htp: don't assume HTPCallbackRequestLine is the first callback

By assuming that HTPCallbackRequestLine would always be run first,
an memory leak was introduced. It would not check if user data already
existed in the tx, causing it to overwrite the user data pointer is
it already existed.

Bug #1092.

src/app-layer-htp.c

@@ -2032,14 +2032,19 @@ static int HTPCallbackRequestLine(htp_tx_t *tx)
     if (request_uri_normalized == NULL)
         return HTP_OK;
 
-    tx_ud = HTPMalloc(sizeof(*tx_ud));
-    if (unlikely(tx_ud == NULL)) {
-        bstr_free(request_uri_normalized);
-        return HTP_OK;
+    tx_ud = htp_tx_get_user_data(tx);
+    if (likely(tx_ud == NULL)) {
+        tx_ud = HTPMalloc(sizeof(*tx_ud));
+        if (unlikely(tx_ud == NULL)) {
+            bstr_free(request_uri_normalized);
+            return HTP_OK;
+        }
+        memset(tx_ud, 0, sizeof(*tx_ud));
+        htp_tx_set_user_data(tx, tx_ud);
     }
-    memset(tx_ud, 0, sizeof(*tx_ud));
+    if (unlikely(tx_ud->request_uri_normalized != NULL))
+        bstr_free(tx_ud->request_uri_normalized);
     tx_ud->request_uri_normalized = request_uri_normalized;
-    htp_tx_set_user_data(tx, tx_ud);
 
     if (tx->flags) {
         HTPErrorCheckTxRequestFlags(hstate, tx);