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>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index a0fa5de210cf..026be580d318 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -532,6 +532,12 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
         *iovcount = seg;
         if (unlikely(log))
                 *log_num = nlogs;
+
+        /* Detect overrun */
+        if (unlikely(datalen > 0)) {
+                r = UIO_MAXIOV + 1;
+                goto err;
+        }
         return headcount;
 err:
         vhost_discard_vq_desc(vq, headcount);
@@ -587,6 +593,14 @@ static void handle_rx(struct vhost_net *net)
                 /* On error, stop handling until the next kick. */
                 if (unlikely(headcount < 0))
                         break;
+                /* On overrun, truncate and discard */
+                if (unlikely(headcount > UIO_MAXIOV)) {
+                        msg.msg_iovlen = 1;
+                        err = sock->ops->recvmsg(NULL, sock, &msg,
+                                                 1, MSG_DONTWAIT | MSG_TRUNC);
+                        pr_debug("Discarded rx packet: len %zd\n", sock_len);
+                        continue;
+                }
                 /* OK, now we need to know about added descriptors. */
                 if (!headcount) {
                         if (unlikely(vhost_enable_notify(&net->dev, vq))) {