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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 BF297C43219 for ; Thu, 2 May 2019 14:05:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EB942089E for ; Thu, 2 May 2019 14:05:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726320AbfEBOFD convert rfc822-to-8bit (ORCPT ); Thu, 2 May 2019 10:05:03 -0400 Received: from mail-oi1-f193.google.com ([209.85.167.193]:36504 "EHLO mail-oi1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbfEBOFC (ORCPT ); Thu, 2 May 2019 10:05:02 -0400 Received: by mail-oi1-f193.google.com with SMTP id l203so1777705oia.3 for ; Thu, 02 May 2019 07:05:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=4IqJbBFrVtTZ0oqzJ67Gm9A7iC2geeoklI44WKE5eEI=; b=Uw/m6o0bhRw7wPs6S6yKkc1avKd8ohjjITE5Gx/wCNdcxD8/MlSNPczIsjHcGuuBzX llC/BKakXncwU/3ClnBpsJmKJIyhImxOyx0kv/RcBeJIG8dSUTcmt9ihPqaZ9H+ZHJMP wbwsO74CDoCucupRqtnAQeM2+gvxfPfuwEiwJGdNcrZv0h2JEtQxdCj9dtMPDjnlTA+7 o4lhabaLi8Md5olSsuHUjBKw/HeEXBacdqtxpa2yUaLpyQQoFGrRBRjZFu7uXxw6joqI n0JaeFpEfn8k1zm0OjMNswhTLqKGvJ3lAxRfp46N3LrUcEjXRCuieXRBiR1Na+AQgPgi w5zA== X-Gm-Message-State: APjAAAXA8SfzBy8NsmeONeogNrvS1G8fuRHUx/9OvEIzWn9poftg9RdE KCp4eVUCQHFe2aL33lgGtDNOjq/iRS7QIxCMC5udHA== X-Google-Smtp-Source: APXvYqxQaPoecIhQ0ywakL0+8rFGAnEtV+06xebpZjZ4MXPOOp6535GBw75TR32zAWw/jHJ5jS5EoUX8/OA/7dCk4P0= X-Received: by 2002:aca:f086:: with SMTP id o128mr2371553oih.101.1556805901943; Thu, 02 May 2019 07:05:01 -0700 (PDT) MIME-Version: 1.0 References: <20161205151933.GA17517@fieldses.org> <20161205162559.GB17517@fieldses.org> <266c571f-e4e2-7c61-5ee2-8ece0c2d06e9@web.de> <20161206185806.GC31197@fieldses.org> <87bm0l4nra.fsf@notabene.neil.brown.name> <875zqt4igg.fsf@notabene.neil.brown.name> In-Reply-To: <875zqt4igg.fsf@notabene.neil.brown.name> From: Andreas Gruenbacher Date: Thu, 2 May 2019 16:04:50 +0200 Message-ID: Subject: Re: [PATCH] overlayfs: ignore empty NFSv4 ACLs in ext4 upperdir To: NeilBrown Cc: Amir Goldstein , "J. Bruce Fields" , Miklos Szeredi , =?UTF-8?Q?Andreas_Gr=C3=BCnbacher?= , Patrick Plagwitz , "linux-unionfs@vger.kernel.org" , Linux NFS list , Linux FS-devel Mailing List , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Thu, 2 May 2019 at 05:57, NeilBrown wrote: > On Wed, May 01 2019, Amir Goldstein wrote: > > On Wed, May 1, 2019 at 10:03 PM NeilBrown wrote: > >> On Tue, Dec 06 2016, J. Bruce Fields wrote: > >> > On Tue, Dec 06, 2016 at 02:18:31PM +0100, Andreas Gruenbacher wrote: > >> >> On Tue, Dec 6, 2016 at 11:08 AM, Miklos Szeredi wrote: > >> >> > On Tue, Dec 6, 2016 at 12:24 AM, Andreas Grünbacher > >> >> > wrote: > >> >> >> 2016-12-06 0:19 GMT+01:00 Andreas Grünbacher : > >> >> > > >> >> >>> It's not hard to come up with a heuristic that determines if a > >> >> >>> system.nfs4_acl value is equivalent to a file mode, and to ignore the > >> >> >>> attribute in that case. (The file mode is transmitted in its own > >> >> >>> attribute already, so actually converting .) That way, overlayfs could > >> >> >>> still fail copying up files that have an actual ACL. It's still an > >> >> >>> ugly hack ... > >> >> >> > >> >> >> Actually, that kind of heuristic would make sense in the NFS client > >> >> >> which could then hide the "system.nfs4_acl" attribute. I still think the nfs client could make this problem mostly go away by not exposing "system.nfs4_acl" xattrs when the acl is equivalent to the file mode. The richacl patches contain a workable abgorithm for that. The problem would remain for files that have an actual NFS4 ACL, which just cannot be mapped to a file mode or to POSIX ACLs in the general case, as well as for files that have a