[PATCH V2] net/colo.c: Fix the pointer issuse reported by Coverity.

[Zhang Chen]

When enable the virtio-net-pci, guest network packet will
load the vnet_hdr. In COLO status, the primary VM's network
packet maybe redirect to another VM, it need filter-redirect
enable the vnet_hdr flag at the same time, COLO-proxy will
correctly parse the original network packet. If have any
misconfiguration here, the vnet_hdr_len is wrong for parse
the packet, the data+offset will point to wrong place.

Signed-off-by: Zhang Chen <chen.zh...@intel.com>
---
 net/colo.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/colo.c b/net/colo.c
index 6b0ff562ad..524afa3d9b 100644
--- a/net/colo.c
+++ b/net/colo.c
@@ -44,21 +44,22 @@ int parse_packet_early(Packet *pkt)
 {
     int network_length;
     static const uint8_t vlan[] = {0x81, 0x00};
-    uint8_t *data = pkt->data + pkt->vnet_hdr_len;
+    uint8_t *data = pkt->data;
     uint16_t l3_proto;
     ssize_t l2hdr_len;
 
-    if (data == NULL) {
-        trace_colo_proxy_main_vnet_info("This packet is not parsed correctly, "
+    assert(data);
+
+    /* Check the received vnet_hdr_len then add the offset */
+    if (pkt->size < sizeof(struct eth_header) + sizeof(struct vlan_header)
+        + pkt->vnet_hdr_len) {
+        trace_colo_proxy_main_vnet_info("This packet may be load wrong "
                                         "pkt->vnet_hdr_len", 
pkt->vnet_hdr_len);
         return 1;
     }
-    l2hdr_len = eth_get_l2_hdr_length(data);
+    data += pkt->vnet_hdr_len;
 
-    if (pkt->size < ETH_HLEN + pkt->vnet_hdr_len) {
-        trace_colo_proxy_main("pkt->size < ETH_HLEN");
-        return 1;
-    }
+    l2hdr_len = eth_get_l2_hdr_length(data);
 
     /*
      * TODO: support vlan.
-- 
2.25.1