From: P J P Date: Tue, 26 Jul 2016 14:31:59 +0000 (+0100) Subject: virtio: error out if guest exceeds virtqueue size X-Git-Tag: xen-4.8.0-rc1^0 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=c4e0d84d3c92923fdbc7fa922638d54e5e834753;p=qemu-xen-traditional.git virtio: error out if guest exceeds virtqueue size A broken or malicious guest can submit more requests than the virtqueue size permits. The guest can submit requests without bothering to wait for completion and is therefore not bound by virtqueue size. This requires reusing vring descriptors in more than one request, which is incorrect but possible. Processing a request allocates a VirtQueueElement and therefore causes unbounded memory allocation controlled by the guest. Exit with an error if the guest provides more requests than the virtqueue size permits. This bounds memory allocation and makes the buggy guest visible to the user. Reported-by: Zhenhao Hong Signed-off-by: Stefan Hajnoczi --- diff --git a/hw/virtio.c b/hw/virtio.c index c26feffc..42897bfe 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -421,6 +421,11 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem) /* When we start there are none of either input nor output. */ elem->out_num = elem->in_num = 0; + if (vq->inuse >= vq->vring.num) { + fprintf(stderr, "Virtqueue size exceeded"); + exit(1); + } + i = head = virtqueue_get_head(vq, vq->last_avail_idx++); do { struct iovec *sg;