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=-20.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_NONE, USER_AGENT_SANE_1 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 CFA1EC433B4 for ; Wed, 12 May 2021 15:38:23 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2AE8C61D19 for ; Wed, 12 May 2021 15:38:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2AE8C61D19 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 ([::1]:46638 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lgqwH-0007xP-SO for qemu-devel@archiver.kernel.org; Wed, 12 May 2021 11:38:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50766) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lgqub-0005yi-VK for qemu-devel@nongnu.org; Wed, 12 May 2021 11:36:37 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41186) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lgquZ-0003DS-LJ for qemu-devel@nongnu.org; Wed, 12 May 2021 11:36:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620833794; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Oe2RseuvS3c7iCYv1fxJ68r0oNItMyp9I6uxqBWSnA0=; b=BzFOMY8dkGW2EAfqLagxaQz941N9srRq5I4GjTUZ+7waAk4dF0JHrz7K6/cVdGbHYf0xrL e70WZDBVXueASzY72WYON6TKNa64JGVXf6cjc80KT2OnLnK8EvP4qaexhiQyMyu5mKbdpj CjZBmU7cf4t7e/sN66890ttWkSXLol8= 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-343-c8ekOx1SMeSrmSwtkiUUuA-1; Wed, 12 May 2021 11:36:32 -0400 X-MC-Unique: c8ekOx1SMeSrmSwtkiUUuA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EFC9E1020C37 for ; Wed, 12 May 2021 15:36:31 +0000 (UTC) Received: from redhat.com (ovpn-114-167.ams2.redhat.com [10.36.114.167]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E38305D9D7; Wed, 12 May 2021 15:36:30 +0000 (UTC) Date: Wed, 12 May 2021 16:36:27 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH 2/2] net/tap: fix error reporting when bridge helper forgets to send an FD Message-ID: References: <20210505121236.532755-1-berrange@redhat.com> <20210505121236.532755-3-berrange@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.6 (2021-03-06) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Jason Wang , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 05, 2021 at 02:32:04PM +0200, Philippe Mathieu-Daudé wrote: > On 5/5/21 2:12 PM, Daniel P. Berrangé wrote: > > The recv_fd() method returns -1 on error, 0 on end of file, or an FD > > number on success. > > > > Technically 0 is also a valid FD number, so the return value is > > ambiguous. > > > > The caller doesn't even consider the possibility of 0 meaning end > > of file, so just blindly assume it is a valid FD. > > > > IOW if the bridge helper exits with 0 status code and forgets to > > send an FD, QEMU will accidentally try to use STDIN as a TAP FD. > > > > Fortunately we get an error shortly thereafter > > > > $ qemu-system-x86_64 -netdev bridge,br=br99,helper=/bin/true,id=ns0 > > qemu-system-x86_64: -netdev bridge,br=br99,helper=/bin/true,id=ns0: > > Unable to query TUNGETIFF on FD 0: Inappropriate ioctl for device > > > > It is better if we correctly diagnose this broken bridge helper > > though. To do this we need to return the FD in an output parameter > > to remove the ambiguity and then fix the caller to check for the > > end of file condition. With this done we now get > > > > $ qemu-system-x86_64 -netdev bridge,br=br99,helper=/bin/true,id=ns0 > > qemu-system-x86_64: -netdev bridge,br=br99,helper=/bin/true,id=ns0: > > bridge helper did not send a file descriptor > > > > Fixes: https://gitlab.com/qemu-project/qemu/-/issues/166 > > Signed-off-by: Daniel P. Berrangé > > --- > > net/tap.c | 32 ++++++++++++++++++++++---------- > > 1 file changed, 22 insertions(+), 10 deletions(-) > > > + /* > > + * ret == 0 means EOF, and if status == 0 then helper > > + * exited cleanly but forgot to send us an FD. Opps... > > Opps or Oops? Oops, it should be Oops :-) > > Otherwise: > Reviewed-by: Philippe Mathieu-Daudé > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|