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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 895B3C433F5 for ; Tue, 5 Apr 2022 13:41:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1390411AbiDENic (ORCPT ); Tue, 5 Apr 2022 09:38:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344346AbiDEJTd (ORCPT ); Tue, 5 Apr 2022 05:19:33 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2D11B23BF7; Tue, 5 Apr 2022 02:07:32 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D020FB81C15; Tue, 5 Apr 2022 09:07:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 232D8C385A0; Tue, 5 Apr 2022 09:07:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649149649; bh=fHWOggZ0S4hvTFd4G0AD1ngfqFQeOt9QOGZoZs+G7so=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=L9UC9+ovCVrEFQzEwZSAZ8shiW2mUTqOkKJU0NvALIOLkCXLxCmxGQ9X69PjgWJCR sNBlayIKPL6r/LthYf4NgUTbSORWeKdYcYQ3/sYaBS9Y4gGtR0FcwjsUvZW/ugYZIN 9QHv22gxDWwQTC0Rbc4KBTZFYyDbcoOBzRsGtP9Q= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com, Lee Jones , Theodore Tso , Sasha Levin Subject: [PATCH 5.16 0790/1017] ext4: dont BUG if someone dirty pages without asking ext4 first Date: Tue, 5 Apr 2022 09:28:23 +0200 Message-Id: <20220405070417.703356282@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220405070354.155796697@linuxfoundation.org> References: <20220405070354.155796697@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Theodore Ts'o [ Upstream commit cc5095747edfb054ca2068d01af20be3fcc3634f ] [un]pin_user_pages_remote is dirtying pages without properly warning the file system in advance. A related race was noted by Jan Kara in 2018[1]; however, more recently instead of it being a very hard-to-hit race, it could be reliably triggered by process_vm_writev(2) which was discovered by Syzbot[2]. This is technically a bug in mm/gup.c, but arguably ext4 is fragile in that if some other kernel subsystem dirty pages without properly notifying the file system using page_mkwrite(), ext4 will BUG, while other file systems will not BUG (although data will still be lost). So instead of crashing with a BUG, issue a warning (since there may be potential data loss) and just mark the page as clean to avoid unprivileged denial of service attacks until the problem can be properly fixed. More discussion and background can be found in the thread starting at [2]. [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz [2] https://lore.kernel.org/r/Yg0m6IjcNmfaSokM@google.com Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com Reported-by: Lee Jones Signed-off-by: Theodore Ts'o Link: https://lore.kernel.org/r/YiDS9wVfq4mM2jGK@mit.edu Signed-off-by: Sasha Levin --- fs/ext4/inode.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 2f5686dfa30d..a61d1e4e1026 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1992,6 +1992,15 @@ static int ext4_writepage(struct page *page, else len = PAGE_SIZE; + /* Should never happen but for bugs in other kernel subsystems */ + if (!page_has_buffers(page)) { + ext4_warning_inode(inode, + "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + return 0; + } + page_bufs = page_buffers(page); /* * We cannot do block allocation or other extent handling in this @@ -2595,6 +2604,22 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) wait_on_page_writeback(page); BUG_ON(PageWriteback(page)); + /* + * Should never happen but for buggy code in + * other subsystems that call + * set_page_dirty() without properly warning + * the file system first. See [1] for more + * information. + * + * [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz + */ + if (!page_has_buffers(page)) { + ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + continue; + } + if (mpd->map.m_len == 0) mpd->first_page = page->index; mpd->next_page = page->index + 1; -- 2.34.1