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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 39F73C2BA80 for ; Wed, 8 Apr 2020 12:21:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 182EE2083E for ; Wed, 8 Apr 2020 12:21:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728674AbgDHMVD (ORCPT ); Wed, 8 Apr 2020 08:21:03 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:49688 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728562AbgDHMVB (ORCPT ); Wed, 8 Apr 2020 08:21:01 -0400 Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jM9hR-0006C4-Vk; Wed, 08 Apr 2020 14:20:58 +0200 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 9C6DB1C0131; Wed, 8 Apr 2020 14:20:57 +0200 (CEST) Date: Wed, 08 Apr 2020 12:20:57 -0000 From: "tip-bot2 for Qian Cai" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/urgent] locking/percpu-rwsem: Fix a task_struct refcount Cc: Peter Zijlstra , Qian Cai , Ingo Molnar , x86 , LKML In-Reply-To: <20200330213002.2374-1-cai@lca.pw> References: <20200330213002.2374-1-cai@lca.pw> MIME-Version: 1.0 Message-ID: <158634845721.28353.1181972786465191647.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/urgent branch of tip: Commit-ID: d22cc7f67d55ebf2d5be865453971c783e9fb21a Gitweb: https://git.kernel.org/tip/d22cc7f67d55ebf2d5be865453971c783e9fb21a Author: Qian Cai AuthorDate: Mon, 30 Mar 2020 17:30:02 -04:00 Committer: Ingo Molnar CommitterDate: Wed, 08 Apr 2020 12:05:06 +02:00 locking/percpu-rwsem: Fix a task_struct refcount The following commit: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem") introduced task_struct memory leaks due to messing up the task_struct refcount. At the beginning of percpu_rwsem_wake_function(), it calls get_task_struct(), but if the trylock failed, it will remain in the waitqueue. However, it will run percpu_rwsem_wake_function() again with get_task_struct() to increase the refcount but then only call put_task_struct() once the trylock succeeded. Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against when percpu_rwsem_wait() observing !private, terminating the wait and doing a quick exit() while percpu_rwsem_wake_function() then doing wake_up_process(p) as a use-after-free. Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem") Suggested-by: Peter Zijlstra Signed-off-by: Qian Cai Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20200330213002.2374-1-cai@lca.pw --- kernel/locking/percpu-rwsem.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index a008a1b..8bbafe3 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int wake_flags, void *key) { - struct task_struct *p = get_task_struct(wq_entry->private); bool reader = wq_entry->flags & WQ_FLAG_CUSTOM; struct percpu_rw_semaphore *sem = key; + struct task_struct *p; /* concurrent against percpu_down_write(), can get stolen */ if (!__percpu_rwsem_trylock(sem, reader)) return 1; + p = get_task_struct(wq_entry->private); list_del_init(&wq_entry->entry); smp_store_release(&wq_entry->private, NULL);