MDEV-7598 Lock user after too many password errorsbb-10.4-wlad-MDEV-7598

17 files changed, 305 insertions, 0 deletions

diff --git a/mysql-test/include/have_auth_named_pipe.inc b/mysql-test/include/have_auth_named_pipe.inc
new file mode 100644
index 00000000000..4f4bf37f11e
--- /dev/null
+++ b/mysql-test/include/have_auth_named_pipe.inc
@@ -0,0 +1,13 @@
+--source include/not_embedded.inc
+
+if (!$AUTH_NAMED_PIPE_SO) {
+  skip No auth_named_pipe plugin;
+}
+
+if (!$USERNAME) {
+  skip USER variable is undefined;
+}
+
+if (`SELECT count(*) <> 0 FROM mysql.user WHERE user = '$USERNAME'`) {
+  skip %USERNAME%=$USER which exists in mysql.user;
+}
diff --git a/mysql-test/main/max_password_errors.result b/mysql-test/main/max_password_errors.result
new file mode 100644
index 00000000000..020761b4f2e
--- /dev/null
+++ b/mysql-test/main/max_password_errors.result
@@ -0,0 +1,45 @@
+set @old_max_password_errors=@@max_password_errors;
+set global max_password_errors=2;
+create user u identified by 'good_pass';
+connect(localhost,u,bas_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect con1, localhost, u, bas_pass;
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+connect(localhost,u,bad_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, u, bad_pass;
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+connect(localhost,u,good_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect con1, localhost, u, good_pass;
+ERROR HY000: User is blocked because of too many credential errors; unblock with 'FLUSH PRIVILEGES'
+connect(localhost,u,bad_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect con1, localhost, u, bad_pass;
+ERROR HY000: User is blocked because of too many credential errors; unblock with 'FLUSH PRIVILEGES'
+FLUSH PRIVILEGES;
+connect  con1, localhost, u, good_pass;
+disconnect con1;
+connect(localhost,u,bad_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, u, bad_pass;
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+connect  con1, localhost, u, good_pass;
+disconnect con1;
+connect(localhost,u,bad_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, u, bad_pass;
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+connect  con1, localhost, u, good_pass;
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+ERROR 28000: Access denied for user 'u'@'localhost' (using password: YES)
+ERROR HY000: User is blocked because of too many credential errors; unblock with 'FLUSH PRIVILEGES'
+disconnect con1;
+connection default;
+FLUSH PRIVILEGES;
+connect(localhost,root,bas_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect con1, localhost, root, bas_pass;
+ERROR 28000: Access denied for user 'root'@'localhost' (using password: YES)
+connect(localhost,root,bad_pass,test,MASTER_PORT,MASTER_SOCKET);
+connect  con1, localhost, root, bad_pass;
+ERROR 28000: Access denied for user 'root'@'localhost' (using password: YES)
+connect  con1, localhost, u, good_pass;
+disconnect con1;
+connection default;
+DROP USER u;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
diff --git a/mysql-test/main/max_password_errors.test b/mysql-test/main/max_password_errors.test
new file mode 100644
index 00000000000..1debca0258d
--- /dev/null
+++ b/mysql-test/main/max_password_errors.test
@@ -0,0 +1,64 @@
+--source include/not_embedded.inc
+set @old_max_password_errors=@@max_password_errors;
+set global max_password_errors=2;
+create user u identified by 'good_pass';
+
+# Test that user is blocked after 'max_password_errors' bad passwords
