MDEV-18046: Assortment of crashes, assertion failures and ASAN errors in mysql_show_binlog_events

Problem:
========
SHOW BINLOG EVENTS FROM <pos> causes a variety of failures, some of which are
listed below. It is not a race condition issue, but there is some
non-determinism in it.

Analysis:
========
"show binlog events from <pos>" code considers the user given position as a
valid event start position. The code starts reading data from this event start
position onwards and tries to map it to a set of known events. Each event has
a specific event structure and asserts have been added to ensure that read
event data satisfies the event specific requirements. When a random position
is supplied to "show binlog events command" the event structure specific
checks will fail and they result in assert.

Fix:
====
The fix is split into different parts. Each part addresses either an ASAN
issue or an assert/crash.

**Part1: Checksum based position validation when checksum is enabled**


Using checksum validate the very first event read at the user specified
position. If there is a checksum mismatch report an appropriate error for the
invalid event.

mysql-test/suite/binlog/r/binlog_invalid_read_in_rotate.result

+RESET MASTER;
+call mtr.add_suppression("Error in Log_event::read_log_event*");
+call mtr.add_suppression("Replication event checksum verification failed while reading from a log file*");
+DROP TABLE /*! IF EXISTS*/ t1;
+Warnings:
+Note	1051	Unknown table 'test.t1'
+CREATE TABLE `t1` (
+`col_int` int,
+pk integer auto_increment,
+`col_char_12_key` char(12),
+`col_int_key` int,
+`col_char_12` char(12),
+primary key (pk),
+key (`col_char_12_key` ),
+key (`col_int_key` )) ENGINE=InnoDB;
+INSERT /*! IGNORE */ INTO t1 VALUES  (183173120, NULL, 'abcd', 1, 'efghijk'),  (1, NULL, 'lmno', 2, 'p');
+ALTER TABLE `t1` ENABLE KEYS;
+DROP TABLE t1;

mysql-test/suite/binlog/r/binlog_show_binlog_event_random_pos.result

+RESET MASTER;
+call mtr.add_suppression("Error in Log_event::read_log_event*");
+call mtr.add_suppression("Replication event checksum verification failed while reading from a log file*");
+DROP TABLE IF EXISTS t1;
+Warnings:
+Note	1051	Unknown table 'test.t1'
+CREATE TABLE t1 (c1 CHAR(255), c2 CHAR(255), c3 CHAR(255), c4 CHAR(255), c5 CHAR(255));
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+UPDATE t1 SET c1=repeat('b',255);
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+DROP TABLE t1;

mysql-test/suite/binlog/t/binlog_invalid_read_in_rotate.combinations

+[enable_checksum]
+binlog_checksum=1
+
+[disable_checksum]
+binlog_checksum=0

mysql-test/suite/binlog/t/binlog_invalid_read_in_rotate.test

+# ==== Purpose ====
+#
+# Test verifies that reading binary log by using "SHOW BINLOG EVENTS" command
+# from various random positions doesn't lead to crash. It should exit
+# gracefully with appropriate error.
+#
+# ==== References ====
+#
+# MDEV-18046:Assortment of crashes, assertion failures and ASAN errors in mysql_show_binlog_events
+
+--source include/have_log_bin.inc
+--source include/have_innodb.inc
+
+RESET MASTER;
+
+call mtr.add_suppression("Error in Log_event::read_log_event*");
+call mtr.add_suppression("Replication event checksum verification failed while reading from a log file*");
+
+DROP TABLE /*! IF EXISTS*/ t1;
+CREATE TABLE `t1` (
+`col_int` int,
+pk integer auto_increment,
+`col_char_12_key` char(12),
+`col_int_key` int,
+`col_char_12` char(12),
+primary key (pk),
+key (`col_char_12_key` ),
+key (`col_int_key` )) ENGINE=InnoDB;
+
+INSERT /*! IGNORE */ INTO t1 VALUES  (183173120, NULL, 'abcd', 1, 'efghijk'),  (1, NULL, 'lmno', 2, 'p');
+
+--disable_warnings
+ALTER TABLE `t1` ENABLE KEYS;
+--enable_warnings
+
+--let $max_pos= query_get_value(SHOW MASTER STATUS,Position,1)
+--let $pos= 1
+while ($pos <= $max_pos)
+{
+  --disable_query_log
+  --disable_result_log
+  --error 0,1220
+  eval SHOW BINLOG EVENTS FROM $pos;
+  --inc $pos
+  --enable_result_log
+  --enable_query_log
+}
+DROP TABLE t1;

