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 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 BD8BCC04E87 for ; Wed, 15 May 2019 14:59:12 +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 83572206BF for ; Wed, 15 May 2019 14:59:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83572206BF 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]:38235 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQvN9-0002bE-R6 for qemu-devel@archiver.kernel.org; Wed, 15 May 2019 10:59:11 -0400 Received: from eggs.gnu.org ([209.51.188.92]:37580) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQvLE-0001HS-OS for qemu-devel@nongnu.org; Wed, 15 May 2019 10:57:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQvIW-00006i-4U for qemu-devel@nongnu.org; Wed, 15 May 2019 10:54:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34930) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQvIP-0008Li-55 for qemu-devel@nongnu.org; Wed, 15 May 2019 10:54:19 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 4621D300DA33; Wed, 15 May 2019 14:54:07 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-28.ams2.redhat.com [10.36.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D9B1919C7C; Wed, 15 May 2019 14:54:06 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 5C94911385E4; Wed, 15 May 2019 16:54:04 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= 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> Date: Wed, 15 May 2019 16:54:04 +0200 In-Reply-To: <20190515102615.GB4751@redhat.com> ("Daniel P. =?utf-8?Q?Berr?= =?utf-8?Q?ang=C3=A9=22's?= message of "Wed, 15 May 2019 11:26:15 +0100") Message-ID: <87a7fn6a5v.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 15 May 2019 14:54:10 +0000 (UTC) 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: , 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" Daniel P. Berrang=C3=A9 writes: > 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 anyway. = The >> >>>> question to ask: should parse_acl_file() obey the locale for whites= pace >> >>>> 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. Contains >> >> -help output and some .texi that goes into qemu-doc and the manual pa= ge. >> >> None of it mentions how qemu-bridge-helper is run, or the ACL file >> >> feature, let alone what its format might be. >> >> >> >> I'm afraid all we have is the commit message. Which doesn't really >> >> 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 the >> >> helper. First argument is -netdev parameter "helper", default usually >> >> "$prefix/libexec/qemu-bridge-helper". Second argument is parameter >> >> "br", default "br0". >> >> >> >> If @helper contains space or tab, net_bridge_run_helper() guesses its= a >> >> full command, else it guesses its the name of the executable. Bad >> >> magic. >> >> >> >> If it guesses name of executable, it execv()s this executable with >> >> arguments "--use-vnet", "--fd=3DFD", "--br=3D@bridge". >> >> >> >> If it guesses full command, it appends "--use-vnet --fd=3DFD", where = FD is >> >> the helper's half of the socketpair used to connect QEMU and the help= er. >> >> It further appends "--br=3D@bridge", unless @helper contains "--br=3D= ". >> >> More bad magic. >> >> >> >> It executes the resulting string with sh -c. Magic cherry on top. >> >> >> >> When the helper fails, netdev creation fails. >> >> >> >> The helper we ship with QEMU unconditionally tries to read >> >> "$prefix/etc/bridge.conf". Fatal error if this file doesn't exist. >> >> Errors in this file are fatal. Errors in files it includes are not >> >> fatal; instead, the remainder of the erroneous file is ignored. >> >> *Boggle* >> >> >> >> As far as I can tell, libvirt runs qemu-bridge-helper itself (Paolo's >> >> commit 2d80fbb14df). Makes sense, because running QEMU with the >> >> necessary privileges would be unwise, and so would be letting it exec= ute >> >> 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 adding >> > 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 necessa= ry >> 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 device >> * @tapfdsize: number of file descriptors in @tapfd >> * >> ---> * Called *only* called if actualType is VIR_DOMAIN_NET_TYPE_NETWORK= or >> ---> * VIR_DOMAIN_NET_TYPE_BRIDGE (i.e. if the connection is made with 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_flags= ) < 0) { >> virDomainAuditNetDevice(def, net, tunpath, false); >> goto cleanup; >> } >> [...] >> } >> [...] >> } >>=20 >> >> qemu-bridge-helper should have a manual page, and its handling of err= ors >> >> in ACL include files needs work. There's probably more; I just glanc= ed >> >> at it. I'm not volunteering, though. It lacks a maintainer. Should= we >> >> add it to Jason's "Network device backends"? >> > >> > >> > Yes. >> > >> >> -netdev's helper parameter is seriously underdocumented. Document or >> >> deprecate? >> > >> > >> > I believe management should only use fd parameter of TAP. If we have >> > 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. Specifically, when libvirt lacks the privileges to set up a TAP fd, it farms out the job to setuid qemu-bridge-helper. Correct? > I'd like libvirt to be able to avoid use of the QEMU bridge helper and > 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 not > need the qemu bridge helper command anymore. We don't want to deprecate qemu-bridge-helper while libvirt has a sensible use for it. We can still deprecate -netdev tap parameter "helper" and -netdev bridge entirely. Once they're gone, qemu-bridge-helper wull have no user within QEMU. We could discuss moving it to libvirt then, but I doubt it'll be worth the trouble.