MDEV-27744 InnoDB: Failing assertion: !cursor->index->is_committed() in row0ins.cc (from row_ins_sec_index_entry_by_modify) | Assertion `0' failed in row_upd_sec_index_entry (debug) | Corruptionbb-10.4-bar-MDEV-27744

The crash happened with an indexed virtual column whose
value is evaluated using a function that has a different meaning
in sql_mode='' vs sql_mode=ORACLE:

- DECODE()
- LTRIM()
- RTRIM()
- LPAD()
- RPAD()
- REPLACE()
- SUBSTR()

For example:

CREATE TABLE t1 (
  b VARCHAR(1),
  g CHAR(1) GENERATED ALWAYS AS (SUBSTR(b,0,0)) VIRTUAL,
  KEY g(g)
);

So far we had replacement XXX_ORACLE() functions for all mentioned function,
e.g. SUBSTR_ORACLE() for SUBSTR(). So it was possible to correctly re-parse
SUBSTR_ORACLE() even in sql_mode=''.

But it was not possible to re-parse the MariaDB version of SUBSTR()
after switching to sql_mode=ORACLE. It was erroneously mis-interpreted
as SUBSTR_ORACLE().

As a result, this combination worked fine:

SET sql_mode=ORACLE;
CREATE TABLE t1 ... g CHAR(1) GENERATED ALWAYS AS (SUBSTR(b,0,0)) VIRTUAL, ...;
INSERT ...
FLUSH TABLES;
SET sql_mode='';
INSERT ...

But the other way around it crashed:

SET sql_mode='';
CREATE TABLE t1 ... g CHAR(1) GENERATED ALWAYS AS (SUBSTR(b,0,0)) VIRTUAL, ...;
INSERT ...
FLUSH TABLES;
SET sql_mode=ORACLE;
INSERT ...

At CREATE time, SUBSTR was instantiated as Item_func_substr and printed
in the FRM file as substr(). At re-open time with sql_mode=ORACLE, "substr()"
was erroneously instantiated as Item_func_substr_oracle.

Fix:

The fix proposes a symmetric solution. It provides a way to re-parse reliably
all sql_mode dependent functions to their original CREATE TABLE time meaning,
no matter what the open-time sql_mode is.

We take advantage of the same idea we previously used to resolve sql_mode
dependent data types.

Now all sql_mode dependent functions are printed by SHOW using a schema
qualifier when the current sql_mode differs from the function sql_mode:

SET sql_mode='';
CREATE TABLE t1 ... SUBSTR(a,b,c) ..;
SET sql_mode=ORACLE;
SHOW CREATE TABLE t1;   ->   mariadb_schema.substr(a,b,c)

SET sql_mode=ORACLE;
CREATE TABLE t2 ... SUBSTR(a,b,c) ..;
SET sql_mode='';
SHOW CREATE TABLE t1;   ->   oracle_schema.substr(a,b,c)

Old replacement names like substr_oracle() are still understood for
backward compatibility and used in FRM files (for downgrade compatibility),
but they are not printed by SHOW any more.

1 files changed, 44 insertions, 0 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index d0c3e0244e7..78835f7e02e 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -6862,6 +6862,50 @@ class Sql_mode_save
   sql_mode_t old_mode; // SQL mode saved at construction time.
 };
 
+
+/*
+  Save the current sql_mode. Switch off sql_mode flags which can prevent
+  normal parsing of VIEWs, expressions in generated columns.
+  Restore the old sql_mode on destructor.
+*/
+class Sql_mode_save_for_frm_handling: public Sql_mode_save
+{
+public:
+  Sql_mode_save_for_frm_handling(THD *thd)
+   :Sql_mode_save(thd)
+  {
+    /*
+      - MODE_REAL_AS_FLOAT            affect only CREATE TABLE parsing
+      + MODE_PIPES_AS_CONCAT          affect expression parsing
+      + MODE_ANSI_QUOTES              affect expression parsing
+      + MODE_IGNORE_SPACE             affect expression parsing
+      - MODE_IGNORE_BAD_TABLE_OPTIONS affect only CREATE/ALTER TABLE parsing
+      * MODE_ONLY_FULL_GROUP_BY       affect execution
+      * MODE_NO_UNSIGNED_SUBTRACTION  affect execution
+      - MODE_NO_DIR_IN_CREATE         affect table creation only
+      - MODE_POSTGRESQL               compounded from other modes
+      - MODE_ORACLE                   affects Item creation (e.g for CONCAT)
+      - MODE_MSSQL                    compounded from other modes
+      - MODE_DB2                      compounded from other modes
+      - MODE_MAXDB                    affect only CREATE TABLE parsing
+      - MODE_NO_KEY_OPTIONS           affect only SHOW
+      - MODE_NO_TABLE_OPTIONS         affect only SHOW
+      - MODE_NO_FIELD_OPTIONS         affect only SHOW
+      - MODE_MYSQL323                 affect only SHOW
+      - MODE_MYSQL40                  affect only SHOW
+      - MODE_ANSI                     compounded from other modes
+                                      (+ transaction mode)
+      ? MODE_NO_AUTO_VALUE_ON_ZERO    affect UPDATEs
+      + MODE_NO_BACKSLASH_ESCAPES     affect expression parsing
+      + MODE_EMPTY_STRING_IS_NULL     affect expression parsing
+    */
+    thd->variables.sql_mode&= ~(MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
+                                MODE_IGNORE_SPACE | MODE_NO_BACKSLASH_ESCAPES |
+                                MODE_ORACLE | MODE_EMPTY_STRING_IS_NULL);
+  };
+};
+
+
 class Abort_on_warning_instant_set
 {
   THD *m_thd;