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect(con1, localhost, u, bas_pass);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect (con1, localhost, u, bad_pass);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_USER_IS_BLOCKED;
+connect(con1, localhost, u, good_pass);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_USER_IS_BLOCKED;
+connect(con1, localhost, u, bad_pass);
+
+
+# Test that FLUSH PRIVILEGES clears the error
+FLUSH PRIVILEGES;
+connect (con1, localhost, u, good_pass);
+disconnect con1;
+
+# Test that good login clears the error
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect (con1, localhost, u, bad_pass);
+connect (con1, localhost, u, good_pass);
+disconnect con1;
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect (con1, localhost, u, bad_pass);
+connect (con1, localhost, u, good_pass);
+
+# Test the behavior of change_user
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+change_user u,bad_pass;
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+change_user u,bad_pass;
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_USER_IS_BLOCKED;
+change_user u,good_pass;
+disconnect con1;
+
+connection default;
+FLUSH PRIVILEGES;
+
+#Test that root@localhost is not blocked, with password errors
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect(con1, localhost, root, bas_pass);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_ERROR;
+connect (con1, localhost, root, bad_pass);
+connect (con1, localhost, u, good_pass);
+disconnect con1;
+connection default;
+DROP USER u;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
\ No newline at end of file
diff --git a/mysql-test/main/mysqld--help.result b/mysql-test/main/mysqld--help.result
index 8faf332a7dd..b8a99393b28 100644
--- a/mysql-test/main/mysqld--help.result
+++ b/mysql-test/main/mysqld--help.result
@@ -546,6 +546,10 @@ The following specify which files/extra groups are read (specified before remain
  The maximum BLOB length to send to server from
  mysql_send_long_data API. Deprecated option; use
  max_allowed_packet instead.
+ --max-password-errors=# 
+ If there is more than this number of failed connect
+ attempts due to invalid password, user will be blocked
+ from further connections until FLUSH_PRIVILEGES.
  --max-prepared-stmt-count=# 
  Maximum number of prepared statements in the server
  --max-recursive-iterations[=#] 
@@ -1518,6 +1522,7 @@ max-heap-table-size 16777216
 max-join-size 18446744073709551615
 max-length-for-sort-data 1024
 max-long-data-size 16777216
+max-password-errors 18446744073709551615
 max-prepared-stmt-count 16382
 max-recursive-iterations 18446744073709551615
 max-relay-log-size 1073741824
diff --git a/mysql-test/suite/plugins/r/max_password_errors_auth_named_pipe.result b/mysql-test/suite/plugins/r/max_password_errors_auth_named_pipe.result
new file mode 100644
index 00000000000..82d464e3cb2
--- /dev/null
+++ b/mysql-test/suite/plugins/r/max_password_errors_auth_named_pipe.result
@@ -0,0 +1,12 @@
+set @old_max_password_errors=@@max_password_errors;
+create user nosuchuser identified with 'named_pipe';
+set global max_password_errors=1;
+connect(localhost,nosuchuser,,test,MASTER_PORT,MASTER_SOCKET);
+connect pipe_con,localhost,nosuchuser,,,,,PIPE;
+ERROR 28000: Access denied for user 'nosuchuser'@'localhost'
+connect(localhost,nosuchuser,,test,MASTER_PORT,MASTER_SOCKET);
+connect pipe_con,localhost,nosuchuser,,,,,PIPE;
+ERROR 28000: Access denied for user 'nosuchuser'@'localhost'
+DROP USER nosuchuser;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
