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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 3D541C433E0 for ; Wed, 10 Mar 2021 11:50:13 +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 9C4E164F76 for ; Wed, 10 Mar 2021 11:50:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C4E164F76 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]:36544 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJxLv-0005KI-Gu for qemu-devel@archiver.kernel.org; Wed, 10 Mar 2021 06:50:11 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:54218) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJxGF-0008By-LV for qemu-devel@nongnu.org; Wed, 10 Mar 2021 06:44:19 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:49843) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lJxGD-0003Yx-Kz for qemu-devel@nongnu.org; Wed, 10 Mar 2021 06:44:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615376656; 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:in-reply-to:in-reply-to: references:references; bh=w9m+xUBVCQqJIx62naRE5hDFWNTNXaS0A37WOoit3qU=; b=VwuxFPbD9T9u44jpMrTRvSZsxbOmfHcIijHvUiwLaiQF7pzp8D7lZ7uZ2z2GHrK/3/2h0z w6abE15xW2S44mPp3A8COpHrsxH8t/iQfjl3cW/ipml60wnt14rc7GMgKGVE5SRKdHhVzM 2cBo+e7kCo3IVkvGYM7s60Wpdh7dh5A= 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-472-Cy8ctHvIMkWIBpGD87WvBg-1; Wed, 10 Mar 2021 06:44:11 -0500 X-MC-Unique: Cy8ctHvIMkWIBpGD87WvBg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 10F36804333; Wed, 10 Mar 2021 11:44:10 +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 9556460CE9; Wed, 10 Mar 2021 11:44:01 +0000 (UTC) Date: Wed, 10 Mar 2021 11:43:58 +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> MIME-Version: 1.0 In-Reply-To: <20210309212322.3ab5809d@bahia.lan> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 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=-0.251, 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: Vivek Goyal , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Stefan Hajnoczi , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. I notice the code that follows is also doing if (size != VHOST_USER_HDR_SIZE) { error_report("Failed to read from slave."); goto err; } which is also dubious because it assumes the previous recvmsg is guaranteed to return VHOST_USER_HDR_SIZE bytes of data in a single call. It does at least look like the code is intentionally blocking execution fo the QEMU thread until the expected amount of I/O is receieved. Given this, you should remove the while loop entirely and just call qio_channel_readv_full_all() this will block execution until *all* the requestd data bytes are read. It will re-try the recvmsg in the event of a partial data read, and will intelligently wait in poll() on EAGAIN. > > > > @@ -1500,8 +1479,8 @@ static void slave_read(void *opaque) > > > > > > /* Read payload */ > > > do { > > > - size = read(u->slave_fd, &payload, hdr.size); > > > - } while (size < 0 && (errno == EINTR || errno == EAGAIN)); > > > + size = qio_channel_read(ioc, (char *) &payload, hdr.size, NULL); > > > + } while (size == QIO_CHANNEL_ERR_BLOCK); > > > > Same question here. > > This also ends up in qio_channel_socket_readv(). 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 :|