Code: static int get_rx_bufs(struct vhost_virtqueue *vq,
		       struct vring_used_elem *heads,
		       int datalen,
		       unsigned *iovcount,
		       struct vhost_log *log,
		       unsigned *log_num,
		       unsigned int quota)
{
	unsigned int out, in;
	int seg = 0;
	int headcount = 0;
	unsigned d;
	int r, nlogs = 0;

	while (datalen > 0 && headcount < quota) {
		if (unlikely(seg >= UIO_MAXIOV)) {
			r = -ENOBUFS;
			goto err;
		}
		d = vhost_get_vq_desc(vq->dev, vq, vq->iov + seg,
				      ARRAY_SIZE(vq->iov) - seg, &out,
				      &in, log, log_num);
		if (d == vq->num) {
			r = 0;
			goto err;
		}
		if (unlikely(out || in <= 0)) {
			vq_err(vq, "unexpected descriptor format for RX: "
				"out %d, in %d\n", out, in);
			r = -EINVAL;
			goto err;
		}
		if (unlikely(log)) {
			nlogs += *log_num;
			log += *log_num;
		}
		heads[headcount].id = d;
		heads[headcount].len = iov_length(vq->iov + seg, in);
		datalen -= heads[headcount].len;
		++headcount;
		seg += in;
	}
	heads[headcount - 1].len += datalen;
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
 	return headcount;
 err:
 	vhost_discard_vq_desc(vq, headcount);
	return r;
}

Vulnerability Type: DoS +Priv Mem. Corr. 
CWE ID: CWE-20
Summary: drivers/vhost/net.c in the Linux kernel before 3.13.10, when mergeable buffers are disabled, does not properly validate packet lengths, which allows guest OS users to cause a denial of service (memory corruption and host OS crash) or possibly gain privileges on the host OS via crafted packets, related to the handle_rx and get_rx_bufs functions.
Commit Message: vhost: fix total length when packets are too short

When mergeable buffers are disabled, and the
incoming packet is too large for the rx buffer,
get_rx_bufs returns success.

This was intentional in order for make recvmsg
truncate the packet and then handle_rx would
detect err != sock_len and drop it.

Unfortunately we pass the original sock_len to
recvmsg - which means we use parts of iov not fully
validated.

Fix this up by detecting this overrun and doing packet drop
immediately.

CVE-2014-0077

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>