MDEV-23666: Assertion `m_cpp_buf <= ptr && ptr <= m_cpp_buf + m_buf_length'...

MDEV-23666: Assertion `m_cpp_buf <= ptr && ptr <= m_cpp_buf + m_buf_length' failed in Lex_input_stream::body_utf8_append

On parsing statements for which a starting backtick (`) delimiter doesn't have
a corresponding ending backtick, a current pointer to a position inside a
pre-processed buffer could go beyond the end of the buffer.

This bug report caused by the commit d4967659
  "MDEV-22022 Various mangled SQL statements will crash 10.3 to 10.5 debug builds".

In order to fix the issue both pointers m_ptr and m_cpp_ptr must be
rolled back to previous position in raw input and pre-processed input streams
correspondingly in case end of query reached during parsing.

mysql-test/main/parser.result

@@ -1784,4 +1784,13 @@ EXECUTE IMMEDIATE 'if(`systeminfo /FO LIST';
 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 '`systeminfo /FO LIST' at line 1
 EXECUTE IMMEDIATE 'if(`systeminfo';
 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 '`systeminfo' at line 1
+#
+# MDEV-23666 Assertion failed in Lex_input_stream::body_utf8_append
+#
+SET @@sql_mode='ANSI_QUOTES';
+EXECUTE IMMEDIATE 'CREATE PROCEDURE p() UPDATE t SET c=\'\'"';
+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 '"' at line 1
+EXECUTE IMMEDIATE 'CREATE PROCEDURE p() UPDATE t SET c=\'\'"abc';
+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 '"abc' at line 1
+SET @@sql_mode=@save_sql_mode;
 # End of 10.3 tests

mysql-test/main/parser.test

@@ -1561,4 +1561,19 @@ EXECUTE IMMEDIATE 'if(`systeminfo /FO LIST';
 --error ER_PARSE_ERROR
 EXECUTE IMMEDIATE 'if(`systeminfo';
 
+--echo #
+--echo # MDEV-23666 Assertion failed in Lex_input_stream::body_utf8_append
+--echo #
+SET @@sql_mode='ANSI_QUOTES';
+
+# Without a patch execution of the following statements results in assertion
+# in Lex_input_stream::body_utf8_append on parsing the statement
+--error ER_PARSE_ERROR
+EXECUTE IMMEDIATE 'CREATE PROCEDURE p() UPDATE t SET c=\'\'"';
+
+--error ER_PARSE_ERROR
+EXECUTE IMMEDIATE 'CREATE PROCEDURE p() UPDATE t SET c=\'\'"abc';
+
+SET @@sql_mode=@save_sql_mode;
+
 --echo # End of 10.3 tests

sql/sql_lex.cc

@@ -2215,6 +2215,8 @@ int Lex_input_stream::scan_ident_delimited(THD *thd,
         Return the quote character, to have the parser fail on syntax error.
       */
       m_ptr= (char *) m_tok_start + 1;
+      if (m_echo)
+        m_cpp_ptr= (char *) m_cpp_tok_start + 1;
       return quote_char;
     }
     int var_length= my_charlen(cs, get_ptr() - 1, get_end_of_query());