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 74B56C433F5 for ; Mon, 28 Mar 2022 19:49:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344091AbiC1TvG (ORCPT ); Mon, 28 Mar 2022 15:51:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344048AbiC1TsH (ORCPT ); Mon, 28 Mar 2022 15:48:07 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3F3F569CF6; Mon, 28 Mar 2022 12:43:49 -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 29E21B81208; Mon, 28 Mar 2022 19:43:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E05FC340F0; Mon, 28 Mar 2022 19:43:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648496616; bh=w51WdM5aHvUcdwBxHUAYODPLjNrTY/mf+S4fCEB517g=; h=From:To:Cc:Subject:Date:From; b=ObydgnDh2P9VN1o1oxLU2SJl8Y1YD3RRfaASsbodum/E/Fw4iGsdq28PNTTGM6pIl TjVcivNNDcfBpyl0EO1PBJvpgNaaq/B1CnWQYoR/vMI76Ak7o3WyYZz5Hsfz7D2Cyu pUN4spJK4BEzXoblB6yldsyR01qU7Z6kgzIg8dZ1vMSqCX3PdfJIiy4YgQMnwx7ayQ BvlC66IEFCVFUOi2jizYBGpfgaQizah1SKn+d9ie/QLgbBS7lUbIZxnd2uUbrMNm9/ Y3U2qHR8BxafMK+4Uz29Ed9v2i0scwnFzrXTFxF4hRFM3DW4bLMtoiGAH7d7HsjkH1 F+Zvsr9YRoDAw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Theodore Ts'o , syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com, Lee Jones , Sasha Levin , adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org Subject: [PATCH AUTOSEL 5.4 1/2] ext4: don't BUG if someone dirty pages without asking ext4 first Date: Mon, 28 Mar 2022 15:43:32 -0400 Message-Id: <20220328194334.1586542-1-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore 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 dcbd8ac8d471..0d62f05f8925 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2161,6 +2161,15 @@ 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 @@ -2710,6 +2719,22 @@ 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