Fix for MXS-968

This commit adds a free() to null_auth_free_client_data, which plugs
the memory leak in maxinfo.

Also, this commit fixes some segfaults when multiple threads are
running status_row() or variable_row(). The functions use
statically allocated index variables, which often go out-of-bounds
in concurrent use. This fix changes the indexes to thread-specific
variables, with allocating and deallocating. This does seem to slow
the functions down somewhat.

server/modules/authenticator/null_auth.c

@@ -150,4 +150,8 @@ null_auth_is_client_ssl_capable(DCB *dcb)
  * @param dcb Request handler DCB connected to the client
  */
 static void
-null_auth_free_client_data(DCB *dcb) {}
+null_auth_free_client_data(DCB *dcb)
+{
+    free(dcb->data);
+    dcb->data = NULL;
+}

server/modules/routing/maxinfo/maxinfo_exec.c

@@ -825,7 +825,6 @@ typedef struct
     int index;
     char    *like;
 } VARCONTEXT;
-
 /**
  * Callback function to populate rows of the show variable
  * command
@@ -836,7 +835,7 @@ typedef struct
 static RESULT_ROW *
 variable_row(RESULTSET *result, void *data)
 {
-    VARCONTEXT  *context = (VARCONTEXT *)data;
+    VARCONTEXT *context = (VARCONTEXT *) data;
     RESULT_ROW *row;
     char buf[80];
 
@@ -862,10 +861,14 @@ variable_row(RESULTSET *result, void *data)
                          (long)(*variables[context->index].func)());
                 resultset_row_set(row, 1, buf);
                 break;
+            default:
+                ss_dassert(!true);
         }
         context->index++;
         return row;
     }
+    // We only get to this point once all variables have been printed
+    free(data);
     return NULL;
 }
 
@@ -911,15 +914,19 @@ RESULTSET *
 maxinfo_variables()
 {
     RESULTSET *result;
-    static VARCONTEXT   context;
+    VARCONTEXT *context;
-
+    if ((context = malloc(sizeof(VARCONTEXT))) == NULL)
-    context.like = NULL;
-    context.index = 0;
-
-    if ((result = resultset_create(variable_row, &context)) == NULL)
     {
         return NULL;
     }
+    context->like = NULL;
+    context->index = 0;
+
+    if ((result = resultset_create(variable_row, context)) == NULL)
+    {
+        free(context);
+        return NULL;
+    }
     resultset_add_column(result, "Variable_name", 40, COL_TYPE_VARCHAR);
     resultset_add_column(result, "Value", 40, COL_TYPE_VARCHAR);
     return result;
@@ -1140,10 +1147,14 @@ status_row(RESULTSET *result, void *data)
                          (long)(*status[context->index].func)());
                 resultset_row_set(row, 1, buf);
                 break;
+            default:
+                ss_dassert(!true);
         }
         context->index++;
         return row;
     }
+    // We only get to this point once all status elements have been printed
+    free(data);
     return NULL;
 }
 
@@ -1189,15 +1200,19 @@ RESULTSET *
 maxinfo_status()
 {
     RESULTSET   *result;
-    static VARCONTEXT   context;
+    VARCONTEXT   *context;
-
+    if ((context = malloc(sizeof(VARCONTEXT))) == NULL)
-    context.like = NULL;
-    context.index = 0;
-
-    if ((result = resultset_create(status_row, &context)) == NULL)
     {
         return NULL;
     }
+    context->like = NULL;
+    context->index = 0;
+
+    if ((result = resultset_create(status_row, context)) == NULL)
+    {
+        free(context);
+        return NULL;
+    }
     resultset_add_column(result, "Variable_name", 40, COL_TYPE_VARCHAR);
     resultset_add_column(result, "Value", 40, COL_TYPE_VARCHAR);
     return result;