diff --git a/mysql-test/suite/plugins/r/max_password_errors_auth_socket.result b/mysql-test/suite/plugins/r/max_password_errors_auth_socket.result
new file mode 100644
index 00000000000..eb7cb64167b
--- /dev/null
+++ b/mysql-test/suite/plugins/r/max_password_errors_auth_socket.result
@@ -0,0 +1,12 @@
+set @old_max_password_errors=@@max_password_errors;
+create user nosuchuser identified with 'unix_socket';
+set global max_password_errors=1;
+connect(localhost,nosuchuser,,test,MASTER_PORT,MASTER_SOCKET);
+connect pipe_con,localhost,nosuchuser;
+ERROR 28000: Access denied for user 'nosuchuser'@'localhost'
+connect(localhost,nosuchuser,,test,MASTER_PORT,MASTER_SOCKET);
+connect pipe_con,localhost,nosuchuser;
+ERROR 28000: Access denied for user 'nosuchuser'@'localhost'
+DROP USER nosuchuser;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
diff --git a/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.opt b/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.opt
new file mode 100644
index 00000000000..52bf94f3511
--- /dev/null
+++ b/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.opt
@@ -0,0 +1 @@
+--loose-enable-named-pipe --plugin-load=$AUTH_NAMED_PIPE_SO
diff --git a/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.test b/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.test
new file mode 100644
index 00000000000..79aeb7d3cbe
--- /dev/null
+++ b/mysql-test/suite/plugins/t/max_password_errors_auth_named_pipe.test
@@ -0,0 +1,22 @@
+# Tests that max_password_errors has no effect on login errors with
+# passwordless plugins (Windows version / auth_named_pipe)
+
+--source include/not_embedded.inc
+--source include/have_auth_named_pipe.inc
+if (`SELECT '$USERNAME' = 'nosuchuser'`) {
+  skip skipped for nosuchuser;
+}
+set @old_max_password_errors=@@max_password_errors;
+create user nosuchuser identified with 'named_pipe';
+
+set global max_password_errors=1;
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_NO_PASSWORD_ERROR;
+connect(pipe_con,localhost,nosuchuser,,,,,PIPE);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_NO_PASSWORD_ERROR;
+connect(pipe_con,localhost,nosuchuser,,,,,PIPE);
+
+DROP USER nosuchuser;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
diff --git a/mysql-test/suite/plugins/t/max_password_errors_auth_socket.opt b/mysql-test/suite/plugins/t/max_password_errors_auth_socket.opt
new file mode 100644
index 00000000000..91bb73e34f7
--- /dev/null
+++ b/mysql-test/suite/plugins/t/max_password_errors_auth_socket.opt
@@ -0,0 +1 @@
+--loose-enable-named-pipe --plugin-load=$AUTH_SOCKET_SO
diff --git a/mysql-test/suite/plugins/t/max_password_errors_auth_socket.test b/mysql-test/suite/plugins/t/max_password_errors_auth_socket.test
new file mode 100644
index 00000000000..495a68a0b59
--- /dev/null
+++ b/mysql-test/suite/plugins/t/max_password_errors_auth_socket.test
@@ -0,0 +1,23 @@
+# Tests that max_password_errors has no effect on login errors with
+# passwordless plugins (Unix version / auth_unix_socket)
+
+--source include/not_embedded.inc
+--source include/have_unix_socket.inc
+
+if (`SELECT '$USER' = 'nosuchuser'`) {
+  skip USER is nosuchuser;
+}
+set @old_max_password_errors=@@max_password_errors;
+create user nosuchuser identified with 'unix_socket';
+
+set global max_password_errors=1;
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_NO_PASSWORD_ERROR;
+connect(pipe_con,localhost,nosuchuser);
+--replace_result $MASTER_MYSOCK MASTER_SOCKET $MASTER_MYPORT MASTER_PORT
+error ER_ACCESS_DENIED_NO_PASSWORD_ERROR;
