimit(RLIMIT_NPROC)) == LONG_MAX) { > if (is_nproc_overlimit(p)) > goto bad_fork_cleanup_count; > } > > In do_execveat_common: > > if ((current->flags & PF_NPROC_CHECK) && > is_ucounts_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) && > is_nproc_overlimit(current)) { > retval = -EAGAIN; > goto out_ret; > } The more I think about it the more I suspect 8/8 is the wrong way to go. The report is that adding the capability calls in kernel/sys.c which I moved into execve broke apache. As the change was about removing inconsistencies I expect I should just start with the revert and keep the difference between the two code paths. My gut feel is that both the capable and the magic exception of a user are wrong. If I am wrong people can report a bug and the code can get fixed. But definitely a bug fix branch is the wrong place to be expanding what is allowed without it clearly being a bug. Eric