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=-18.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9F3B7C07E9A for ; Mon, 12 Jul 2021 12:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84C26610CD for ; Mon, 12 Jul 2021 12:49:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231420AbhGLMwd convert rfc822-to-8bit (ORCPT ); Mon, 12 Jul 2021 08:52:33 -0400 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:37830 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230292AbhGLMwc (ORCPT ); Mon, 12 Jul 2021 08:52:32 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-205-qiylMb6tME2iJBU66RxWTw-1; Mon, 12 Jul 2021 08:49:42 -0400 X-MC-Unique: qiylMb6tME2iJBU66RxWTw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 69A1C804319; Mon, 12 Jul 2021 12:49:39 +0000 (UTC) Received: from bahia.lan (ovpn-114-183.ams2.redhat.com [10.36.114.183]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3530961093; Mon, 12 Jul 2021 12:49:31 +0000 (UTC) Date: Mon, 12 Jul 2021 14:49:30 +0200 From: Greg Kurz To: Casey Schaufler Cc: Vivek Goyal , Christian Brauner , , , , , , , , , , Christoph Hellwig , , Subject: Re: [Virtio-fs] [PATCH v2 1/1] xattr: Allow user.* xattr on symlink and special files Message-ID: <20210712144849.121c948c@bahia.lan> In-Reply-To: <710d1c6f-d477-384f-0cc1-8914258f1fb1@schaufler-ca.com> References: <20210708175738.360757-1-vgoyal@redhat.com> <20210708175738.360757-2-vgoyal@redhat.com> <20210709091915.2bd4snyfjndexw2b@wittgenstein> <20210709152737.GA398382@redhat.com> <710d1c6f-d477-384f-0cc1-8914258f1fb1@schaufler-ca.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: On Fri, 9 Jul 2021 08:34:41 -0700 Casey Schaufler wrote: > On 7/9/2021 8:27 AM, Vivek Goyal wrote: > > On Fri, Jul 09, 2021 at 11:19:15AM +0200, Christian Brauner wrote: > >> On Thu, Jul 08, 2021 at 01:57:38PM -0400, Vivek Goyal wrote: > >>> Currently user.* xattr are not allowed on symlink and special files. > >>> > >>> man xattr and recent discussion suggested that primary reason for this > >>> restriction is how file permissions for symlinks and special files > >>> are little different from regular files and directories. > >>> > >>> For symlinks, they are world readable/writable and if user xattr were > >>> to be permitted, it will allow unpriviliged users to dump a huge amount > >>> of user.* xattrs on symlinks without any control. > >>> > >>> For special files, permissions typically control capability to read/write > >>> from devices (and not necessarily from filesystem). So if a user can > >>> write to device (/dev/null), does not necessarily mean it should be allowed > >>> to write large number of user.* xattrs on the filesystem device node is > >>> residing in. > >>> > >>> This patch proposes to relax the restrictions a bit and allow file owner > >>> or priviliged user (CAP_FOWNER), to be able to read/write user.* xattrs > >>> on symlink and special files. > >>> > >>> virtiofs daemon has a need to store user.* xatrrs on all the files > >>> (including symlinks and special files), and currently that fails. This > >>> patch should help. > >>> > >>> Link: https://lore.kernel.org/linux-fsdevel/20210625191229.1752531-1-vgoyal@redhat.com/ > >>> Signed-off-by: Vivek Goyal > >>> --- > >> Seems reasonable and useful. > >> Acked-by: Christian Brauner > >> > >> One question, do all filesystem supporting xattrs deal with setting them > >> on symlinks/device files correctly? > > Wrote a simple bash script to do setfattr/getfattr user.foo xattr on > > symlink and device node on ext4, xfs and btrfs and it works fine. > > How about nfs, tmpfs, overlayfs and/or some of the other less conventional > filesystems? > How about virtiofs then ? :-) > > > > https://github.com/rhvgoyal/misc/blob/master/generic-programs/user-xattr-special-files.sh > > > > I probably can add some more filesystems to test. > > > > Thanks > > Vivek > > > >>> fs/xattr.c | 10 ++++++---- > >>> 1 file changed, 6 insertions(+), 4 deletions(-) > >>> > >>> diff --git a/fs/xattr.c b/fs/xattr.c > >>> index 5c8c5175b385..2f1855c8b620 100644 > >>> --- a/fs/xattr.c > >>> +++ b/fs/xattr.c > >>> @@ -120,12 +120,14 @@ xattr_permission(struct user_namespace *mnt_userns, struct inode *inode, > >>> } > >>> > >>> /* > >>> - * In the user.* namespace, only regular files and directories can have > >>> - * extended attributes. For sticky directories, only the owner and > >>> - * privileged users can write attributes. > >>> + * In the user.* namespace, for symlinks and special files, only > >>> + * the owner and priviliged users can read/write attributes. > >>> + * For sticky directories, only the owner and privileged users can > >>> + * write attributes. > >>> */ > >>> if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) { > >>> - if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode)) > >>> + if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode) && > >>> + !inode_owner_or_capable(mnt_userns, inode)) > >>> return (mask & MAY_WRITE) ? -EPERM : -ENODATA; > >>> if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) && > >>> (mask & MAY_WRITE) && > >>> -- > >>> 2.25.4 > >>> > > _______________________________________________ > Virtio-fs mailing list > Virtio-fs@redhat.com > https://listman.redhat.com/mailman/listinfo/virtio-fs >