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 7FDC5C3A5A5 for ; Thu, 5 Sep 2019 12:12:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 638DC22CF7 for ; Thu, 5 Sep 2019 12:12:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389270AbfIEMMN (ORCPT ); Thu, 5 Sep 2019 08:12:13 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:42716 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389219AbfIEMMG (ORCPT ); Thu, 5 Sep 2019 08:12:06 -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 1i5qcO-0007tc-K6; Thu, 05 Sep 2019 14:12:04 +0200 Message-Id: <20190905120540.068959005@linutronix.de> User-Agent: quilt/0.65 Date: Thu, 05 Sep 2019 14:03:44 +0200 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Frederic Weisbecker , Oleg Nesterov , Ingo Molnar , Kees Cook Subject: [patch 5/6] posix-cpu-timers: Sanitize thread clock permissions 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 thread clock permissions are restricted to tasks of the same thread group, but that also prevents a ptracer from reading them. This is inconsistent vs. the process restrictions and unnecessary strict. Relax it to ptrace permissions in the same way as process permissions are handled. Signed-off-by: Thomas Gleixner --- kernel/time/posix-cpu-timers.c | 56 +++++++++++++++++++++-------------------- 1 file changed, 29 insertions(+), 27 deletions(-) --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -51,6 +51,7 @@ void update_rlimit_cpu(struct task_struc static struct task_struct *lookup_task(const pid_t pid, bool thread, bool gettime) { + unsigned int mode = PTRACE_MODE_ATTACH_REALCREDS; struct task_struct *p; /* @@ -64,44 +65,45 @@ static struct task_struct *lookup_task(c if (!p) return p; - if (thread) - return same_thread_group(p, current) ? p : NULL; - 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. current can obviously access itself, so - * spare the ptrace check below. + * group's clock. + * + * The trivial case is that p is current or in the same + * thread group, i.e. sharing p->signal. Spare the ptrace + * check in that case. */ - if (p == current) + if (same_thread_group(p, current)) return p; - if (!thread_group_leader(p)) - return NULL; + mode = PTRACE_MODE_READ_REALCREDS; - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) - return NULL; - return p; - } + } else if (thread) { + /* + * Timer is going to be attached to a thread. If p is + * current or in the same thread group, granted. + */ + if (same_thread_group(p, current)) + return p; - /* - * For processes require that p is group leader. - */ - if (!has_group_leader_pid(p)) - return NULL; + } else { + /* + * For processes require that p is group leader. + */ + if (!has_group_leader_pid(p)) + return NULL; - /* - * Avoid the ptrace overhead when this is current's process - */ - if (same_thread_group(p, current)) - return p; + /* + * Avoid the ptrace overhead when this is current's process + */ + if (same_thread_group(p, current)) + return p; + } - /* - * Creating timers on processes which cannot be ptraced is not - * permitted: - */ - return ptrace_may_access(p, PTRACE_MODE_ATTACH_REALCREDS) ? p : NULL; + /* Decide based on the ptrace permissions. */ + return ptrace_may_access(p, mode) ? p : NULL; } static struct task_struct *__get_task_for_clock(const clockid_t clock,