From patchwork Sun Mar 8 21:38:48 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: 11425861 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 27F1613A4 for ; Sun, 8 Mar 2020 21:41:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F25842083E for ; Sun, 8 Mar 2020 21:41:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726397AbgCHVlI (ORCPT ); Sun, 8 Mar 2020 17:41:08 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:38304 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726346AbgCHVlH (ORCPT ); Sun, 8 Mar 2020 17:41:07 -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 1jB3fV-0006Qr-9X; Sun, 08 Mar 2020 15:41:05 -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 1jB3fU-0006bj-Fr; Sun, 08 Mar 2020 15:41:05 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Bernd Edlinger Cc: Christian Brauner , Kees Cook , Jann Horn , Jonathan Corbet , Alexander Viro , Andrew Morton , Alexey Dobriyan , Thomas Gleixner , Oleg Nesterov , Frederic Weisbecker , Andrei Vagin , Ingo Molnar , "Peter Zijlstra \(Intel\)" , Yuyang Du , David Hildenbrand , Sebastian Andrzej Siewior , Anshuman Khandual , David Howells , James Morris , Greg Kroah-Hartman , Shakeel Butt , Jason Gunthorpe , Christian Kellner , Andrea Arcangeli , Aleksa Sarai , "Dmitry V. Levin" , "linux-doc\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , "linux-mm\@kvack.org" , "stable\@vger.kernel.org" , "linux-api\@vger.kernel.org" References: <87k142lpfz.fsf@x220.int.ebiederm.org> <875zfmloir.fsf@x220.int.ebiederm.org> <87v9nmjulm.fsf@x220.int.ebiederm.org> <202003021531.C77EF10@keescook> <20200303085802.eqn6jbhwxtmz4j2x@wittgenstein> <87v9nlii0b.fsf@x220.int.ebiederm.org> <87a74xi4kz.fsf@x220.int.ebiederm.org> <87r1y8dqqz.fsf@x220.int.ebiederm.org> <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> Date: Sun, 08 Mar 2020 16:38:48 -0500 In-Reply-To: <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Sun, 08 Mar 2020 16:34:37 -0500") Message-ID: <87zhcq4jdj.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=1jB3fU-0006bj-Fr;;;mid=<87zhcq4jdj.fsf_-_@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18BoLeVKTmhJXInoxrgoo4cUvE+MboM0ho= 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 sa08.xmission.com X-Spam-Level: * X-Spam-Status: No, score=1.7 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,LotsOfNums_01,T_TM2_M_HEADER_IN_MSG,T_TooManySym_01, XMSubLong autolearn=disabled version=3.4.2 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] * 0.7 XMSubLong Long Subject * 1.2 LotsOfNums_01 BODY: Lots of long strings of numbers * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa08 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa08 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: *;Bernd Edlinger X-Spam-Relay-Country: X-Spam-Timing: total 396 ms - load_scoreonly_sql: 0.04 (0.0%), signal_user_changed: 3.9 (1.0%), b_tie_ro: 2.8 (0.7%), parse: 1.07 (0.3%), extract_message_metadata: 11 (2.8%), get_uri_detail_list: 2.6 (0.7%), tests_pri_-1000: 16 (4.0%), tests_pri_-950: 1.64 (0.4%), tests_pri_-900: 1.22 (0.3%), tests_pri_-90: 41 (10.3%), check_bayes: 39 (9.9%), b_tokenize: 14 (3.5%), b_tok_get_all: 12 (3.0%), b_comp_prob: 3.1 (0.8%), b_tok_touch_all: 6 (1.6%), b_finish: 0.87 (0.2%), tests_pri_0: 308 (77.8%), check_dkim_signature: 0.55 (0.1%), check_dkim_adsp: 2.6 (0.7%), poll_dns_idle: 0.93 (0.2%), tests_pri_10: 2.2 (0.6%), tests_pri_500: 7 (1.8%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex 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 The cred_guard_mutex is problematic. The cred_guard_mutex is held over the userspace accesses as the arguments from userspace are read. The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other threads are killed. The cred_guard_mutex is held over "put_user(0, tsk->clear_child_tid)" in exit_mm(). Any of those can result in deadlock, as the cred_guard_mutex is held over a possible indefinite userspace waits for userspace. Add exec_update_mutex that is only held over exec updating process with the new contents of exec, so that code that needs not to be confused by exec changing the mm and the cred in ways that can not happen during ordinary execution of a process. The plan is to switch the users of cred_guard_mutex to exec_udpate_mutex one by one. This lets us move forward while still being careful and not introducing any regressions. Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/ Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/ Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/ Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/ Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/ Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") Signed-off-by: "Eric W. Biederman" Reviewed-by: Bernd Edlinger Reviewed-by: Kees Cook Signed-off-by: Bernd Edlinger Reviewed-by: Kirill Tkhai --- fs/exec.c | 9 +++++++++ include/linux/sched/signal.h | 9 ++++++++- init/init_task.c | 1 + kernel/fork.c | 1 + 4 files changed, 19 insertions(+), 1 deletion(-) diff --git a/fs/exec.c b/fs/exec.c index d820a7272a76..ffeebb1f167b 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1014,6 +1014,7 @@ static int exec_mmap(struct mm_struct *mm) { struct task_struct *tsk; struct mm_struct *old_mm, *active_mm; + int ret; /* Notify parent that we're no longer interested in the old VM */ tsk = current; @@ -1034,6 +1035,11 @@ static int exec_mmap(struct mm_struct *mm) return -EINTR; } } + + ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); + if (ret) + return ret; + task_lock(tsk); active_mm = tsk->active_mm; membarrier_exec_mmap(mm); @@ -1438,6 +1444,8 @@ static void free_bprm(struct linux_binprm *bprm) { free_arg_pages(bprm); if (bprm->cred) { + if (!bprm->mm) + mutex_unlock(¤t->signal->exec_update_mutex); mutex_unlock(¤t->signal->cred_guard_mutex); abort_creds(bprm->cred); } @@ -1487,6 +1495,7 @@ void install_exec_creds(struct linux_binprm *bprm) * credentials; any time after this it may be unlocked. */ security_bprm_committed_creds(bprm); + mutex_unlock(¤t->signal->exec_update_mutex); mutex_unlock(¤t->signal->cred_guard_mutex); } EXPORT_SYMBOL(install_exec_creds); diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 88050259c466..a29df79540ce 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -224,7 +224,14 @@ struct signal_struct { struct mutex cred_guard_mutex; /* guard against foreign influences on * credential calculations - * (notably. ptrace) */ + * (notably. ptrace) + * Deprecated do not use in new code. + * Use exec_update_mutex instead. + */ + struct mutex exec_update_mutex; /* Held while task_struct is being + * updated during exec, and may have + * inconsistent permissions. + */ } __randomize_layout; /* diff --git a/init/init_task.c b/init/init_task.c index 9e5cbe5eab7b..bd403ed3e418 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -26,6 +26,7 @@ static struct signal_struct init_signals = { .multiprocess = HLIST_HEAD_INIT, .rlim = INIT_RLIMITS, .cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex), + .exec_update_mutex = __MUTEX_INITIALIZER(init_signals.exec_update_mutex), #ifdef CONFIG_POSIX_TIMERS .posix_timers = LIST_HEAD_INIT(init_signals.posix_timers), .cputimer = { diff --git a/kernel/fork.c b/kernel/fork.c index 60a1295f4384..12896a6ecee6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1594,6 +1594,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) sig->oom_score_adj_min = current->signal->oom_score_adj_min; mutex_init(&sig->cred_guard_mutex); + mutex_init(&sig->exec_update_mutex); return 0; }