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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 65705C43461 for ; Wed, 16 Sep 2020 00:23:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D024206A4 for ; Wed, 16 Sep 2020 00:23:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727261AbgIPAXI (ORCPT ); Tue, 15 Sep 2020 20:23:08 -0400 Received: from brightrain.aerifal.cx ([216.12.86.13]:53988 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727313AbgIPAWz (ORCPT ); Tue, 15 Sep 2020 20:22:55 -0400 Date: Tue, 15 Sep 2020 20:22:54 -0400 From: Rich Felker To: linux-api@vger.kernel.org Cc: Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/2] vfs: block chmod of symlinks Message-ID: <20200916002253.GP3265@brightrain.aerifal.cx> References: <20200916002157.GO3265@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200916002157.GO3265@brightrain.aerifal.cx> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was discovered while implementing userspace emulation of fchmodat AT_SYMLINK_NOFOLLOW (using O_PATH and procfs magic symlinks; otherwise it's not possible to target symlinks with chmod operations) that some filesystems erroneously allow access mode of symlinks to be changed, but return failure with EOPNOTSUPP (see glibc issue #14578 and commit a492b1e5ef). This inconsistency is non-conforming and wrong, and the consensus seems to be that it was unintentional to allow link modes to be changed in the first place. Signed-off-by: Rich Felker --- fs/open.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/open.c b/fs/open.c index 9af548fb841b..cdb7964aaa6e 100644 --- a/fs/open.c +++ b/fs/open.c @@ -570,6 +570,12 @@ int chmod_common(const struct path *path, umode_t mode) struct iattr newattrs; int error; + /* Block chmod from getting to fs layer. Ideally the fs would either + * allow it or fail with EOPNOTSUPP, but some are buggy and return + * an error but change the mode, which is non-conforming and wrong. */ + if (S_ISLNK(inode->i_mode)) + return -EOPNOTSUPP; + error = mnt_want_write(path->mnt); if (error) return error; -- 2.21.0