From patchwork Thu Jul 8 17:57:38 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vivek Goyal X-Patchwork-Id: 12365985 X-Patchwork-Delegate: paul@paul-moore.com 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=-16.4 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,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 5077BC07E96 for ; Thu, 8 Jul 2021 18:00:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F4156187E for ; Thu, 8 Jul 2021 18:00:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230130AbhGHSDI (ORCPT ); Thu, 8 Jul 2021 14:03:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:49522 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229956AbhGHSDD (ORCPT ); Thu, 8 Jul 2021 14:03:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625767221; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sNdGapRBRJZQ1Z2SOCf4wMd2iR2TD2nNsiYZrAOlxeo=; b=KRa053i4gMKqUzf/fJPG0bMHsE//jEm6YsBvzL1ctwuOsvKNNhDRCE9LkNwuWpkj/oM2n6 9NCa9spv4nKADMZbiZfHA9LpWq0l8tecLuv2x2z/3zyh54pR8OWhVWV6jXEkI2RCClMyGx H/7kRkofxByO5YGPWGHybsPel4RDYvY= 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-315-Pm6cBVeaPwyaJ5CA6J_ONg-1; Thu, 08 Jul 2021 14:00:19 -0400 X-MC-Unique: Pm6cBVeaPwyaJ5CA6J_ONg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C6BD080006E; Thu, 8 Jul 2021 18:00:17 +0000 (UTC) Received: from horse.redhat.com (ovpn-114-175.rdu2.redhat.com [10.10.114.175]) by smtp.corp.redhat.com (Postfix) with ESMTP id 38ED65D9FC; Thu, 8 Jul 2021 18:00:10 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 9FC13223D99; Thu, 8 Jul 2021 14:00:09 -0400 (EDT) From: Vivek Goyal To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk Cc: virtio-fs@redhat.com, dwalsh@redhat.com, dgilbert@redhat.com, vgoyal@redhat.com, christian.brauner@ubuntu.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 Subject: [PATCH v2 1/1] xattr: Allow user.* xattr on symlink and special files Date: Thu, 8 Jul 2021 13:57:38 -0400 Message-Id: <20210708175738.360757-2-vgoyal@redhat.com> In-Reply-To: <20210708175738.360757-1-vgoyal@redhat.com> References: <20210708175738.360757-1-vgoyal@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org 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 Acked-by: Christian Brauner --- 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) &&