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=-9.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 AC1F0C2D0A7 for ; Wed, 16 Sep 2020 06:26:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E1E9221E5 for ; Wed, 16 Sep 2020 06:26:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="NwUKULRa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726133AbgIPGZ7 (ORCPT ); Wed, 16 Sep 2020 02:25:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726136AbgIPGZ4 (ORCPT ); Wed, 16 Sep 2020 02:25:56 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 164ABC06174A; Tue, 15 Sep 2020 23:25:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=5DkGrdwtKboVv6oJ+L5ofbnVJYprbMvRcR1X/5Ks8Fk=; b=NwUKULRasoHoDh5Re+0oSBPoOy cVoFabxviFAt51K/mnHZ97XXOZDkQYezTtUKQ0Ug21qeRpaVtxtxlqn+eIJOMnGZoOeLK4h1mmPe1 Yk4ICgexAbxXc56SRoycT/PX2Gm6yHY7lBVC6Sh9BEdV5Rv760gEXf7Kkkwn8Qioq0xRniiS/DEbc jSn+Ax4XAc07B3QMykBleghV6+CZPmccpDA1gI8N6d1WKCCTIZY37pK1boZ/RYKw/qD1xJX+xLGyC jEjasxT5xSri6kUplc0O7LATOQY7MvfSqKgERkQd1Re11IPDbem7jREFTAgnH5WTBSUIgqUO4x98u p114gKbQ==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIQt7-0007XL-BE; Wed, 16 Sep 2020 06:25:53 +0000 Date: Wed, 16 Sep 2020 07:25:53 +0100 From: Christoph Hellwig To: Rich Felker Cc: linux-api@vger.kernel.org, Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] vfs: block chmod of symlinks Message-ID: <20200916062553.GB27867@infradead.org> References: <20200916002157.GO3265@brightrain.aerifal.cx> <20200916002253.GP3265@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200916002253.GP3265@brightrain.aerifal.cx> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Sep 15, 2020 at 08:22:54PM -0400, Rich Felker wrote: > 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; Our usualy place for this would be setattr_prepare. Also the comment style is off, and I don't think we should talk about buggy file systems here, but a policy to not allow the chmod. I also suspect the right error value is EINVAL - EOPNOTSUPP isn't really used in normal posix file system interfaces.