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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 9603EC64E7A for ; Tue, 1 Dec 2020 15:14:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F6962076C for ; Tue, 1 Dec 2020 15:14:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389739AbgLAPN5 (ORCPT ); Tue, 1 Dec 2020 10:13:57 -0500 Received: from lilium.sigma-star.at ([109.75.188.150]:58532 "EHLO lilium.sigma-star.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387592AbgLAPN4 (ORCPT ); Tue, 1 Dec 2020 10:13:56 -0500 Received: from localhost (localhost [127.0.0.1]) by lilium.sigma-star.at (Postfix) with ESMTP id 0F8CE18172F06; Tue, 1 Dec 2020 16:13:14 +0100 (CET) Received: from lilium.sigma-star.at ([127.0.0.1]) by localhost (lilium.sigma-star.at [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id fliEVs798DrA; Tue, 1 Dec 2020 16:13:13 +0100 (CET) Received: from lilium.sigma-star.at ([127.0.0.1]) by localhost (lilium.sigma-star.at [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id A7UHHXVABWwE; Tue, 1 Dec 2020 16:13:13 +0100 (CET) From: Richard Weinberger To: tytso@mit.edu Cc: adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Richard Weinberger Subject: [PATCH] ext4: Don't leak old mountpoint samples Date: Tue, 1 Dec 2020 16:13:01 +0100 Message-Id: <20201201151301.22025-1-richard@nod.at> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As soon the first file is opened, ext4 samples the mountpoint of the filesystem in 64 bytes of the super block. It does so using strlcpy(), this means that the remaining bytes in the super block string buffer are untouched. If the mount point before had a longer path than the current one, it can be reconstructed. Consider the case where the fs was mounted to "/media/johnjdeveloper" and later to "/". The the super block buffer then contains "/\x00edia/johnjdeveloper". This case was seen in the wild and caused confusion how the name of a developer ands up on the super block of a filesystem used in production... Fix this by clearing the string buffer before writing to it, Signed-off-by: Richard Weinberger --- fs/ext4/file.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 3ed8c048fb12..dba521250d01 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -809,6 +809,7 @@ static int ext4_sample_last_mounted(struct super_bloc= k *sb, err =3D ext4_journal_get_write_access(handle, sbi->s_sbh); if (err) goto out_journal; + memset(sbi->s_es->s_last_mounted, 0x00, sizeof(sbi->s_es->s_last_mounte= d)); strlcpy(sbi->s_es->s_last_mounted, cp, sizeof(sbi->s_es->s_last_mounted)); ext4_handle_dirty_super(handle, sb); --=20 2.26.2