From patchwork Tue Nov 3 20:36:35 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 316841 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=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,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 2ADDDC388F7 for ; Tue, 3 Nov 2020 21:47:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C5B4922384 for ; Tue, 3 Nov 2020 21:46:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604440019; bh=61khsE1TzuDOx5YXSlWjxBV41HDaFppGH788FB9Bx3c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=xbOROeZtxnG4hh+PXfQ9E5E3I+hlwc5QqFQInDwcMe5eUP1fQINVolttOZUvIK1KY 97fpN6K0k7HzmhPVpldSA1giHG/JlmSJnMSwXrAH5dI6cGB0c+ye2I5jpc/8IDuBsa +jvLFTQ4Qa6tETYjvVXOk/+5vSo8dEDIMyqzpCg0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731981AbgKCUve (ORCPT ); Tue, 3 Nov 2020 15:51:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:46820 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731974AbgKCUvd (ORCPT ); Tue, 3 Nov 2020 15:51:33 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (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 0DC6E2071E; Tue, 3 Nov 2020 20:51:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604436692; bh=61khsE1TzuDOx5YXSlWjxBV41HDaFppGH788FB9Bx3c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bR0GKshO2geE/PmfyA5msqWY+4fy76SdQz8WhXNuPq7WXIIXWhuqTpgc276N33mhI KyP4mXIsD0rFde+gKW7sTNOJ0dR85LoqjULwBzFLgyUx/sYsXWQ0dRtBMfK6aVMxlV iszdFPo8ChuGgx3SyWJ9hUyDqZpiN44X6qh03FZE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, stable@kernel.org, Constantine Sapuntzakis , Jan Kara , Theodore Tso Subject: [PATCH 5.9 344/391] ext4: fix superblock checksum calculation race Date: Tue, 3 Nov 2020 21:36:35 +0100 Message-Id: <20201103203410.349940532@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203348.153465465@linuxfoundation.org> References: <20201103203348.153465465@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Constantine Sapuntzakis commit acaa532687cdc3a03757defafece9c27aa667546 upstream. The race condition could cause the persisted superblock checksum to not match the contents of the superblock, causing the superblock to be considered corrupt. An example of the race follows. A first thread is interrupted in the middle of a checksum calculation. Then, another thread changes the superblock, calculates a new checksum, and sets it. Then, the first thread resumes and sets the checksum based on the older superblock. To fix, serialize the superblock checksum calculation using the buffer header lock. While a spinlock is sufficient, the buffer header is already there and there is precedent for locking it (e.g. in ext4_commit_super). Tested the patch by booting up a kernel with the patch, creating a filesystem and some files (including some orphans), and then unmounting and remounting the file system. Cc: stable@kernel.org Signed-off-by: Constantine Sapuntzakis Reviewed-by: Jan Kara Suggested-by: Jan Kara Link: https://lore.kernel.org/r/20200914161014.22275-1-costa@purestorage.com Signed-off-by: Theodore Ts'o Signed-off-by: Greg Kroah-Hartman --- fs/ext4/super.c | 11 +++++++++++ 1 file changed, 11 insertions(+) --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -201,7 +201,18 @@ void ext4_superblock_csum_set(struct sup if (!ext4_has_metadata_csum(sb)) return; + /* + * Locking the superblock prevents the scenario + * where: + * 1) a first thread pauses during checksum calculation. + * 2) a second thread updates the superblock, recalculates + * the checksum, and updates s_checksum + * 3) the first thread resumes and finishes its checksum calculation + * and updates s_checksum with a potentially stale or torn value. + */ + lock_buffer(EXT4_SB(sb)->s_sbh); es->s_checksum = ext4_superblock_csum(sb, es); + unlock_buffer(EXT4_SB(sb)->s_sbh); } ext4_fsblk_t ext4_block_bitmap(struct super_block *sb,