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=-4.1 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 2B37EC433DF for ; Tue, 21 Jul 2020 15:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F29D42073A for ; Tue, 21 Jul 2020 15:55:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Dk9VXrU2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728219AbgGUPzO (ORCPT ); Tue, 21 Jul 2020 11:55:14 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:49370 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726029AbgGUPzO (ORCPT ); Tue, 21 Jul 2020 11:55:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595346912; 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=XU2KlFmxoaRSSLSNlW5R1k7uon9KSmk8HhOfo5+I89I=; b=Dk9VXrU2l3eGvzFFXnF4s+yOolyy0rpBqjTWRr5Z8stdup5PBfro6MiVJB7qfqojCY82eJ NakinNeFVo6Fhp4L8CVuiIaJjgB1myHR9j7w7g0I32ro1uj4SBG7SorNUfjXSqSi9S584b iMxc3PTdjIMaeLsb82S/AGKj2iN3HGM= 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-437-m_OZkfUPPH-LOnr3EVCSkA-1; Tue, 21 Jul 2020 11:55:08 -0400 X-MC-Unique: m_OZkfUPPH-LOnr3EVCSkA-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 1E1ECE918; Tue, 21 Jul 2020 15:55:07 +0000 (UTC) Received: from horse.redhat.com (ovpn-116-14.rdu2.redhat.com [10.10.116.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id D9BA52B580; Tue, 21 Jul 2020 15:55:03 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 68ACD223C1E; Tue, 21 Jul 2020 11:55:03 -0400 (EDT) Date: Tue, 21 Jul 2020 11:55:03 -0400 From: Vivek Goyal To: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org, virtio-fs-list , ganesh.mahalingam@intel.com Subject: Re: [PATCH] virtiofs: Enable SB_NOSEC flag to improve small write performance Message-ID: <20200721155503.GC551452@redhat.com> References: <20200716144032.GC422759@redhat.com> <20200716181828.GE422759@redhat.com> <20200720154112.GC502563@redhat.com> <20200721151655.GB551452@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jul 21, 2020 at 05:44:14PM +0200, Miklos Szeredi wrote: > On Tue, Jul 21, 2020 at 5:17 PM Vivek Goyal wrote: > > > > On Tue, Jul 21, 2020 at 02:33:41PM +0200, Miklos Szeredi wrote: > > > On Mon, Jul 20, 2020 at 5:41 PM Vivek Goyal wrote: > > > > > > > > On Fri, Jul 17, 2020 at 10:53:07AM +0200, Miklos Szeredi wrote: > > > > > > > I see in VFS that chown() always kills suid/sgid. While truncate() and > > > > write(), will suid/sgid only if caller does not have CAP_FSETID. > > > > > > > > How does this work with FUSE_HANDLE_KILLPRIV. IIUC, file server does not > > > > know if caller has CAP_FSETID or not. That means file server will be > > > > forced to kill suid/sgid on every write and truncate. And that will fail > > > > some of the tests. > > > > > > > > For WRITE requests now we do have the notion of setting > > > > FUSE_WRITE_KILL_PRIV flag to tell server explicitly to kill suid/sgid. > > > > Probably we could use that in cached write path as well to figure out > > > > whether to kill suid/sgid or not. But truncate() will still continue > > > > to be an issue. > > > > > > Yes, not doing the same for truncate seems to be an oversight. > > > Unfortunate, since we'll need another INIT flag to enable selective > > > clearing of suid/sgid on truncate. > > > > > > > > > > > > > > > > > Even writeback_cache could be handled by this addition, since we call > > > > > fuse_update_attributes() before generic_file_write_iter() : > > > > > > > > > > --- a/fs/fuse/dir.c > > > > > +++ b/fs/fuse/dir.c > > > > > @@ -985,6 +985,7 @@ static int fuse_update_get_attr(struct inode > > > > > *inode, struct file *file, > > > > > > > > > > if (sync) { > > > > > forget_all_cached_acls(inode); > > > > > + inode->i_flags &= ~S_NOSEC; > > > > > > > > Ok, So I was clearing S_NOSEC only if server reports that file has > > > > suid/sgid bit set. This change will clear S_NOSEC whenever we fetch > > > > attrs from host and will force getxattr() when we call file_remove_privs() > > > > and will increase overhead for non cache writeback mode. We probably > > > > could keep both. For cache writeback mode, clear it undonditionally > > > > otherwise not. > > > > > > We clear S_NOSEC because the attribute timeout has expired. This > > > means we need to refresh all metadata, including cached xattr (which > > > is what S_NOSEC effectively is). > > > > > > > What I don't understand is though that how this change will clear > > > > suid/sgid on host in cache=writeback mode. I see fuse_setattr() > > > > will not set ATTR_MODE and clear S_ISUID and S_ISGID if > > > > fc->handle_killpriv is set. So when server receives setattr request > > > > (if it does), then how will it know it is supposed to kill suid/sgid > > > > bit. (its not chown, truncate and its not write). > > > > > > Depends. If the attribute timeout is infinity, then that means the > > > cache is always up to date. In that case we only need to clear > > > suid/sgid if set in i_mode. Similarly, the security.capability will > > > only be cleared if it was set in the first place (which would clear > > > S_NOSEC). > > > > > > If the timeout is finite, then that means we need to check if the > > > metadata changed after a timeout. That's the purpose of the > > > fuse_update_attributes() call before generic_file_write_iter(). > > > > > > Does that make it clear? > > > > I understood it partly but one thing is still bothering me. What > > happens when cache writeback is set as well as fc->handle_killpriv=1. > > > > When handle_killpriv is set, how suid/sgid will be cleared by > > server. Given cache=writeback, write probably got cached in > > guest and server probably will not not see a WRITE immideately. > > (I am assuming we are relying on a WRITE to clear setuid/setgid when > > handle_killpriv is set). And that means server will not clear > > setuid/setgid till inode is written back at some point of time > > later. > > > > IOW, cache=writeback and fc->handle_killpriv don't seem to go > > together (atleast given the current code). > > fuse_cache_write_iter() > -> fuse_update_attributes() * this will refresh i_mode > -> generic_file_write_iter() > ->__generic_file_write_iter() > ->file_remove_privs() * this will check i_mode > ->__remove_privs() > -> notify_change() > -> fuse_setattr() * this will clear suid/sgit bits And fuse_setattr() has following. if (!fc->handle_killpriv) { /* * ia_mode calculation may have used stale i_mode. * Refresh and recalculate. */ ret = fuse_do_getattr(inode, NULL, file); if (ret) return ret; attr->ia_mode = inode->i_mode; if (inode->i_mode & S_ISUID) { attr->ia_valid |= ATTR_MODE; attr->ia_mode &= ~S_ISUID; } if ((inode->i_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { attr->ia_valid |= ATTR_MODE; attr->ia_mode &= ~S_ISGID; } } } if (!attr->ia_valid) return 0; So if fc->handle_killpriv is set, we might not even send setattr request if attr->ia_valid turns out to be zero. I did a quick instrumentation and noticed that we are sending setattr with attr->ia_valid=0x200 (ATTR_FORCE) set. And file server is not required to kill suid/sgid in this case? Thanks Vivek