MDEV-17065 Crash on SHOW CREATE TABLE with CHECK CONSTRAINT

The problem was that the original alias was replaced with a new allocated
string, but constraint item's are still pointing to the original alias.

Fixed by storing the original alias used when printing constraint in the
tables mem_root.

mysql-test/r/constraints.result

@@ -74,3 +74,40 @@ CREATE TABLE t_illegal (col_1 INT CHECK something (whatever));
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'something (whatever))' at line 1
 CREATE TABLE t_illegal (col_1 INT CHECK something);
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'something)' at line 1
+CREATE TABLE long_enough_name (
+pk int(11) NOT NULL,
+f1 int(11) DEFAULT NULL,
+f2 int(11) NOT NULL,
+f3 int(11) DEFAULT NULL,
+f4 timestamp NOT NULL DEFAULT current_timestamp(),
+f5 varchar(32) COLLATE utf8_bin NOT NULL DEFAULT 'foo',
+f6 smallint(6) NOT NULL DEFAULT 1,
+f7 int(11) DEFAULT NULL,
+PRIMARY KEY (pk),
+KEY idx1 (f7),
+KEY idx2 (f1),
+KEY idx3 (f2),
+KEY idx4 (f3),
+CONSTRAINT constr CHECK (f6 >= 0)
+);
+SELECT * FROM long_enough_name AS tbl;
+pk	f1	f2	f3	f4	f5	f6	f7
+SHOW CREATE TABLE long_enough_name;
+Table	Create Table
+long_enough_name	CREATE TABLE `long_enough_name` (
+  `pk` int(11) NOT NULL,
+  `f1` int(11) DEFAULT NULL,
+  `f2` int(11) NOT NULL,
+  `f3` int(11) DEFAULT NULL,
+  `f4` timestamp NOT NULL DEFAULT current_timestamp(),
+  `f5` varchar(32) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL DEFAULT 'foo',
+  `f6` smallint(6) NOT NULL DEFAULT 1,
+  `f7` int(11) DEFAULT NULL,
+  PRIMARY KEY (`pk`),
+  KEY `idx1` (`f7`),
+  KEY `idx2` (`f1`),
+  KEY `idx3` (`f2`),
+  KEY `idx4` (`f3`),
+  CONSTRAINT `constr` CHECK (`f6` >= 0)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE long_enough_name;

mysql-test/t/constraints.test

@@ -77,3 +77,28 @@ CREATE TABLE t_illegal (col_1 INT CHECK something (whatever));
 --error ER_PARSE_ERROR
 CREATE TABLE t_illegal (col_1 INT CHECK something);
 
+#
+# MDEV-17065 Crash on SHOW CREATE TABLE with CHECK CONSTRAINT
+#
+
+CREATE TABLE long_enough_name (
+pk int(11) NOT NULL,
+f1 int(11) DEFAULT NULL,
+f2 int(11) NOT NULL,
+f3 int(11) DEFAULT NULL,
+f4 timestamp NOT NULL DEFAULT current_timestamp(),
+f5 varchar(32) COLLATE utf8_bin NOT NULL DEFAULT 'foo',
+f6 smallint(6) NOT NULL DEFAULT 1,
+f7 int(11) DEFAULT NULL,
+PRIMARY KEY (pk),
+KEY idx1 (f7),
+KEY idx2 (f1),
+KEY idx3 (f2),
+KEY idx4 (f3),
+CONSTRAINT constr CHECK (f6 >= 0)
+);
+ 
+SELECT * FROM long_enough_name AS tbl;
+SHOW CREATE TABLE long_enough_name;
+ 
+DROP TABLE long_enough_name;

sql/table.cc

@@ -3007,6 +3007,8 @@ enum open_frm_error open_table_from_share(THD *thd, TABLE_SHARE *share,
 {
   enum open_frm_error error;
   uint records, i, bitmap_size, bitmap_count;
+  size_t tmp_length;
+  const char *tmp_alias;
   bool error_reported= FALSE;
   uchar *record, *bitmaps;
   Field **field_ptr;
@@ -3033,8 +3035,15 @@ enum open_frm_error open_table_from_share(THD *thd, TABLE_SHARE *share,
   }
   init_sql_alloc(&outparam->mem_root, TABLE_ALLOC_BLOCK_SIZE, 0, MYF(0));
 
-  if (outparam->alias.copy(alias, strlen(alias), table_alias_charset))
+  /*
+    We have to store the original alias in mem_root as constraints and virtual
+    functions may store pointers to it
+  */
+  tmp_length= strlen(alias);
+  if (!(tmp_alias= strmake_root(&outparam->mem_root, alias, tmp_length)))
     goto err;
+
+  outparam->alias.set(tmp_alias, tmp_length, table_alias_charset);
   outparam->quick_keys.init();
   outparam->covering_keys.init();
   outparam->intersect_keys.init();
@@ -4487,7 +4496,7 @@ void TABLE::init(THD *thd, TABLE_LIST *tl)
                                    s->table_name.str,
                                    tl->alias);
   /* Fix alias if table name changes. */
-  if (strcmp(alias.c_ptr(), tl->alias))
+  if (!alias.alloced_length() || strcmp(alias.c_ptr(), tl->alias))
     alias.copy(tl->alias, strlen(tl->alias), alias.charset());
 
   tablenr= thd->current_tablenr++;