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, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 656CEC3A5AB for ; Thu, 5 Sep 2019 12:12:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 426C321848 for ; Thu, 5 Sep 2019 12:12:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389295AbfIEMMY (ORCPT ); Thu, 5 Sep 2019 08:12:24 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:42705 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387775AbfIEMMF (ORCPT ); Thu, 5 Sep 2019 08:12:05 -0400 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1i5qcN-0007tE-56; Thu, 05 Sep 2019 14:12:03 +0200 Message-Id: <20190905120539.797994508@linutronix.de> User-Agent: quilt/0.65 Date: Thu, 05 Sep 2019 14:03:41 +0200 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Frederic Weisbecker , Oleg Nesterov , Ingo Molnar , Kees Cook Subject: [patch 2/6] posix-cpu-timers: Fix permission check regression References: <20190905120339.561100423@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The recent consolidation of the three permission checks introduced a subtle regression. For timer_create() with a process wide timer it returns the current task if the lookup through the PID which is encoded into the clockid results in returning current. That's broken because it does not validate whether the current task is the group leader. That was caused by the two different variants of permission checks: - posix_cpu_timer_get() allowed access to the process wide clock when the looked up task is current. That's not an issue because the process wide clock is in the shared sighand. - posix_cpu_timer_create() made sure that the looked up task is the group leader. Restore the previous state. Note, that these permission checks are more than questionable, but that's subject to follow up changes. Fixes: 6ae40e3fdcd3 ("posix-cpu-timers: Provide task validation functions") Signed-off-by: Thomas Gleixner --- kernel/time/posix-cpu-timers.c | 40 +++++++++++++++++++++++++++++++--------- 1 file changed, 31 insertions(+), 9 deletions(-) --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -47,25 +47,42 @@ void update_rlimit_cpu(struct task_struc /* * Functions for validating access to tasks. */ -static struct task_struct *lookup_task(const pid_t pid, bool thread) +static struct task_struct *lookup_task(const pid_t pid, bool thread, + bool gettime) { struct task_struct *p; + /* + * If the encoded PID is 0, then the timer is targeted at current + * or the process to which current belongs. + */ if (!pid) return thread ? current : current->group_leader; p = find_task_by_vpid(pid); - if (!p || p == current) + if (!p) return p; + if (thread) return same_thread_group(p, current) ? p : NULL; - if (p == current) - return p; + + if (gettime) { + /* + * For clock_gettime() the task does not need to be the + * actual group leader. tsk->sighand gives access to the + * group's clock. + */ + return (p == current || thread_group_leader(p)) ? p : NULL; + } + + /* + * For processes require that p is group leader. + */ return has_group_leader_pid(p) ? p : NULL; } static struct task_struct *__get_task_for_clock(const clockid_t clock, - bool getref) + bool getref, bool gettime) { const bool thread = !!CPUCLOCK_PERTHREAD(clock); const pid_t pid = CPUCLOCK_PID(clock); @@ -75,7 +92,7 @@ static struct task_struct *__get_task_fo return NULL; rcu_read_lock(); - p = lookup_task(pid, thread); + p = lookup_task(pid, thread, gettime); if (p && getref) get_task_struct(p); rcu_read_unlock(); @@ -84,12 +101,17 @@ static struct task_struct *__get_task_fo static inline struct task_struct *get_task_for_clock(const clockid_t clock) { - return __get_task_for_clock(clock, true); + return __get_task_for_clock(clock, true, false); +} + +static inline struct task_struct *get_task_for_clock_get(const clockid_t clock) +{ + return __get_task_for_clock(clock, true, true); } static inline int validate_clock_permissions(const clockid_t clock) { - return __get_task_for_clock(clock, false) ? 0 : -EINVAL; + return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL; } /* @@ -339,7 +361,7 @@ static int posix_cpu_clock_get(const clo struct task_struct *tsk; u64 t; - tsk = get_task_for_clock(clock); + tsk = get_task_for_clock_get(clock); if (!tsk) return -EINVAL;