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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 B8F56C433E0 for ; Wed, 10 Mar 2021 13:50:28 +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 2BB3264FD9 for ; Wed, 10 Mar 2021 13:50:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2BB3264FD9 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]:52122 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJzEJ-0008F8-4X for qemu-devel@archiver.kernel.org; Wed, 10 Mar 2021 08:50:27 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:53862) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJzDC-0007SV-Sk for qemu-devel@nongnu.org; Wed, 10 Mar 2021 08:49:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41711) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lJzD9-0001uT-6n for qemu-devel@nongnu.org; Wed, 10 Mar 2021 08:49:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615384153; 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=cQB0inF29EZBPxDYY+ISS0J0gN46p8KEMcnHzrhqnBA=; b=gTlAvK0PSbbAN4Jie4z3x+ceknoOG/Rk2pF5h4AN6w9fnvyAXkCBv7YbSP71z2At5qXT1R 8Tgsk6t3A7WkexQO3V9Ep70iwg2QqgT5QeHCK0v8MuLBbVaZ1J0sfWvaJLrLYR6m3an/5S dtiMXGztax+dWkpwz5httrCuZFFpEhA= 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-304-BQgQHewgMYuSOLUmaaebQg-1; Wed, 10 Mar 2021 08:49:08 -0500 X-MC-Unique: BQgQHewgMYuSOLUmaaebQg-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 8DB9A80D686; Wed, 10 Mar 2021 13:49:07 +0000 (UTC) Received: from redhat.com (ovpn-115-24.ams2.redhat.com [10.36.115.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A374C5DEF9; Wed, 10 Mar 2021 13:48:50 +0000 (UTC) Date: Wed, 10 Mar 2021 13:48:46 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Greg Kurz Subject: Re: [PATCH 2/4] vhost-user: Convert slave channel to QIOChannelSocket Message-ID: References: <20210308123141.26444-1-groug@kaod.org> <20210308123141.26444-3-groug@kaod.org> <20210309212322.3ab5809d@bahia.lan> <20210310144525.40935330@bahia.lan> MIME-Version: 1.0 In-Reply-To: <20210310144525.40935330@bahia.lan> User-Agent: Mutt/2.0.5 (2021-01-21) 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=63.128.21.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.243, 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: "Michael S. Tsirkin" , Stefan Hajnoczi , "Dr. David Alan Gilbert" , Vivek Goyal , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Mar 10, 2021 at 02:45:25PM +0100, Greg Kurz wrote: > On Wed, 10 Mar 2021 11:43:58 +0000 > Daniel P. Berrangé wrote: > > > On Tue, Mar 09, 2021 at 09:23:22PM +0100, Greg Kurz wrote: > > > On Tue, 9 Mar 2021 15:17:21 +0000 > > > Stefan Hajnoczi wrote: > > > > > > > On Mon, Mar 08, 2021 at 01:31:39PM +0100, Greg Kurz wrote: > > > > > + g_autofree int *fd = NULL; > > > > > + size_t fdsize = 0; > > > > > + int i; > > > > > > > > > > /* Read header */ > > > > > iov.iov_base = &hdr; > > > > > iov.iov_len = VHOST_USER_HDR_SIZE; > > > > > > > > > > do { > > > > > - size = recvmsg(u->slave_fd, &msgh, 0); > > > > > - } while (size < 0 && (errno == EINTR || errno == EAGAIN)); > > > > > + size = qio_channel_readv_full(ioc, &iov, 1, &fd, &fdsize, NULL); > > > > > + } while (size == QIO_CHANNEL_ERR_BLOCK); > > > > > > > > Is it possible to leak file descriptors and fd[] memory if we receive a > > > > short message and then loop around? qio_channel_readv_full() will > > > > overwrite &fd and that's how the leak occurs. > > > > > > > > > > qio_channel_readv_full() only returns QIO_CHANNEL_ERR_BLOCK when the > > > channel is non-blocking mode and no data is available. Under the hood, > > > this translates to this code in qio_channel_socket_readv(): > > > > > > retry: > > > ret = recvmsg(sioc->fd, &msg, sflags); > > > if (ret < 0) { > > > if (errno == EAGAIN) { > > > return QIO_CHANNEL_ERR_BLOCK; > > > } > > > if (errno == EINTR) { > > > goto retry; > > > } > > > > > > error_setg_errno(errp, errno, > > > "Unable to read from socket"); > > > return -1; > > > } > > > > > > This is strictly equivalent to what we currently have. This cannot > > > leak file descriptors because we would only loop until the first > > > byte of real data is available and ancillary data cannot fly without > > > real data, i.e. no file descriptors when recvmsg() returns EAGAIN. > > > > Yep, EAGAIN will only happen if you have no data AND no FDs. > > > > > > > > > On the other hand, it looks like ioc is in blocking mode. I'm not sure > > > > QIO_CHANNEL_ERR_BLOCK can occur? > > > > > > > > > > You're right but the existing code is ready to handle the non-blocking > > > case, so I just kept this behavior. > > > > The existing code is *not* handling the non-blocking case in any > > useful way IMHO. It will block execution of this QEMU thread, and > > sit in a tight loop burning CPU in the EAGAIN case. > > > > Handling non-blocking means using an I/O watch with the event loop > > to be notified when something becomes ready. > > > > Hmm... slave_read() is a handler registered with qemu_set_fd_handler(). > Isn't it already the case then ? Can the first call to recvmsg() even > return EAGAIN actually ? IIUC it shouldn't be able to return EAGAIN in that scenario for stream sockets (TCP, UNIX), only a datagram socket (UDP) would be at risk of EAGAIN 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 :|