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=-2.4 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 D47E4C04E53 for ; Wed, 15 May 2019 14:58:56 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 992BF206BF for ; Wed, 15 May 2019 14:58:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 992BF206BF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:38231 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQvMq-0002Mf-4L for qemu-devel@archiver.kernel.org; Wed, 15 May 2019 10:58:52 -0400 Received: from eggs.gnu.org ([209.51.188.92]:37574) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQvL5-0001HP-FS for qemu-devel@nongnu.org; Wed, 15 May 2019 10:57:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQvJr-0001D4-Vy for qemu-devel@nongnu.org; Wed, 15 May 2019 10:55:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45334) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQvJr-0001CM-Nk for qemu-devel@nongnu.org; Wed, 15 May 2019 10:55:47 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D82653003194; Wed, 15 May 2019 14:55:41 +0000 (UTC) Received: from redhat.com (ovpn-112-65.ams2.redhat.com [10.36.112.65]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D8E811001943; Wed, 15 May 2019 14:55:37 +0000 (UTC) Date: Wed, 15 May 2019 15:55:35 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Message-ID: <20190515145535.GI4751@redhat.com> References: <20190418145355.21100-1-armbru@redhat.com> <20190418145355.21100-2-armbru@redhat.com> <2679829b-cc1d-83ce-9949-2b80d970ddec@redhat.com> <875zqe7b10.fsf@dusky.pond.sub.org> <877eat6xgm.fsf@dusky.pond.sub.org> <87lfz88bva.fsf@dusky.pond.sub.org> <20190515102615.GB4751@redhat.com> <87a7fn6a5v.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87a7fn6a5v.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 15 May 2019 14:55:41 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 1/6] qemu-bridge-helper: Fix misuse of isspace() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , Jason Wang , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , QEMU Developers , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 15, 2019 at 04:54:04PM +0200, Markus Armbruster wrote: > Daniel P. Berrang=C3=A9 writes: >=20 > > On Wed, May 15, 2019 at 08:34:17AM +0200, Markus Armbruster wrote: > >> Jason Wang writes: > >>=20 > >> > On 2019/5/14 =E4=B8=8B=E5=8D=888:18, Markus Armbruster wrote: > >> >> Peter Maydell writes: > >> >> > >> >>> On Mon, 13 May 2019 at 14:21, Markus Armbruster wrote: > >> >>>> Perhaps I should do it just for this file while I touch it anyw= ay. The > >> >>>> question to ask: should parse_acl_file() obey the locale for wh= itespace > >> >>>> recognition? > >> >>> I vote for "no". > >> >>> > >> >>> Q: do we document the format of the ACL file anywhere ? > >> >> Support for it was added in commit bdef79a2994, v1.1. Just code,= no > >> >> documentation. > >> >> > >> >> Grepping for qemu-bridge-helper finds just qemu-options.hx. Cont= ains > >> >> -help output and some .texi that goes into qemu-doc and the manua= l page. > >> >> None of it mentions how qemu-bridge-helper is run, or the ACL fil= e > >> >> feature, let alone what its format might be. > >> >> > >> >> I'm afraid all we have is the commit message. Which doesn't real= ly > >> >> define the file format, it merely gives a bunch of examples. > >> >> > >> >> As far as I can tell, qemu-bridge-helper is for use with -netdev = tap and > >> >> -netdev bridge. > >> >> > >> >> Both variations of -netdev call net_bridge_run_helper() to run th= e > >> >> helper. First argument is -netdev parameter "helper", default us= ually > >> >> "$prefix/libexec/qemu-bridge-helper". Second argument is paramet= er > >> >> "br", default "br0". > >> >> > >> >> If @helper contains space or tab, net_bridge_run_helper() guesses= its a > >> >> full command, else it guesses its the name of the executable. Ba= d > >> >> magic. > >> >> > >> >> If it guesses name of executable, it execv()s this executable wit= h > >> >> arguments "--use-vnet", "--fd=3DFD", "--br=3D@bridge". > >> >> > >> >> If it guesses full command, it appends "--use-vnet --fd=3DFD", wh= ere FD is > >> >> the helper's half of the socketpair used to connect QEMU and