ovsdb-server: Fix schema leak while reading db.

parse_txn() function doesn't always take ownership of the 'schema'
passed.  So, if the schema of the clustered db has same version as the
one that already in use, parse_txn() will not use it, resulting with a
memory leak:

 7,827 (56 direct, 7,771 indirect) bytes in 1 blocks are definitely lost
    at 0x483BB1A: calloc (vg_replace_malloc.c:762)
    by 0x44AD02: xcalloc (util.c:121)
    by 0x40E70E: ovsdb_schema_create (ovsdb.c:41)
    by 0x40EA6D: ovsdb_schema_from_json (ovsdb.c:217)
    by 0x415EDD: ovsdb_storage_read (storage.c:280)
    by 0x408968: read_db (ovsdb-server.c:607)
    by 0x40733D: main_loop (ovsdb-server.c:227)
    by 0x40733D: main (ovsdb-server.c:469)

While we could put ovsdb_schema_destroy() in a few places inside
'parse_txn()', from the users' point of view it seems better to have a
constant argument and just clone the 'schema' if needed.  The caller
will be responsible for destroying the 'schema' it owns.

Fixes: 1b1d2e6 ("ovsdb: Introduce experimental support for clustered databases.")
Acked-by: Han Zhou <[email protected]>
Signed-off-by: Ilya Maximets <[email protected]>

ovsdb/ovsdb-server.c

@@ -540,7 +540,7 @@ close_db(struct server_config *config, struct db *db, char *comment)
 
 static struct ovsdb_error * OVS_WARN_UNUSED_RESULT
 parse_txn(struct server_config *config, struct db *db,
-          struct ovsdb_schema *schema, const struct json *txn_json,
+          const struct ovsdb_schema *schema, const struct json *txn_json,
           const struct uuid *txnid)
 {
     if (schema && (!db->db->schema || strcmp(schema->version,
@@ -565,7 +565,7 @@ parse_txn(struct server_config *config, struct db *db,
              ? xasprintf("database %s schema changed", db->db->name)
              : xasprintf("database %s connected to storage", db->db->name)));
 
-        ovsdb_replace(db->db, ovsdb_create(schema, NULL));
+        ovsdb_replace(db->db, ovsdb_create(ovsdb_schema_clone(schema), NULL));
 
         /* Force update to schema in _Server database. */
         db->row_uuid = UUID_ZERO;
@@ -614,6 +614,7 @@ read_db(struct server_config *config, struct db *db)
         } else {
             error = parse_txn(config, db, schema, txn_json, &txnid);
             json_destroy(txn_json);
+            ovsdb_schema_destroy(schema);
             if (error) {
                 break;
             }