net/colo-compare.c: Fix memory leak and code style issue.

This patch to fix the origin "char *data" memory leak, code style issue
and add necessary check here.
Reported-by: Coverity (CID 1402785)

Signed-off-by: Zhang Chen <chen.zhang@intel.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/colo-compare.c

@@ -127,6 +127,17 @@ static int compare_chr_send(CompareState *s,
                             uint32_t vnet_hdr_len,
                             bool notify_remote_frame);
 
+static bool packet_matches_str(const char *str,
+                               const uint8_t *buf,
+                               uint32_t packet_len)
+{
+    if (packet_len != strlen(str)) {
+        return false;
+    }
+
+    return !memcmp(str, buf, strlen(str));
+}
+
 static void notify_remote_frame(CompareState *s)
 {
     char msg[] = "DO_CHECKPOINT";
@@ -1008,21 +1019,23 @@ static void compare_notify_rs_finalize(SocketReadState *notify_rs)
 {
     CompareState *s = container_of(notify_rs, CompareState, notify_rs);
 
-    /* Get Xen colo-frame's notify and handle the message */
-    char *data = g_memdup(notify_rs->buf, notify_rs->packet_len);
-    char msg[] = "COLO_COMPARE_GET_XEN_INIT";
+    const char msg[] = "COLO_COMPARE_GET_XEN_INIT";
     int ret;
 
-    if (!strcmp(data, "COLO_USERSPACE_PROXY_INIT")) {
+    if (packet_matches_str("COLO_USERSPACE_PROXY_INIT",
+                           notify_rs->buf,
+                           notify_rs->packet_len)) {
         ret = compare_chr_send(s, (uint8_t *)msg, strlen(msg), 0, true);
         if (ret < 0) {
             error_report("Notify Xen COLO-frame INIT failed");
         }
-    }
-
-    if (!strcmp(data, "COLO_CHECKPOINT")) {
+    } else if (packet_matches_str("COLO_CHECKPOINT",
+                                  notify_rs->buf,
+                                  notify_rs->packet_len)) {
         /* colo-compare do checkpoint, flush pri packet and remove sec packet */
         g_queue_foreach(&s->conn_list, colo_flush_packets, s);
+    } else {
+        error_report("COLO compare got unsupported instruction");
     }
 }