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 1E209CDB46F for ; Tue, 23 Jun 2026 12:55:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wc0e7-0003Zi-As; Tue, 23 Jun 2026 08:54:31 -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 1wc0e3-0003Yd-FB for qemu-devel@nongnu.org; Tue, 23 Jun 2026 08:54:28 -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 1wc0e1-0007xj-Bj for qemu-devel@nongnu.org; Tue, 23 Jun 2026 08:54:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782219263; 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=J7V9PL7zCAcweGLXmcxQ/fNoFeWh0IqSpwFLRTYBkKw=; b=GkTmx0lRMXwNru2oXR1JjP/BtgG/lY5jy4UxJqDi7oJU/27aEdwgPKCGPVmi2uQnY50JTk //HSza0kwCSpH4ZjQg2T7iUCqs/3QEdELDm3tgWtpReEk6tZ3p/CEOwvd26KcB5rp9tGxU yw0a1XaHgtO07PM7fIh2h3Xz/eBv5ug= 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-112-oRyNwv9uM-eVgZ9WV1JJGw-1; Tue, 23 Jun 2026 08:54:22 -0400 X-MC-Unique: oRyNwv9uM-eVgZ9WV1JJGw-1 X-Mimecast-MFC-AGG-ID: oRyNwv9uM-eVgZ9WV1JJGw_1782219261 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 2AB4F1800370; Tue, 23 Jun 2026 12:54:21 +0000 (UTC) Received: from redhat.com (unknown [10.44.34.133]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E3C5E195604D; Tue, 23 Jun 2026 12:54:17 +0000 (UTC) Date: Tue, 23 Jun 2026 13:54:14 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Cc: Laurent Vivier , qemu-devel@nongnu.org, Mauro Matteo Cascella , 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> <20260623083557-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: <20260623083557-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_H5=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 Tue, Jun 23, 2026 at 08:36:30AM -0400, Michael S. Tsirkin wrote: > On Mon, Jun 22, 2026 at 05:30:33PM +0100, 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. > > Don't see why not. We can treat it as low priority and no embargo. Is there any point in assigning "low" severity CVEs ? I'm not convinced downstream vendors have capacity to deal with "low" CVEs anymore even if we published them. > > > 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 ? > > > > > Cc: qemu-stable@nongnu.org > > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3585 > > > Signed-off-by: Laurent Vivier > > > --- > > > hw/char/virtio-serial-bus.c | 34 +++++++--------------------------- > > > 1 file changed, 7 insertions(+), 27 deletions(-) > > > > > > diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c > > > index cd234dc6db1d..c1973f0248fc 100644 > > > --- a/hw/char/virtio-serial-bus.c > > > +++ b/hw/char/virtio-serial-bus.c > > > @@ -344,22 +344,16 @@ void virtio_serial_throttle_port(VirtIOSerialPort *port, bool throttle) > > > } > > > > > > /* Guest wants to notify us of some event */ > > > -static void handle_control_message(VirtIOSerial *vser, void *buf, size_t len) > > > +static void handle_control_message(VirtIOSerial *vser, > > > + struct virtio_console_control *gcpkt) > > > { > > > VirtIODevice *vdev = VIRTIO_DEVICE(vser); > > > struct VirtIOSerialPort *port; > > > VirtIOSerialPortClass *vsc; > > > - struct virtio_console_control cpkt, *gcpkt; > > > + struct virtio_console_control cpkt; > > > uint8_t *buffer; > > > size_t buffer_len; > > > > > > - gcpkt = buf; > > > - > > > - if (len < sizeof(cpkt)) { > > > - /* The guest sent an invalid control packet */ > > > - return; > > > - } > > > - > > > cpkt.event = virtio_lduw_p(vdev, &gcpkt->event); > > > cpkt.value = virtio_lduw_p(vdev, &gcpkt->value); > > > > > > @@ -457,41 +451,27 @@ static void control_in(VirtIODevice *vdev, VirtQueue *vq) > > > > > > static void control_out(VirtIODevice *vdev, VirtQueue *vq) > > > { > > > + struct virtio_console_control cpkt; > > > VirtQueueElement *elem; > > > VirtIOSerial *vser; > > > - uint8_t *buf; > > > size_t len; > > > > > > vser = VIRTIO_SERIAL(vdev); > > > > > > - len = 0; > > > - buf = NULL; > > > for (;;) { > > > - size_t cur_len; > > > - > > > elem = virtqueue_pop(vq, sizeof(VirtQueueElement)); > > > if (!elem) { > > > break; > > > } > > > > > > - cur_len = iov_size(elem->out_sg, elem->out_num); > > > - /* > > > - * Allocate a new buf only if we didn't have one previously or > > > - * if the size of the buf differs > > > - */ > > > - if (cur_len > len) { > > > - g_free(buf); > > > - > > > - buf = g_malloc(cur_len); > > > - len = cur_len; > > > + len = iov_to_buf(elem->out_sg, elem->out_num, 0, &cpkt, sizeof(cpkt)); > > > + if (len == sizeof(cpkt)) { > > > + handle_control_message(vser, &cpkt); > > > } > > > - iov_to_buf(elem->out_sg, elem->out_num, 0, buf, cur_len); > > > > > > - handle_control_message(vser, buf, cur_len); > > > virtqueue_push(vq, elem, 0); > > > g_free(elem); > > > } > > > - g_free(buf); > > > virtio_notify(vdev, vq); > > > } > > > > > > -- > > > 2.54.0 > > > > > > > > > > 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 :| > 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 :|