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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D9A14CDE008 for ; Fri, 26 Jun 2026 10:34:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wd3sX-0003vk-36; Fri, 26 Jun 2026 06:33:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wd3sV-0003vE-HB for qemu-devel@nongnu.org; Fri, 26 Jun 2026 06:33:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wd3sT-0008HS-HG for qemu-devel@nongnu.org; Fri, 26 Jun 2026 06:33:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782470020; 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=1B932NmTTZIDrWqV5qQ8jWB7HhqdFrxSebezKXALELw=; b=dWUE7p+zUWMSPEEqgpKg2l7oDhAKZKHGuPPjeOOUhEEebNQ4m0gTRLCsuBMNw41z2VFE+X 2JVB0mtYxiXJ+29D1bSZ7OxcOiOBnAlMSHs18h4gi6tOom0B6LraEVo5ZPcdO21GFSJAUT zvieAxU2c62xDQKB2z/TFWg72O/N8n4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-354-zqpfico2P4a6KfJRma8tjA-1; Fri, 26 Jun 2026 06:33:38 -0400 X-MC-Unique: zqpfico2P4a6KfJRma8tjA-1 X-Mimecast-MFC-AGG-ID: zqpfico2P4a6KfJRma8tjA_1782470017 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 175281802674; Fri, 26 Jun 2026 10:33:37 +0000 (UTC) Received: from redhat.com (unknown [10.44.50.5]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 619C8195608A; Fri, 26 Jun 2026 10:33:34 +0000 (UTC) Date: Fri, 26 Jun 2026 11:33:30 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Cc: Mauro Matteo Cascella , Laurent Vivier , qemu-devel@nongnu.org, Paolo Bonzini , Amit Shah , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , qemu-stable@nongnu.org Subject: Re: [PATCH] hw/char/virtio-serial-bus: fix guest-triggerable OOM in control_out() Message-ID: References: <20260622161144.2883799-1-lvivier@redhat.com> <20260626063111-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260626063111-mutt-send-email-mst@kernel.org> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Jun 26, 2026 at 06:32:24AM -0400, Michael S. Tsirkin wrote: > On Fri, Jun 26, 2026 at 10:43:05AM +0100, Daniel P. Berrangé wrote: > > On Thu, Jun 25, 2026 at 06:56:05PM +0200, Mauro Matteo Cascella wrote: > > > On Mon, Jun 22, 2026 at 6:30 PM Daniel P. Berrangé wrote: > > > > > > > > On Mon, Jun 22, 2026 at 06:11:44PM +0200, Laurent Vivier wrote: > > > > > A malicious guest can craft virtqueue descriptors with arbitrary lengths. > > > > > control_out() calls iov_size() on the guest-supplied scatter-gather list > > > > > and passes the result directly to g_malloc(), allowing a guest to force > > > > > QEMU to attempt multi-gigabyte allocations and crash the host process. > > > > > > > > > > Fix this by copying at most sizeof(struct virtio_console_control) into a > > > > > stack-local variable instead of allocating a buffer sized by the guest. > > > > > handle_control_message() only accesses the fixed-size id, event, and > > > > > value fields, so no data beyond the struct was ever needed. > > > > > > > > Does anyone have thoughts on whether we should treat guest initiated > > > > unbounded allocs as a security issue ? > > > > > > > > IIUC, this flaw would require root in the guest OS in order to craft > > > > the malicious virtqueue descriptors. > > > > > > > > A self-initiated crash triggered by root would not historically > > > > be enough justification for CVE. We would require it to be triggered > > > > by unprivileged user. > > > > > > > > Nested virt with device assignment could change that equation though > > > > as the L2 guest could be considered an unpriv user from the L1 POV. > > > > > > > > Also in theory the large alloc might be large enough to consume all > > > > host RAM but not large enough to trigger OOM kill of QEMU. This might > > > > impact operation of other co-located VMs on the same host. > > > > > > > > Anyone think this is bad enough to justify a CVE ? Or should we treat > > > > these OOM scenarios maerely as "hardening" bugs, where they require > > > > 'root' in the L1 guest ? > > > > > > I'd lean toward classifying these as hardening bugs. I don't see the > > > point in assigning Low CVEs to these kinds of issues nowadays. Under > > > current vulnerability management standards, they would definitely be > > > pushed down the priority list and likely skipped or deferred. > > > > Ok, so lets apply as a general rule that all OOM bugs which require > > privileged access in the guest are not assigned CVEs. > > > > An unprivileged guest exploit would be more significant so still > > potentially in scope. > > I'd love to have a document where all this is written up, though. We should add these rules to our main security.rst file in git. where we describe the virt vs non-virt use cases. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|