+connect(pipe_con,localhost,nosuchuser);
+
+DROP USER nosuchuser;
+FLUSH PRIVILEGES;
+set global max_password_errors=@old_max_password_errors;
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
index 1dac71788bd..64dbbf6a75a 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
@@ -2210,6 +2210,20 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	MAX_PASSWORD_ERRORS
+SESSION_VALUE	NULL
+GLOBAL_VALUE	4294967295
+GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+DEFAULT_VALUE	4294967295
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	INT UNSIGNED
+VARIABLE_COMMENT	If there is more than this number of failed connect attempts due to invalid password, user will be blocked from further connections until FLUSH_PRIVILEGES.
+NUMERIC_MIN_VALUE	1
+NUMERIC_MAX_VALUE	4294967295
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	MAX_PREPARED_STMT_COUNT
 SESSION_VALUE	NULL
 GLOBAL_VALUE	16382
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
index 4c9b38c48b7..d99c2fae240 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
@@ -2420,6 +2420,20 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	MAX_PASSWORD_ERRORS
+SESSION_VALUE	NULL
+GLOBAL_VALUE	4294967295
+GLOBAL_VALUE_ORIGIN	COMPILE-TIME
+DEFAULT_VALUE	4294967295
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	INT UNSIGNED
+VARIABLE_COMMENT	If there is more than this number of failed connect attempts due to invalid password, user will be blocked from further connections until FLUSH_PRIVILEGES.
+NUMERIC_MIN_VALUE	1
+NUMERIC_MAX_VALUE	4294967295
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	MAX_PREPARED_STMT_COUNT
 SESSION_VALUE	NULL
 GLOBAL_VALUE	16382
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 561b55a9023..da0be1c7945 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -513,6 +513,7 @@ ulong specialflag=0;
 ulong binlog_cache_use= 0, binlog_cache_disk_use= 0;
 ulong binlog_stmt_cache_use= 0, binlog_stmt_cache_disk_use= 0;
 ulong max_connections, max_connect_errors;
+uint max_password_errors;
 ulong extra_max_connections;
 uint max_digest_length= 0;
 ulong slave_retried_transactions;
diff --git a/sql/mysqld.h b/sql/mysqld.h
index 22c572b19fa..49663f27a66 100644
--- a/sql/mysqld.h
+++ b/sql/mysqld.h
@@ -241,6 +241,7 @@ extern ulong slow_launch_threads, slow_launch_time;
 extern MYSQL_PLUGIN_IMPORT ulong max_connections;
 extern uint max_digest_length;
 extern ulong max_connect_errors, connect_timeout;
+extern uint max_password_errors;
 extern my_bool slave_allow_batching;
 extern my_bool allow_slave_start;
 extern LEX_CSTRING reason_slave_blocked;
diff --git a/sql/share/errmsg-utf8.txt b/sql/share/errmsg-utf8.txt
index daf010d8e8a..e09afebe074 100644
--- a/sql/share/errmsg-utf8.txt
+++ b/sql/share/errmsg-utf8.txt
@@ -7931,3 +7931,5 @@ ER_BACKUP_STAGE_FAILED
         eng "Backup stage '%s' failed"
 ER_BACKUP_UNKNOWN_STAGE
         eng "Unknown backup stage: '%s'. Stage should be one of START, FLUSH, BLOCK_DDL, BLOCK_COMMIT or END"
+ER_USER_IS_BLOCKED
+        eng "User is blocked because of too many credential errors; unblock with 'FLUSH PRIVILEGES'"
diff --git a/sql/sql_acl.cc b/sql/sql_acl.cc
index 3c31be5bd36..c5229d02d51 100644
--- a/sql/sql_acl.cc
+++ b/sql/sql_acl.cc
@@ -147,6 +147,7 @@ public:
   size_t hostname_length;
   USER_RESOURCES user_resource;
   enum SSL_type ssl_type;
+  uint password_errors;
   const char *ssl_cipher, *x509_issuer, *x509_subject;
   LEX_CSTRING plugin;
   LEX_CSTRING auth_string;
@@ -12325,6 +12326,23 @@ static bool send_plugin_request_packet(MPVIO_EXT *mpvio,
 }
 
