From patchwork Mon Jan 4 15:57:43 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 356755 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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 DF4D0C433DB for ; Mon, 4 Jan 2021 16:06:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB0A1207AE for ; Mon, 4 Jan 2021 16:06:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728962AbhADQC6 (ORCPT ); Mon, 4 Jan 2021 11:02:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:39992 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728954AbhADQC6 (ORCPT ); Mon, 4 Jan 2021 11:02:58 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 17B6F20769; Mon, 4 Jan 2021 16:02:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609776162; bh=NqEGqp1novZlMhQPthLuK9lzcA9lKdPOjw64y0wArsg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nUJ3zA2P3GwrrGuBkJCdQj5UtGARi/iwnd547bSN9yv/emb4341UsmAEUG5x4DP3p 4UOztkuwLuB0zoVyGAnrmMrXTLiRuv+Qx3r22q0PqLjYZo1J88sGQtXwl0Jd9dNGrz kJGkbRt2qTPS1QqlCz8NxhPXsctYjYlTnN37rAMk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Miklos Szeredi , Eric Biggers , Al Viro , Sasha Levin Subject: [PATCH 5.10 50/63] fs/namespace.c: WARN if mnt_count has become negative Date: Mon, 4 Jan 2021 16:57:43 +0100 Message-Id: <20210104155711.239399679@linuxfoundation.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210104155708.800470590@linuxfoundation.org> References: <20210104155708.800470590@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Biggers [ Upstream commit edf7ddbf1c5eb98b720b063b73e20e8a4a1ce673 ] Missing calls to mntget() (or equivalently, too many calls to mntput()) are hard to detect because mntput() delays freeing mounts using task_work_add(), then again using call_rcu(). As a result, mnt_count can often be decremented to -1 without getting a KASAN use-after-free report. Such cases are still bugs though, and they point to real use-after-frees being possible. For an example of this, see the bug fixed by commit 1b0b9cc8d379 ("vfs: fsmount: add missing mntget()"), discussed at https://lkml.kernel.org/linux-fsdevel/20190605135401.GB30925@xxxxxxxxxxxxxxxxxxxxxxxxx/T/#u. This bug *should* have been trivial to find. But actually, it wasn't found until syzkaller happened to use fchdir() to manipulate the reference count just right for the bug to be noticeable. Address this by making mntput_no_expire() issue a WARN if mnt_count has become negative. Suggested-by: Miklos Szeredi Signed-off-by: Eric Biggers Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/namespace.c | 9 ++++++--- fs/pnode.h | 2 +- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index cebaa3e817940..93006abe7946a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -156,10 +156,10 @@ static inline void mnt_add_count(struct mount *mnt, int n) /* * vfsmount lock must be held for write */ -unsigned int mnt_get_count(struct mount *mnt) +int mnt_get_count(struct mount *mnt) { #ifdef CONFIG_SMP - unsigned int count = 0; + int count = 0; int cpu; for_each_possible_cpu(cpu) { @@ -1139,6 +1139,7 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput); static void mntput_no_expire(struct mount *mnt) { LIST_HEAD(list); + int count; rcu_read_lock(); if (likely(READ_ONCE(mnt->mnt_ns))) { @@ -1162,7 +1163,9 @@ static void mntput_no_expire(struct mount *mnt) */ smp_mb(); mnt_add_count(mnt, -1); - if (mnt_get_count(mnt)) { + count = mnt_get_count(mnt); + if (count != 0) { + WARN_ON(count < 0); rcu_read_unlock(); unlock_mount_hash(); return; diff --git a/fs/pnode.h b/fs/pnode.h index 49a058c73e4c7..26f74e092bd98 100644 --- a/fs/pnode.h +++ b/fs/pnode.h @@ -44,7 +44,7 @@ int propagate_mount_busy(struct mount *, int); void propagate_mount_unlock(struct mount *); void mnt_release_group_id(struct mount *); int get_dominating_id(struct mount *mnt, const struct path *root); -unsigned int mnt_get_count(struct mount *mnt); +int mnt_get_count(struct mount *mnt); void mnt_set_mountpoint(struct mount *, struct mountpoint *, struct mount *); void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp,