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=-1.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, LONGWORDS,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 E7D9CC433E2 for ; Wed, 20 May 2020 14:29:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D05B4205CB for ; Wed, 20 May 2020 14:29:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726819AbgETOWV (ORCPT ); Wed, 20 May 2020 10:22:21 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60900 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726443AbgETOWU (ORCPT ); Wed, 20 May 2020 10:22:20 -0400 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1jbPbu-00034u-5G; Wed, 20 May 2020 15:22:18 +0100 Received: from ben by deadeye with local (Exim 4.93) (envelope-from ) id 1jbPbt-007DNv-Mk; Wed, 20 May 2020 15:22:17 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Piotr Krysiuk" , "Al Viro" , "Greg Kroah-Hartman" Date: Wed, 20 May 2020 15:13:29 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 01/99] fs/namespace.c: fix mountpoint reference counter race In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.84-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Piotr Krysiuk A race condition between threads updating mountpoint reference counter affects longterm releases 4.4.220, 4.9.220, 4.14.177 and 4.19.118. The mountpoint reference counter corruption may occur when: * one thread increments m_count member of struct mountpoint [under namespace_sem, but not holding mount_lock] pivot_root() * another thread simultaneously decrements the same m_count [under mount_lock, but not holding namespace_sem] put_mountpoint() unhash_mnt() umount_mnt() mntput_no_expire() To fix this race condition, grab mount_lock before updating m_count in pivot_root(). Reference: CVE-2020-12114 Cc: Al Viro Signed-off-by: Piotr Krysiuk Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- fs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2937,8 +2937,8 @@ SYSCALL_DEFINE2(pivot_root, const char _ /* make certain new is below the root */ if (!is_path_reachable(new_mnt, new.dentry, &root)) goto out4; - root_mp->m_count++; /* pin it so it won't go away */ lock_mount_hash(); + root_mp->m_count++; /* pin it so it won't go away */ detach_mnt(new_mnt, &parent_path); detach_mnt(root_mnt, &root_parent); if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {