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=-15.8 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 58C8BC43381 for ; Mon, 1 Mar 2021 18:10:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22F98651C1 for ; Mon, 1 Mar 2021 18:10:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238587AbhCASJs (ORCPT ); Mon, 1 Mar 2021 13:09:48 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:24686 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234470AbhCAQfU (ORCPT ); Mon, 1 Mar 2021 11:35:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614616416; 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=NXTK4ZGu5+ooGvAa6Xkt4bycI9XBagy87L8rBkPbpi0=; b=bjTm1iIR41eLLkpiqibx2W1a6vgCpCfbVTnT1shKaRTuUI/tqlhaXr+m9VCzzg7CUdD5CT Ng1o8vTif+BxNp7ANidI3GGW2ZhghVsHh++byS+6JkRtxNxAUJWROX+eVathtlYyV0oqK0 xUSq9ZmVQ5x2wq/7CrB1pjzaJSo7bqs= 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-495-6CB_kVIDPUWcSs8JuT5UhQ-1; Mon, 01 Mar 2021 11:33:31 -0500 X-MC-Unique: 6CB_kVIDPUWcSs8JuT5UhQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9104780196C; Mon, 1 Mar 2021 16:33:30 +0000 (UTC) Received: from horse.redhat.com (ovpn-115-182.rdu2.redhat.com [10.10.115.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id 67022620DE; Mon, 1 Mar 2021 16:33:25 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id F035822054F; Mon, 1 Mar 2021 11:33:24 -0500 (EST) Date: Mon, 1 Mar 2021 11:33:24 -0500 From: Vivek Goyal To: Luis Henriques Cc: Miklos Szeredi , linux-fsdevel@vger.kernel.org, virtio-fs@redhat.com, linux-kernel@vger.kernel.org, "Dr. David Alan Gilbert" Subject: Re: [RFC PATCH] fuse: Clear SGID bit when setting mode in setacl Message-ID: <20210301163324.GC186178@redhat.com> References: <20210226183357.28467-1-lhenriques@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210226183357.28467-1-lhenriques@suse.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 26, 2021 at 06:33:57PM +0000, Luis Henriques wrote: > Setting file permissions with POSIX ACLs (setxattr) isn't clearing the > setgid bit. This seems to be CVE-2016-7097, detected by running fstest > generic/375 in virtiofs. Unfortunately, when the fix for this CVE landed > in the kernel with commit 073931017b49 ("posix_acl: Clear SGID bit when > setting file permissions"), FUSE didn't had ACLs support yet. Hi Luis, Interesting. I did not know that "chmod" can lead to clearing of SGID as well. Recently we implemented FUSE_HANDLE_KILLPRIV_V2 flag which means that file server is responsible for clearing of SUID/SGID/caps as per following rules. - caps are always cleared on chown/write/truncate - suid is always cleared on chown, while for truncate/write it is cleared only if caller does not have CAP_FSETID. - sgid is always cleared on chown, while for truncate/write it is cleared only if caller does not have CAP_FSETID as well as file has group execute permission. And we don't have anything about "chmod" in this list. Well, I will test this and come back to this little later. I see following comment in fuse_set_acl(). /* * Fuse userspace is responsible for updating access * permissions in the inode, if needed. fuse_setxattr * invalidates the inode attributes, which will force * them to be refreshed the next time they are used, * and it also updates i_ctime. */ So looks like that original code has been written with intent that file server is responsible for updating inode permissions. I am assuming this will include clearing of S_ISGID if needed. But question is, does file server has enough information to be able to handle proper clearing of S_ISGID info. IIUC, file server will need two pieces of information atleast. - gid of the caller. - Whether caller has CAP_FSETID or not. I think we have first piece of information but not the second one. May be we need to send this in fuse_setxattr_in->flags. And file server can drop CAP_FSETID while doing setxattr(). What about "gid" info. We don't change to caller's uid/gid while doing setxattr(). So host might not clear S_ISGID or clear it when it should not. I am wondering that can we switch to caller's uid/gid in setxattr(), atleast while setting acls. Thanks Vivek > > Signed-off-by: Luis Henriques > --- > fs/fuse/acl.c | 29 ++++++++++++++++++++++++++--- > 1 file changed, 26 insertions(+), 3 deletions(-) > > diff --git a/fs/fuse/acl.c b/fs/fuse/acl.c > index f529075a2ce8..1b273277c1c9 100644 > --- a/fs/fuse/acl.c > +++ b/fs/fuse/acl.c > @@ -54,7 +54,9 @@ int fuse_set_acl(struct inode *inode, struct posix_acl *acl, int type) > { > struct fuse_conn *fc = get_fuse_conn(inode); > const char *name; > + umode_t mode = inode->i_mode; > int ret; > + bool update_mode = false; > > if (fuse_is_bad(inode)) > return -EIO; > @@ -62,11 +64,18 @@ int fuse_set_acl(struct inode *inode, struct posix_acl *acl, int type) > if (!fc->posix_acl || fc->no_setxattr) > return -EOPNOTSUPP; > > - if (type == ACL_TYPE_ACCESS) > + if (type == ACL_TYPE_ACCESS) { > name = XATTR_NAME_POSIX_ACL_ACCESS; > - else if (type == ACL_TYPE_DEFAULT) > + if (acl) { > + ret = posix_acl_update_mode(inode, &mode, &acl); > + if (ret) > + return ret; > + if (inode->i_mode != mode) > + update_mode = true; > + } > + } else if (type == ACL_TYPE_DEFAULT) { > name = XATTR_NAME_POSIX_ACL_DEFAULT; > - else > + } else > return -EINVAL; > > if (acl) { > @@ -98,6 +107,20 @@ int fuse_set_acl(struct inode *inode, struct posix_acl *acl, int type) > } else { > ret = fuse_removexattr(inode, name); > } > + if (!ret && update_mode) { > + struct dentry *entry; > + struct iattr attr; > + > + entry = d_find_alias(inode); > + if (entry) { > + memset(&attr, 0, sizeof(attr)); > + attr.ia_valid = ATTR_MODE | ATTR_CTIME; > + attr.ia_mode = mode; > + attr.ia_ctime = current_time(inode); > + ret = fuse_do_setattr(entry, &attr, NULL); > + dput(entry); > + } > + } > forget_all_cached_acls(inode); > fuse_invalidate_attr(inode); > >