lib/vector/Vlib: Fix out-of-scope memory access (#4667)

A local array was used to store column name and column
type for each column, and a pointer to this local array
was stored and accessed outside its scope, which can cause
undefined behavior.

To avoid this, use memory from heap to store this information
so that it's accessible outside where its defined and free
this memory at the end to avoid memory leaks.

This was found using cppcheck tool.

Signed-off-by: Mohan Yelugoti <[email protected]>

lib/vector/Vlib/dbcolumns.c

@@ -154,7 +154,7 @@ const char *Vect_get_column_names_types(struct Map_info *Map, int field)
     dbHandle handle;
     dbString table_name;
     dbTable *table;
-    const char **col_type_names;
+    char **col_type_names;
     char *list;
 
     num_dblinks = Vect_get_num_dblinks(Map);
@@ -180,16 +180,21 @@ const char *Vect_get_column_names_types(struct Map_info *Map, int field)
     ncols = db_get_table_number_of_columns(table);
     col_type_names = G_malloc(ncols * sizeof(char *));
     for (col = 0; col < ncols; col++) {
-        char buf[256];
+        col_type_names[col] = (char *)G_calloc(256, sizeof(char));
 
-        sprintf(buf, "%s(%s)",
+        sprintf(col_type_names[col], "%s(%s)",
                 db_get_column_name(db_get_table_column(table, col)),
                 db_sqltype_name(
                     db_get_column_sqltype(db_get_table_column(table, col))));
-        col_type_names[col] = buf;
     }
-    if ((list = G_str_concat(col_type_names, ncols, ",", BUFF_MAX)) == NULL)
+
+    if ((list = G_str_concat((const char **)col_type_names, ncols, ",",
+                             BUFF_MAX)) == NULL)
         list = G_store("");
+
+    for (col = 0; col < ncols; col++) {
+        G_free(col_type_names[col]);
+    }
     G_free(col_type_names);
     G_debug(3, "%s", list);