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From acb67d9c43f3921861eebbabb447a85644e99320 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Mon, 25 Jul 2016 12:55:36 +0200
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Subject: [PATCH 2/2] virtio: error out if guest exceeds virtqueue size
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
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Message-id: <1469451336-20117-2-git-send-email-stefanha@redhat.com>
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Patchwork-id: 71428
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O-Subject: [virt-devel] [RHEL-7.3 EMBARGOED qemu-kvm PATCH 1/1] virtio: error out if guest exceeds virtqueue size
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Bugzilla: 1359729
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Marc-André Lureau <mlureau@redhat.com>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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A broken or malicious guest can submit more requests than the virtqueue
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size permits.
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The guest can submit requests without bothering to wait for completion
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and is therefore not bound by virtqueue size. This requires reusing
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vring descriptors in more than one request, which is incorrect but
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possible. Processing a request allocates a VirtQueueElement and
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therefore causes unbounded memory allocation controlled by the guest.
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Exit with an error if the guest provides more requests than the
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virtqueue size permits. This bounds memory allocation and makes the
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buggy guest visible to the user.
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This patch fixes CVE-2016-5403.
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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hw/virtio/virtio.c | 5 +++++
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1 file changed, 5 insertions(+)
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diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
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index 132b5af..a861870 100644
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--- a/hw/virtio/virtio.c
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+++ b/hw/virtio/virtio.c
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@@ -452,6 +452,11 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
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max = vq->vring.num;
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+ if (vq->inuse >= max) {
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+ error_report("Virtqueue size exceeded");
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+ exit(1);
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+ }
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+
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i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
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if (vq->vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
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vring_avail_event(vq, vring_avail_idx(vq));
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--
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1.8.3.1
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