virtio-net: out-of-bounds buffer write on load

CVE-2013-4149 QEMU 1.3.0 out-of-bounds buffer write in
virtio_net_load()@hw/net/virtio-net.c

>         } else if (n->mac_table.in_use) {
>             uint8_t *buf = g_malloc0(n->mac_table.in_use);

We are allocating buffer of size n->mac_table.in_use

>             qemu_get_buffer(f, buf, n->mac_table.in_use * ETH_ALEN);

and read to the n->mac_table.in_use size buffer n->mac_table.in_use *
ETH_ALEN bytes, corrupting memory.

If adversary controls state then memory written there is controlled
by adversary.
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

hw/net/virtio-net.c

@@ -1362,10 +1362,17 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
         if (n->mac_table.in_use <= MAC_TABLE_ENTRIES) {
             qemu_get_buffer(f, n->mac_table.macs,
                             n->mac_table.in_use * ETH_ALEN);
-        } else if (n->mac_table.in_use) {
-            uint8_t *buf = g_malloc0(n->mac_table.in_use);
-            qemu_get_buffer(f, buf, n->mac_table.in_use * ETH_ALEN);
-            g_free(buf);
+        } else {
+            int64_t i;
+
+            /* Overflow detected - can happen if source has a larger MAC table.
+             * We simply set overflow flag so there's no need to maintain the
+             * table of addresses, discard them all.
+             * Note: 64 bit math to avoid integer overflow.
+             */
+            for (i = 0; i < (int64_t)n->mac_table.in_use * ETH_ALEN; ++i) {
+                qemu_get_byte(f);
+            }
             n->mac_table.multi_overflow = n->mac_table.uni_overflow = 1;
             n->mac_table.in_use = 0;
         }