the = helper. > >> >> It further appends "--br=3D@bridge", unless @helper contains "--b= r=3D". > >> >> More bad magic. > >> >> > >> >> It executes the resulting string with sh -c. Magic cherry on top= . > >> >> > >> >> When the helper fails, netdev creation fails. > >> >> > >> >> The helper we ship with QEMU unconditionally tries to read > >> >> "$prefix/etc/bridge.conf". Fatal error if this file doesn't exis= t. > >> >> Errors in this file are fatal. Errors in files it includes are n= ot > >> >> fatal; instead, the remainder of the erroneous file is ignored. > >> >> *Boggle* > >> >> > >> >> As far as I can tell, libvirt runs qemu-bridge-helper itself (Pao= lo's > >> >> commit 2d80fbb14df). Makes sense, because running QEMU with the > >> >> necessary privileges would be unwise, and so would be letting it = execute > >> >> setuid helpers. Also bypasses the bad magic in QEMU's > >> >> net_bridge_run_helper(). > >> > > >> > > >> > I don't notice this before. Is this only for the convenience of > >> > development? I guess libvirt should have native support like addin= g > >> > port to bridge/OVS without the help any external command or script= . > >>=20 > >> Commit 2d80fbb14df hints at the reason: > >>=20 > >> uses a helper application to do the nec= essary > >> TUN/TAP setup to use an existing network bridge, thus letting > >> unprivileged users use TUN/TAP interfaces. > >> ~~~~~~~~~~~~~~~~~~ > >>=20 > >> The code confirms: > >>=20 > >> /* qemuInterfaceBridgeConnect: > >> * @def: the definition of the VM > >> * @driver: qemu driver data > >> * @net: pointer to the VM's interface description > >> * @tapfd: array of file descriptor return value for the new dev= ice > >> * @tapfdsize: number of file descriptors in @tapfd > >> * > >> ---> * Called *only* called if actualType is VIR_DOMAIN_NET_TYPE_NET= WORK or > >> ---> * VIR_DOMAIN_NET_TYPE_BRIDGE (i.e. if the connection is made wi= th a tap > >> * device connecting to a bridge device) > >> */ > >> int > >> qemuInterfaceBridgeConnect(virDomainDefPtr def, > >> virQEMUDriverPtr driver, > >> virDomainNetDefPtr net, > >> int *tapfd, > >> size_t *tapfdSize) > >> { > >> [...] > >> ---> if (virQEMUDriverIsPrivileged(driver)) { > >> [...] > >> } else { > >> if (qemuCreateInBridgePortWithHelper(cfg, brname, > >> &net->ifname, > >> tapfd, tap_create_f= lags) < 0) { > >> virDomainAuditNetDevice(def, net, tunpath, false); > >> goto cleanup; > >> } > >> [...] > >> } > >> [...] > >> } > >>=20 > >> >> qemu-bridge-helper should have a manual page, and its handling of= errors > >> >> in ACL include files needs work. There's probably more; I just g= lanced > >> >> at it. I'm not volunteering, though. It lacks a maintainer. Sh= ould we > >> >> add it to Jason's "Network device backends"? > >> > > >> > > >> > Yes. > >> > > >> >> -netdev's helper parameter is seriously underdocumented. Documen= t or > >> >> deprecate? > >> > > >> > > >> > I believe management should only use fd parameter of TAP. If we ha= ve > >> > other, it should be a duplication. So I suggest to deprecate the > >> > bridge helper and -netdev bridge. > >>=20 > >> Objections, anyone? > > > > Libvirt runs the qemu bridge helper command directly, and we have > > applications using this functionality. >=20 > Specifically, when libvirt lacks the privileges to set up a TAP fd, it > farms out the job to setuid qemu-bridge-helper. Correct? Yes, this is for when using libvirt as an unpriv user - typically the desktop virt use case. > > I'd like libvirt to be able to avoid use of the QEMU bridge helper an= d > > instead have unprivileged libvirt talk to privileged libvirtd to open= a > > TAP fd on its behalf. If we ever get that done, then libvirt would no= t > > need the qemu bridge helper command anymore. >=20 > We don't want to deprecate qemu-bridge-helper while libvirt has a > sensible use for it. >=20 > We can still deprecate -netdev tap parameter "helper" and -netdev bridg= e > entirely. No objection to that. > Once they're gone, qemu-bridge-helper wull have no user within QEMU. W= e > could discuss moving it to libvirt then, but I doubt it'll be worth the > trouble. I'm fine with that either way. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|