MDEV-38830: SIGSEGV and UBSAN null-pointer-use in TABLE::evaluate_upd…

mysql-test/main/temp_table.result

@@ -746,3 +746,14 @@ SELECT * FROM tmp_38716_2 where b=20;
 a	b	c
 NULL	20	21
 DROP TABLE tmp_38716_2;
+#
+# MDEV-38830
+#
+CREATE TEMPORARY TABLE tmp_38830 (c INT KEY);
+INSERT INTO tmp_38830 VALUES (1);
+ALTER TABLE tmp_38830 ADD COLUMN (d TIMESTAMP ON UPDATE CURRENT_TIMESTAMP);
+UPDATE tmp_38830 SET c=c+1;
+select * from tmp_38830;
+c	d
+2	2001-01-01 10:20:30
+DROP TEMPORARY TABLE tmp_38830;

mysql-test/main/temp_table.test

@@ -810,3 +810,15 @@ INSERT INTO tmp_38716_2 (b) VALUES (20);
 SELECT * FROM tmp_38716_2 where b=20;
 
 DROP TABLE tmp_38716_2;
+
+
+--echo #
+--echo # MDEV-38830
+--echo #
+CREATE TEMPORARY TABLE tmp_38830 (c INT KEY);
+INSERT INTO tmp_38830 VALUES (1);
+ALTER TABLE tmp_38830 ADD COLUMN (d TIMESTAMP ON UPDATE CURRENT_TIMESTAMP);
+UPDATE tmp_38830 SET c=c+1;
+select * from tmp_38830;
+
+DROP TEMPORARY TABLE tmp_38830;

mysql-test/suite/maria/alter.result

@@ -63,7 +63,7 @@ DELETE FROM t2 ORDER BY c LIMIT 1;
 INSERT IGNORE INTO t2 SELECT * FROM t2;
 OPTIMIZE TABLE t2;
 Table	Op	Msg_type	Msg_text
-test.t2	optimize	status	OK
+test.t2	optimize	status	Table is already up to date
 SELECT count(a),sum(a) FROM t2;
 count(a)	sum(a)
 0	NULL
@@ -73,7 +73,6 @@ SELECT count(a),sum(a) FROM t2;
 count(a)	sum(a)
 0	NULL
 ALTER TABLE t2 CHANGE IF EXISTS d c INT;
-ERROR 22007: Truncated incorrect datetime value: '4'
 SELECT count(a),sum(a) FROM t2;
 count(a)	sum(a)
 0	NULL

mysql-test/suite/maria/alter.test

@@ -64,7 +64,6 @@ SELECT count(a),sum(a) FROM t2;
 INSERT IGNORE INTO t2 SELECT * FROM t2;
 SET SQL_MODE= 'STRICT_ALL_TABLES';
 SELECT count(a),sum(a) FROM t2;
---error ER_TRUNCATED_WRONG_VALUE
 ALTER TABLE t2 CHANGE IF EXISTS d c INT;
 SELECT count(a),sum(a) FROM t2;
 ALTER IGNORE TABLE t2 ADD IF NOT EXISTS e BIT;

sql/sql_table.cc

@@ -13073,16 +13073,14 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
     for new fields added to the table (i.e those which should get new default
     values). Now that the data copy is done, the to->default_field list needs
     to be restored to include all fields that have default values to fill.
-
-    First, if to->default_field is NULL, it means it was nullified to prevent
-    trying to update any default values during the copy process because there
-    were no new fields added with default values to fill in. The list needs to
-    be restored to the original location so future records in this session can
-    get default values.
-
-    Then, because to->default_field was reset and now only considers new
-    fields, it is missing fields that have ON UPDATE clauses (i.e. TIMESTAMP
-    and DATETIME). So add those back in.
+    Either:
+      1) to->default_field is NULL, in which case either dfield_ptr is also
+         NULL or the pre-alter table has fields with default values and the
+         alter doesn't add any new fields with default values. In either case,
+         simply restore the original default_field list.
+      2) Otherwise, to->default_field has been modified in-place and needs to
+         be manually restored. I.e., it is missing fields that have ON UPDATE
+         clauses (i.e. TIMESTAMP and DATETIME). So add those back in.
 
     Notes:
      * The code is similar to the dfield_ptr modification earlier in the
@@ -13091,30 +13089,26 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
        data, which requires the table's default_fields to be set up
   */
   if (!to->default_field)
+  {
     to->default_field= dfield_ptr;
-#ifndef DBUG_OFF
+  }
   else
   {
     /*
-      If to->default_field exists, dfield_ptr should point to the NULL list
-      terminator in the default_field list.
+      to->default_list was modified in-place, so we need to check to manually
+      add back missing fields.
     */
-    DBUG_ASSERT(dfield_ptr && !*dfield_ptr);
-  }
-#endif
-  if (dfield_ptr)
-  {
     it.rewind();
     for (Field **ptr= to->field; *ptr; ptr++)
     {
       def= it++;
       if (def->field && def->field->has_update_default_function())
         *(dfield_ptr++)= *ptr;
     }
-    if (dfield_ptr == to->default_field)
-      to->default_field= NULL; // No default fields
-    else
-      *dfield_ptr= NULL; // Mark end of default field pointers
+    /*
+      Mark end of list
+    */
+    *dfield_ptr= NULL;
   }
 
 #ifdef HAVE_REPLICATION