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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 B36FDC2D0A3 for ; Mon, 2 Nov 2020 01:07:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 81AC62145D for ; Mon, 2 Nov 2020 01:07:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604279267; bh=OQvb+D7h7HOTjYq8771N7r1nGN7BKrnxLacIP8iFYPw=; h=Date:From:To:Subject:In-Reply-To:Reply-To:List-ID:From; b=XkksPRX35ZrkTClKmhF2vgkBGqsBVkqiiFl5sPpLT1gNpJwZ80PnQleptzOHDwBSl ZmkSwbj+6BQ6yWmVJY6h6PnCjz+0IEe3rycX/IhaijIYGz/hxPllFqVi9N6vSk6GRk ATMYdP/CaS5CbeNIlf4iGut09vEngIfMkEHxt4m0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727505AbgKBBHr (ORCPT ); Sun, 1 Nov 2020 20:07:47 -0500 Received: from mail.kernel.org ([198.145.29.99]:49166 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727335AbgKBBHr (ORCPT ); Sun, 1 Nov 2020 20:07:47 -0500 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7717922265; Mon, 2 Nov 2020 01:07:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604279264; bh=OQvb+D7h7HOTjYq8771N7r1nGN7BKrnxLacIP8iFYPw=; h=Date:From:To:Subject:In-Reply-To:From; b=y7lg9hA3FyhlKXd7BtKDnfpm3w0Gs6bRkEOxKvKFXFXuERcDWDEclmDzD535YwqvW 9SK4+MTxoGHbziZHKi5l6G9/JuQLFModXa0o529WR2pK9g5wG1MjzR2oXwH5E1edim Xg8kx+xsdLJ7db5rMvXX+YqIJDlUVwG9kZIheS04= Date: Sun, 01 Nov 2020 17:07:44 -0800 From: Andrew Morton To: akpm@linux-foundation.org, axboe@kernel.dk, christian@brauner.io, ebiederm@xmission.com, linux-mm@kvack.org, liuzhiqiang26@huawei.com, mm-commits@vger.kernel.org, oleg@redhat.com, stable@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org Subject: [patch 07/15] ptrace: fix task_join_group_stop() for the case when current is traced Message-ID: <20201102010744.XtB_G6WSD%akpm@linux-foundation.org> In-Reply-To: <20201101170656.48abbd5e88375219f868af5e@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Oleg Nesterov Subject: ptrace: fix task_join_group_stop() for the case when current is traced This testcase #include #include #include #include #include #include #include void *tf(void *arg) { return NULL; } int main(void) { int pid = fork(); if (!pid) { kill(getpid(), SIGSTOP); pthread_t th; pthread_create(&th, NULL, tf, NULL); return 0; } waitpid(pid, NULL, WSTOPPED); ptrace(PTRACE_SEIZE, pid, 0, PTRACE_O_TRACECLONE); waitpid(pid, NULL, 0); ptrace(PTRACE_CONT, pid, 0,0); waitpid(pid, NULL, 0); int status; int thread = waitpid(-1, &status, 0); assert(thread > 0 && thread != pid); assert(status == 0x80137f); return 0; } fails and triggers WARN_ON_ONCE(!signr) in do_jobctl_trap(). This is because task_join_group_stop() has 2 problems when current is traced: 1. We can't rely on the "JOBCTL_STOP_PENDING" check, a stopped tracee can be woken up by debugger and it can clone another thread which should join the group-stop. We need to check group_stop_count || SIGNAL_STOP_STOPPED. 2. If SIGNAL_STOP_STOPPED is already set, we should not increment sig->group_stop_count and add JOBCTL_STOP_CONSUME. The new thread should stop without another do_notify_parent_cldstop() report. To clarify, the problem is very old and we should blame ptrace_init_task(). But now that we have task_join_group_stop() it makes more sense to fix this helper to avoid the code duplication. Link: https://lkml.kernel.org/r/20201019134237.GA18810@redhat.com Signed-off-by: Oleg Nesterov Reported-by: syzbot+3485e3773f7da290eecc@syzkaller.appspotmail.com Cc: Jens Axboe Cc: Christian Brauner Cc: "Eric W . Biederman" Cc: Zhiqiang Liu Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton --- kernel/signal.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) --- a/kernel/signal.c~ptrace-fix-task_join_group_stop-for-the-case-when-current-is-traced +++ a/kernel/signal.c @@ -391,16 +391,17 @@ static bool task_participate_group_stop( void task_join_group_stop(struct task_struct *task) { + unsigned long mask = current->jobctl & JOBCTL_STOP_SIGMASK; + struct signal_struct *sig = current->signal; + + if (sig->group_stop_count) { + sig->group_stop_count++; + mask |= JOBCTL_STOP_CONSUME; + } else if (!(sig->flags & SIGNAL_STOP_STOPPED)) + return; + /* Have the new thread join an on-going signal group stop */ - unsigned long jobctl = current->jobctl; - if (jobctl & JOBCTL_STOP_PENDING) { - struct signal_struct *sig = current->signal; - unsigned long signr = jobctl & JOBCTL_STOP_SIGMASK; - unsigned long gstop = JOBCTL_STOP_PENDING | JOBCTL_STOP_CONSUME; - if (task_set_jobctl_pending(task, signr | gstop)) { - sig->group_stop_count++; - } - } + task_set_jobctl_pending(task, mask | JOBCTL_STOP_PENDING); } /* _