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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 02FF8C432C3 for ; Wed, 3 Mar 2021 05:38:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D761664EA4 for ; Wed, 3 Mar 2021 05:38:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237112AbhCCFYX (ORCPT ); Wed, 3 Mar 2021 00:24:23 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42626 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351434AbhCBOYv (ORCPT ); Tue, 2 Mar 2021 09:24:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614694974; 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=N3sSHK++R6zsz5fOVbw47mb0BUNgGRGZh9qrPGeQDx0=; b=LsTRMYpwxe7moxWb7DaO++tgzaGTZDvaWkSLFb5mpAj6rHlc+UkrGXwj/6ribQG7L6z0cT wbirxTI5Iqy7D1oYRuSHW2yJUnfe23JtGph1hZHp/hM2merxQRs/fmF8xzlFjhEcWc7X3v g+QmsKTfh32/CHCG2b4zXZYREa9HHPc= 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-555-U146o1jFM_OqzMLU63kT_A-1; Tue, 02 Mar 2021 09:22:52 -0500 X-MC-Unique: U146o1jFM_OqzMLU63kT_A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AB307107ACC7; Tue, 2 Mar 2021 14:22:51 +0000 (UTC) Received: from horse.redhat.com (ovpn-114-140.rdu2.redhat.com [10.10.114.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id 64D961971D; Tue, 2 Mar 2021 14:22:47 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id BAAD922054F; Tue, 2 Mar 2021 09:22:46 -0500 (EST) Date: Tue, 2 Mar 2021 09:22:46 -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: <20210302142246.GC220334@redhat.com> References: <20210226183357.28467-1-lhenriques@suse.de> <20210301163324.GC186178@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210301163324.GC186178@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Mar 01, 2021 at 11:33:24AM -0500, Vivek Goyal wrote: > 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. Looks like I did not notice the setattr_prepare() call in fuse_do_setattr() which clears SGID in client itself and server does not have to do anything extra. So it works. IOW, FUSE_HANDLE_KILLPRIV_V2 will not handle this particular case and fuse client will clear SGID on chmod, if need be. Vivek