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
+
+/**
+  Safeguard to avoid blocking the root, when max_password_errors
+  limit is reached.
+
+  Currently, we allow password errors for superuser on localhost.
+
+  @return true, if password errors should be ignored, and user should not be locked.
+*/
+static bool ignore_max_password_errors(const ACL_USER *acl_user)
+{
+ const char *host= acl_user->host.hostname;
+ return (acl_user->access & SUPER_ACL)
+   && (!strcasecmp(host, "localhost") ||
+       !strcmp(host, "127.0.0.1") ||
+       !strcmp(host, "::1"));
+}
 /**
    Finds acl entry in user database for authentication purposes.
 
@@ -12343,6 +12361,16 @@ static bool find_mpvio_user(MPVIO_EXT *mpvio)
   mysql_mutex_lock(&acl_cache->lock);
 
   ACL_USER *user= find_user_or_anon(sctx->host, sctx->user, sctx->ip);
+
+  if (user && user->password_errors >= max_password_errors && !ignore_max_password_errors(user))
+  {
+    mysql_mutex_unlock(&acl_cache->lock);
+    my_error(ER_USER_IS_BLOCKED, MYF(0));
+    general_log_print(mpvio->auth_info.thd, COM_CONNECT,
+      ER_THD(mpvio->auth_info.thd, ER_USER_IS_BLOCKED));
+    DBUG_RETURN(1);
+  }
+
   if (user)
     mpvio->acl_user= user->copy(mpvio->auth_info.thd->mem_root);
 
@@ -13188,6 +13216,38 @@ static int do_auth_once(THD *thd, const LEX_CSTRING *auth_plugin_name,
   return res;
 }
 
+enum PASSWD_ERROR_ACTION
+{
+  PASSWD_ERROR_CLEAR,
+  PASSWD_ERROR_INCREMENT
+};
+
+/* Increment, or clear password errors for a user. */
+static void handle_password_errors(const char *user, const char *hostname, PASSWD_ERROR_ACTION action)
+{
+#ifndef NO_EMBEDDED_ACCESS_CHECKS
+  mysql_mutex_assert_not_owner(&acl_cache->lock);
+  mysql_mutex_lock(&acl_cache->lock);
+  ACL_USER *u = find_user_exact(hostname, user);
+  if (u)
+  {
+    switch(action)
+    {
+      case PASSWD_ERROR_INCREMENT:
+        u->password_errors++;
+        break;
+      case PASSWD_ERROR_CLEAR:
+        u->password_errors= 0;
+        break;
+      default:
+        DBUG_ASSERT(0);
+        break;
+    }
+  }
+  mysql_mutex_unlock(&acl_cache->lock);
+#endif
+}
+
 
 /**
   Perform the handshake, authorize the client and update thd sctx variables.
@@ -13307,6 +13367,8 @@ bool acl_authenticate(THD *thd, uint com_change_user_pkt_len)
       break;
     case CR_AUTH_USER_CREDENTIALS:
       errors.m_authentication= 1;
+      if (thd->password && !mpvio.make_it_fail)
+        handle_password_errors(acl_user->user.str, acl_user->host.hostname, PASSWD_ERROR_INCREMENT);
       break;
     case CR_ERROR:
     default:
@@ -13321,6 +13383,11 @@ bool acl_authenticate(THD *thd, uint com_change_user_pkt_len)
   }
 
   sctx->proxy_user[0]= 0;
+  if (thd->password && acl_user->password_errors)
+  {
+    /* Login succeeded, clear password errors.*/
+    handle_password_errors(acl_user->user.str, acl_user->host.hostname, PASSWD_ERROR_CLEAR);
+  }
 
   if (initialized) // if not --skip-grant-tables
   {
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index e8044ef9035..0bf297b8eef 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -1515,6 +1515,14 @@ static Sys_var_ulong Sys_max_connect_errors(
        VALID_RANGE(1, UINT_MAX), DEFAULT(MAX_CONNECT_ERRORS),
        BLOCK_SIZE(1));
 
+static Sys_var_uint Sys_max_password_errors(
+       "max_password_errors",
+       "If there is more than this number of failed connect attempts "
+       "due to invalid password, user will be blocked from further connections until FLUSH_PRIVILEGES.",
+       GLOBAL_VAR(max_password_errors), CMD_LINE(REQUIRED_ARG),
+       VALID_RANGE(1, UINT_MAX), DEFAULT(UINT_MAX),
+       BLOCK_SIZE(1));
+
 static Sys_var_uint Sys_max_digest_length(
        "max_digest_length", "Maximum length considered for digest text.",
        READ_ONLY GLOBAL_VAR(max_digest_length),