mysql-test/suite/binlog/t/binlog_show_binlog_event_random_pos.combinations

+[enable_checksum]
+binlog_checksum=1
+
+[disable_checksum]
+binlog_checksum=0

mysql-test/suite/binlog/t/binlog_show_binlog_event_random_pos.test

+# ==== Purpose ====
+#
+# Test verifies that reading binary log by using "SHOW BINLOG EVENTS" command
+# from various random positions doesn't lead to crash. It should exit
+# gracefully with appropriate error.
+#
+# ==== References ====
+#
+# MDEV-18046:Assortment of crashes, assertion failures and ASAN errors in mysql_show_binlog_events
+
+--source include/have_log_bin.inc
+--source include/have_innodb.inc
+
+RESET MASTER;
+call mtr.add_suppression("Error in Log_event::read_log_event*");
+call mtr.add_suppression("Replication event checksum verification failed while reading from a log file*");
+
+DROP TABLE IF EXISTS t1;
+CREATE TABLE t1 (c1 CHAR(255), c2 CHAR(255), c3 CHAR(255), c4 CHAR(255), c5 CHAR(255));
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+UPDATE t1 SET c1=repeat('b',255);
+INSERT INTO t1 VALUES (repeat('a', 255), repeat('a', 255),repeat('a', 255),repeat('a', 255),repeat('a', 255));
+--let $max_pos= query_get_value(SHOW MASTER STATUS,Position,1)
+--let $pos= 1
+while ($pos <= $max_pos)
+{
+  --disable_query_log
+  --disable_result_log
+  --error 0,1220
+  eval SHOW BINLOG EVENTS FROM $pos LIMIT 100;
+  --inc $pos
+  --enable_result_log
+  --enable_query_log
+}
+
+DROP TABLE t1;

sql/sql_repl.cc

@@ -3840,6 +3840,11 @@ bool mysql_show_binlog_events(THD* thd)
   List<Item> field_list;
   const char *errmsg = 0;
   bool ret = TRUE;
+  /*
+     Using checksum validate the correctness of event pos specified in show
+     binlog events command.
+  */
+  bool verify_checksum_once= false;
   IO_CACHE log;
   File file = -1;
   MYSQL_BIN_LOG *binary_log= NULL;
@@ -3895,6 +3900,10 @@ bool mysql_show_binlog_events(THD* thd)
       mi= 0;
     }
 
+    /* Validate user given position using checksum */
+    if (lex_mi->pos == pos && !opt_master_verify_checksum)
+      verify_checksum_once= true;
+
     unit->set_limit(thd->lex->current_select);
     limit_start= unit->offset_limit_cnt;
     limit_end= unit->select_limit_cnt;
@@ -3977,15 +3986,16 @@ bool mysql_show_binlog_events(THD* thd)
     for (event_count = 0;
          (ev = Log_event::read_log_event(&log, (mysql_mutex_t*) 0,
                                          description_event,
-                                         opt_master_verify_checksum)); )
+                                         (opt_master_verify_checksum ||
+                                          verify_checksum_once))); )
     {
       if (event_count >= limit_start &&
-	  ev->net_send(protocol, linfo.log_file_name, pos))
+          ev->net_send(protocol, linfo.log_file_name, pos))
       {
-	errmsg = "Net error";
-	delete ev;
+        errmsg = "Net error";
+        delete ev;
         mysql_mutex_unlock(log_lock);
-	goto err;
+        goto err;
       }
 
       if (ev->get_type_code() == FORMAT_DESCRIPTION_EVENT)
@@ -4011,10 +4021,11 @@ bool mysql_show_binlog_events(THD* thd)
         delete ev;
       }
 
+      verify_checksum_once= false;
       pos = my_b_tell(&log);
 
       if (++event_count >= limit_end)
-	break;
+        break;
     }
 
     if (event_count < limit_end && log.error)