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=-21.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS 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 A8B0EC07E9C for ; Fri, 9 Jul 2021 15:27:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94320611F2 for ; Fri, 9 Jul 2021 15:27:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232363AbhGIPac (ORCPT ); Fri, 9 Jul 2021 11:30:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:42090 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232288AbhGIPaa (ORCPT ); Fri, 9 Jul 2021 11:30:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625844467; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=RGgvRb7ldJO3RjHChSuXIroDn41KTYr6B2QiWafJ5SM=; b=gjIzwtvpRWlWUyHG2yMOfGneoEuqioSlCswA0naEFcaKTkDD1QdFu93dTmCh5CpTxsQBQa ACw56XlvikwazTEfWaiTsyGga696C8hkdrZh3NsDvfSxIfNk3m9du/ior80n3JWYS2G9rQ /ToKzaLok1UdntvUjavDmQNgUrsTdiI= 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-232-nwwfoorGMTe-hi9eoWaHFQ-1; Fri, 09 Jul 2021 11:27:43 -0400 X-MC-Unique: nwwfoorGMTe-hi9eoWaHFQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BF09F1842154; Fri, 9 Jul 2021 15:27:41 +0000 (UTC) Received: from horse.redhat.com (ovpn-116-62.rdu2.redhat.com [10.10.116.62]) by smtp.corp.redhat.com (Postfix) with ESMTP id 11DEA5C1A3; Fri, 9 Jul 2021 15:27:37 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 7364622054F; Fri, 9 Jul 2021 11:27:37 -0400 (EDT) Date: Fri, 9 Jul 2021 11:27:37 -0400 From: Vivek Goyal To: Christian Brauner Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, virtio-fs@redhat.com, dwalsh@redhat.com, dgilbert@redhat.com, casey.schaufler@intel.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, tytso@mit.edu, miklos@szeredi.hu, gscrivan@redhat.com, jack@suse.cz, Christoph Hellwig Subject: Re: [PATCH v2 1/1] xattr: Allow user.* xattr on symlink and special files Message-ID: <20210709152737.GA398382@redhat.com> References: <20210708175738.360757-1-vgoyal@redhat.com> <20210708175738.360757-2-vgoyal@redhat.com> <20210709091915.2bd4snyfjndexw2b@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210709091915.2bd4snyfjndexw2b@wittgenstein> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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 > > >