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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 BA14EC4360C for ; Sun, 6 Oct 2019 17:19:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 92FFF20862 for ; Sun, 6 Oct 2019 17:19:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570382397; bh=2DCA2JJBF8fHFC/ZMKUaa+G7x7G8mapNrW+n9g2fff0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=r2tXbOVgZB76RGk4m8CIrOA8iIAiqOlstCuUSrjXYyTNVYv1fatXNGV2a+gaeETvV 4mTEpqLD8aO82s/LC1YsdbpmQKuzbv8X7VWT0zNGit7EvkeFg6gkjHBL+mwKgpHmZ/ CsOTSstsQWwqgn0zZPtgChF9MCNhwyuitENPl9AM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727046AbfJFRT4 (ORCPT ); Sun, 6 Oct 2019 13:19:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:44850 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726992AbfJFRTx (ORCPT ); Sun, 6 Oct 2019 13:19:53 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 29F0820862; Sun, 6 Oct 2019 17:19:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570382392; bh=2DCA2JJBF8fHFC/ZMKUaa+G7x7G8mapNrW+n9g2fff0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z9UFnqJ75fbaSmoinlGKKSpxeYVmnV2Y9wWoTJrm/ZcelXkqDfPrXadoJAHDM7cUa xRF2yZd/PIddGAg1Ke8MdM85OAKioV14ubIJ92SrCAWHjrnM/NGEC99w0LxujVDIFF WO80TBesIYUklNLxxGDCR7AYdEjfD2y08eCsXbIA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, OGAWA Hirofumi , Jan Stancek , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.4 19/36] fat: work around race with userspaces read via blockdev while mounting Date: Sun, 6 Oct 2019 19:19:01 +0200 Message-Id: <20191006171052.994560902@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191006171038.266461022@linuxfoundation.org> References: <20191006171038.266461022@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: OGAWA Hirofumi [ Upstream commit 07bfa4415ab607e459b69bd86aa7e7602ce10b4f ] If userspace reads the buffer via blockdev while mounting, sb_getblk()+modify can race with buffer read via blockdev. For example, FS userspace bh = sb_getblk() modify bh->b_data read ll_rw_block(bh) fill bh->b_data by on-disk data /* lost modified data by FS */ set_buffer_uptodate(bh) set_buffer_uptodate(bh) Userspace should not use the blockdev while mounting though, the udev seems to be already doing this. Although I think the udev should try to avoid this, workaround the race by small overhead. Link: http://lkml.kernel.org/r/87pnk7l3sw.fsf_-_@mail.parknet.co.jp Signed-off-by: OGAWA Hirofumi Reported-by: Jan Stancek Tested-by: Jan Stancek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- fs/fat/dir.c | 13 +++++++++++-- fs/fat/fatent.c | 3 +++ 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/fs/fat/dir.c b/fs/fat/dir.c index 8b2127ffb226c..9b77e2ad2b597 100644 --- a/fs/fat/dir.c +++ b/fs/fat/dir.c @@ -1097,8 +1097,11 @@ static int fat_zeroed_cluster(struct inode *dir, sector_t blknr, int nr_used, err = -ENOMEM; goto error; } + /* Avoid race with userspace read via bdev */ + lock_buffer(bhs[n]); memset(bhs[n]->b_data, 0, sb->s_blocksize); set_buffer_uptodate(bhs[n]); + unlock_buffer(bhs[n]); mark_buffer_dirty_inode(bhs[n], dir); n++; @@ -1155,6 +1158,8 @@ int fat_alloc_new_dir(struct inode *dir, struct timespec *ts) fat_time_unix2fat(sbi, ts, &time, &date, &time_cs); de = (struct msdos_dir_entry *)bhs[0]->b_data; + /* Avoid race with userspace read via bdev */ + lock_buffer(bhs[0]); /* filling the new directory slots ("." and ".." entries) */ memcpy(de[0].name, MSDOS_DOT, MSDOS_NAME); memcpy(de[1].name, MSDOS_DOTDOT, MSDOS_NAME); @@ -1177,6 +1182,7 @@ int fat_alloc_new_dir(struct inode *dir, struct timespec *ts) de[0].size = de[1].size = 0; memset(de + 2, 0, sb->s_blocksize - 2 * sizeof(*de)); set_buffer_uptodate(bhs[0]); + unlock_buffer(bhs[0]); mark_buffer_dirty_inode(bhs[0], dir); err = fat_zeroed_cluster(dir, blknr, 1, bhs, MAX_BUF_PER_PAGE); @@ -1234,11 +1240,14 @@ static int fat_add_new_entries(struct inode *dir, void *slots, int nr_slots, /* fill the directory entry */ copy = min(size, sb->s_blocksize); + /* Avoid race with userspace read via bdev */ + lock_buffer(bhs[n]); memcpy(bhs[n]->b_data, slots, copy); - slots += copy; - size -= copy; set_buffer_uptodate(bhs[n]); + unlock_buffer(bhs[n]); mark_buffer_dirty_inode(bhs[n], dir); + slots += copy; + size -= copy; if (!size) break; n++; diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c index e3fc477728b32..be8529739d23e 100644 --- a/fs/fat/fatent.c +++ b/fs/fat/fatent.c @@ -389,8 +389,11 @@ static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs, err = -ENOMEM; goto error; } + /* Avoid race with userspace read via bdev */ + lock_buffer(c_bh); memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize); set_buffer_uptodate(c_bh); + unlock_buffer(c_bh); mark_buffer_dirty_inode(c_bh, sbi->fat_inode); if (sb->s_flags & MS_SYNCHRONOUS) err = sync_dirty_buffer(c_bh); -- 2.20.1