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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 3613FC433DF for ; Mon, 15 Jun 2020 20:40:48 +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 EEDF82078E for ; Mon, 15 Jun 2020 20:40:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Yfad/GZb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EEDF82078E 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]:35118 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jkvuR-0002Wb-4T for qemu-devel@archiver.kernel.org; Mon, 15 Jun 2020 16:40:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:32902) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jkvtF-0001Gu-8x for qemu-devel@nongnu.org; Mon, 15 Jun 2020 16:39:33 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:42517 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jkvtD-0000ID-KN for qemu-devel@nongnu.org; Mon, 15 Jun 2020 16:39:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592253570; h=from:from: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=xYc7zBg925iLLXxuMTQkUX7GD3ahgBpuRJARONIQ9t4=; b=Yfad/GZbtkAOd1U5USYksrLzNJeY68BtaQ4oRE6ZzhrB/at+G+No1eMXZrgDA7XFeY6ACF T+v/nbX3b4VymiK0Zwm6bxHmgnHtY4072K7+K4UPh5QOsMh882zhScpix+zJdaNk0b6zEc M3kMQ8F/w1eHSG3YgBzzkNYlq1mb/r0= 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-50-28st6aurPRqF30I_xOYjWA-1; Mon, 15 Jun 2020 16:39:29 -0400 X-MC-Unique: 28st6aurPRqF30I_xOYjWA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 20C73803303; Mon, 15 Jun 2020 20:39:28 +0000 (UTC) Received: from [10.3.112.27] (ovpn-112-27.phx2.redhat.com [10.3.112.27]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 894DE5C1D2; Mon, 15 Jun 2020 20:39:27 +0000 (UTC) Subject: Re: [PATCH v2 2/2] block: Call attention to truncation of long NBD exports From: Eric Blake To: qemu-devel@nongnu.org References: <20200610163741.3745251-1-eblake@redhat.com> <20200610163741.3745251-3-eblake@redhat.com> Organization: Red Hat, Inc. Message-ID: <9b324e3e-8758-f8d9-7acc-50f118b289b4@redhat.com> Date: Mon, 15 Jun 2020 15:39:27 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200610163741.3745251-3-eblake@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/15 16:38:57 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: , Cc: Kevin Wolf , vsementsov@virtuozzo.com, qemu-block@nongnu.org, xuwei@redhat.com, qemu-stable@nongnu.org, Max Reitz , ppandit@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/10/20 11:37 AM, Eric Blake wrote: > Commit 93676c88 relaxed our NBD client code to request export names up > to the NBD protocol maximum of 4096 bytes without NUL terminator, even > though the block layer can't store anything longer than 4096 bytes > including NUL terminator for display to the user. Since this means > there are some export names where we have to truncate things, we can > at least try to make the truncation a bit more obvious for the user. > Note that in spite of the truncated display name, we can still > communicate with an NBD server using such a long export name; this was > deemed nicer than refusing to even connect to such a server (since the > server may not be under our control, and since determining our actual > length limits gets tricky when nbd://host:port/export and > nbd+unix:///export?socket=/path are themselves variable-length > expansions beyond the export name but count towards the block layer > name length). > > +++ b/block/nbd.c > } else if (host && !s->export) { > - snprintf(bs->exact_filename, sizeof(bs->exact_filename), > - "nbd://%s:%s", host, port); > + len = snprintf(bs->exact_filename, sizeof(bs->exact_filename), > + "nbd://%s:%s", host, port); > + } > + if (len > sizeof(bs->exact_filename)) { Max pointed out off-list that this is off-by-one: by not using >=, I am failing to detect overflow when exactly one byte is truncated. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org