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 BDD94CDB46F for ; Tue, 23 Jun 2026 12:37:14 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wc0Mv-0001V5-Jm; Tue, 23 Jun 2026 08:36:45 -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 1wc0Mr-0001Py-GM for qemu-devel@nongnu.org; Tue, 23 Jun 2026 08:36:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wc0Mp-0004mj-3W for qemu-devel@nongnu.org; Tue, 23 Jun 2026 08:36:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782218196; 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=cHte1D/PIxAbtMivvHxIFjT0xiyLpH/zlQ+pJoXe6CM=; b=PUWsqTBYrD6p9Ke1EE01VTDDm872fj6wJzRris9oEHhqCoWDrxp1f9WZtMV1CwhHR7r17D +XDfpj9cvJsOaPR1hOEY+DJq1JlsHPAhrlJ8dml4VgV6uaZ6LvmZzKY+G6YPYC91Z2cckp TCDYNO6Dbx8tJDihLHmeXU+32ptUIzs= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-509-TLIY_ro5OSeVRsV2kvjmDA-1; Tue, 23 Jun 2026 08:36:35 -0400 X-MC-Unique: TLIY_ro5OSeVRsV2kvjmDA-1 X-Mimecast-MFC-AGG-ID: TLIY_ro5OSeVRsV2kvjmDA_1782218194 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-49221de4ed4so37414415e9.0 for ; Tue, 23 Jun 2026 05:36:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1782218194; x=1782822994; darn=nongnu.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=cHte1D/PIxAbtMivvHxIFjT0xiyLpH/zlQ+pJoXe6CM=; b=cQq3bu74uB1wwtB/UTsg79hTVN4AulgoEtF25rySgikw2JnIodQgg3eC2AQpv7V8o+ 2x/eYlGhHH6gL58iTtJYUynGlZnjGXlxPmz1fKybUaBE6Zp9/k9nqaPvrCaswTJY38qx 7vmOpA1DCNVibLuiu86brs8J+7bDk6vg2cMy5yjYI4jlcsFouyTOYbybZNivW+CkpgmT FFGtAAv8lRj81dCIm9DUIJ1enJWVc0xbA5Y6oSBupn8dbqWuy7zAx9KihaBNkR00yXVK KJd27aQJO4mQgBtldG5TknGK9YqxuDZFTb9UNKkme6S9QDR5mk50UStQK935PSqM9kV5 WHEg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782218194; x=1782822994; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=cHte1D/PIxAbtMivvHxIFjT0xiyLpH/zlQ+pJoXe6CM=; b=q0JfmxNw3ktpeJvNtypPafW+upO/yTUEOGoR4+LEVRE6O6tmHu4eiW7yRa/TTP/V2p MYdYP2vgXrbHBl6/bMqqjTFH9BYwWID05mJlVnjXa2OFFjuaCB3AisKr5XojAJHlumCr jU5CcAyXPcByz1SJsUt+UH3Xe808fkrajTtLqVl0rAMi6rCMwbZdBKwYxCGZH0Ru/dEy wqOhDUx9tyMscHAnAlLBuFTBwjKYfxNzBRJjsbdRKwt433ObOB+6eEP27Tu8Q6+8XkVq tWOKQgHyJpnIS1BTXtZlzflk2PcouHDgzZNiYK3BPFHZasWaEbEypGYKILCZw1FoTkZ3 fk+w== X-Forwarded-Encrypted: i=1; AFNElJ+M/OA5sbnKE69X5j+Hy9IfYsw8+SzZ/dSKUYr99JIduICWM2rFlrVH6etMFer5GpV2rruhWuZgAWd/@nongnu.org X-Gm-Message-State: AOJu0YyWor++tHuhEFQXsMGAmYHRPNEf3BQO0Qpb6WRImnlYTlLkrBcQ FTxZXeeQ2ygtmU0epq4YvIZxk/Wixd6k4gXiiDA9Cq8glMAlvRLMdGxxUuWnC/m2i9qw2Myb3aW lKo9+qpdbyH6NLnhaGhu/CVUrjdrjUx8dfBVDMbCRPnXdN64ggFvGLouP X-Gm-Gg: AfdE7clD92HqzpjZ3Z2kSCyg5UGZuocJ95+dIPJNUlXIVkynAqo5YzFIY9yQ2omNsvJ cd7cAECVFJEhBDKCMhVT3TaB7aVx5rcshylHRRKb5RrKesRI4MZq6D1uBu/98kTi4ThCPKhYFMh WjtMF1JwP6BG7tdxDm1NGmDzAdWekk7VPz5seA4Sow7TGxZmSLW/kMp5llLSZTeMx46kZWWxa/z NmXX5essC83+pufywm0u1yP4wooLs8nHBgaE6p9ih7rBKOHL1IEeWg5oRbaXh7detn2MSIBIRoU HzTucweFyWAT1Ur6KNVqyBjeQJy3akoMZGyo5tb+yE5HaOMtERMFVprxtyZ/cVLGwV5uevbnInf z9NISZWp6iYSgFcaKKWI14A1MYlCK8BUc X-Received: by 2002:a05:600d:8496:20b0:490:e180:2ed with SMTP id 5b1f17b1804b1-49240e20c76mr216180085e9.4.1782218194137; Tue, 23 Jun 2026 05:36:34 -0700 (PDT) X-Received: by 2002:a05:600d:8496:20b0:490:e180:2ed with SMTP id 5b1f17b1804b1-49240e20c76mr216179455e9.4.1782218193606; Tue, 23 Jun 2026 05:36:33 -0700 (PDT) Received: from redhat.com (IGLD-80-230-85-71.inter.net.il. [80.230.85.71]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4923fd30078sm373505035e9.7.2026.06.23.05.36.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jun 2026 05:36:33 -0700 (PDT) Date: Tue, 23 Jun 2026 08:36:30 -0400 From: "Michael S. Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Laurent Vivier , qemu-devel@nongnu.org, Mauro Matteo Cascella , Paolo Bonzini , Amit Shah , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , qemu-stable@nongnu.org Subject: Re: [PATCH] hw/char/virtio-serial-bus: fix guest-triggerable OOM in control_out() Message-ID: <20260623083557-mutt-send-email-mst@kernel.org> References: <20260622161144.2883799-1-lvivier@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org 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. > 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 :|