net/colo.c: Fix the pointer issue reported by Coverity.

When enabled 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 needs 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.zhang@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/colo.c

@@ -44,21 +44,28 @@ 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, "
-                                        "pkt->vnet_hdr_len", pkt->vnet_hdr_len);
+    assert(data);
+
+    /* Check the received vnet_hdr_len then add the offset */
+    if ((pkt->vnet_hdr_len > sizeof(struct virtio_net_hdr_v1_hash)) ||
+        (pkt->size < sizeof(struct eth_header) + sizeof(struct vlan_header) +
+        pkt->vnet_hdr_len)) {
+        /*
+         * The received remote packet maybe misconfiguration here,
+         * Please enable/disable filter module's the vnet_hdr flag at
+         * the same time.
+         */
+        trace_colo_proxy_main_vnet_info("This received packet load wrong ",
+                                        pkt->vnet_hdr_len, pkt->size);
         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.

net/colo.h

@@ -18,6 +18,7 @@
 #include "qemu/jhash.h"
 #include "qemu/timer.h"
 #include "net/eth.h"
+#include "standard-headers/linux/virtio_net.h"
 
 #define HASHTABLE_MAX_SIZE 16384
 

net/trace-events

@@ -9,7 +9,7 @@ vhost_user_event(const char *chr, int event) "chr: %s got event: %d"
 
 # colo.c
 colo_proxy_main(const char *chr) ": %s"
-colo_proxy_main_vnet_info(const char *sta, int size) ": %s = %d"
+colo_proxy_main_vnet_info(const char *sta, uint32_t vnet_hdr, int size) ": %s pkt->vnet_hdr_len = %u, pkt->size = %d"
 
 # colo-compare.c
 colo_compare_main(const char *chr) ": %s"