POSIX ACL. Mapping NFS4 ACL that used to be a POSIX ACL back to POSIX ACLs could be achieved in many cases as well, but the code would be quite messy. A better way seems to be to using a filesystem that doesn't support POSIX ACLs in the first place. Unfortunately, xfs doesn't allow turning off POSIX ACLs, for example. Andreas > >> >> > Even simpler would be if knfsd didn't send the attribute if not > >> >> > necessary. Looks like there's code actively creating the nfs4_acl on > >> >> > the wire even if the filesystem had none: > >> >> > > >> >> > pacl = get_acl(inode, ACL_TYPE_ACCESS); > >> >> > if (!pacl) > >> >> > pacl = posix_acl_from_mode(inode->i_mode, GFP_KERNEL); > >> >> > > >> >> > What's the point? > >> >> > >> >> That's how the protocol is specified. > >> > > >> > Yep, even if we could make that change to nfsd it wouldn't help the > >> > client with the large number of other servers that are out there > >> > (including older knfsd's). > >> > > >> > --b. > >> > > >> >> (I'm not saying that that's very helpful.) > >> >> > >> >> Andreas > >> > >> Hi everyone..... > >> I have a customer facing this problem, and so stumbled onto the email > >> thread. > >> Unfortunately it didn't resolve anything. Maybe I can help kick things > >> along??? > >> > >> The core problem here is that NFSv4 and ext4 use different and largely > >> incompatible ACL implementations. There is no way to accurately > >> translate from one to the other in general (common specific examples > >> can be converted). > >> > >> This means that either: > >> 1/ overlayfs cannot use ext4 for upper and NFS for lower (or vice > >> versa) or > >> 2/ overlayfs need to accept that sometimes it cannot copy ACLs, and > >> that is OK. > >> > >> Silently not copying the ACLs is probably not a good idea as it might > >> result in inappropriate permissions being given away. > > > > For example? permissions given away to do what? > > Note that ovl_permission() only check permissions of *mounter* > > to read the lower NFS file and ovl_open()/ovl_read_iter() access > > the lower file with *mounter* credentials. > > > > I might be wrong, but seems to me that once admin mounted > > overlayfs with lower NFS, NFS ACLs are not being enforced at all > > even before copy up. > > I guess it is just as well that copy-up fails then - if the lower-level > permission check is being ignored. > > > > >> So if the > >> sysadmin wants this (and some clearly do), they need a way to > >> explicitly say "I accept the risk". If only standard Unix permissions > >> are used, there is no risk, so this seems reasonable. > >> > >> So I would like to propose a new option for overlayfs > >> nocopyupacl: when overlayfs is copying a file (or directory etc) > >> from the lower filesystem to the upper filesystem, it does not > >> copy extended attributes with the "system." prefix. These are > >> used for storing ACL information and this is sometimes not > >> compatible between different filesystem types (e.g. ext4 and > >> NFSv4). Standard Unix ownership permission flags (rwx) *are* > >> copied so this option does not risk giving away inappropriate > >> permissions unless the lowerfs uses unusual ACLs. > >> > >> > > > > I am wondering if it would make more sense for nfs to register a > > security_inode_copy_up_xattr() hook. > > That is the mechanism that prevents copying up other security.* > > xattrs? > > No, I don't think that would make sense. > Support some day support for nfs4 acls were added to ext4 (not a totally > ridiculous suggestion). We would then want NFS to allow it's ACLs to be > copied up. > > Thanks, > NeilBrown > > > > > > Thanks, > > Amir.