MDEV-25343 add read secret size in file key plugin

mysql-test/suite/encryption/r/filekeys_secret_too_long.result

+call mtr.add_suppression("the secret file has incorrect length");
+call mtr.add_suppression("Plugin 'file_key_management' init function returned error");
+call mtr.add_suppression("Plugin 'file_key_management' registration.*failed");
+FOUND 1 /the secret file has incorrect length/ in mysqld.1.err
+create table t1(c1 bigint not null, b char(200))  engine=innodb encrypted=yes encryption_key_id=1;
+ERROR HY000: Can't create table `test`.`t1` (errno: 140 "Wrong create options")
+select plugin_status from information_schema.plugins
+where plugin_name = 'file_key_management';
+plugin_status
+# Test checks if opening an too large secret does not crash the server.

mysql-test/suite/encryption/t/filekeys-data-too-long.key

+secretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecret
+secretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecret
+secretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecretsecret
+

mysql-test/suite/encryption/t/filekeys_secret_too_long.opt

+--loose-file-key-management-filekey=FILE:$MTR_SUITE_DIR/t/filekeys-data-too-long.key
+--loose-file-key-management-filename=$MTR_SUITE_DIR/t/filekeys-data.enc
+

mysql-test/suite/encryption/t/filekeys_secret_too_long.test

+let SEARCH_PATTERN=the secret file has incorrect length;
+source filekeys_badtest.inc;
+
+--echo # Test checks if opening an too large secret does not crash the server.

plugin/file_key_management/parser.cc

@@ -174,13 +174,24 @@ bool Parser::read_filekey(const char *filekey, char *secret)
     return 1;
   }
 
-  int len= read(f, secret, MAX_SECRET_SIZE);
+  int len= read(f, secret, MAX_SECRET_SIZE + 1);
   if (len <= 0)
   {
     my_error(EE_READ,ME_ERROR_LOG, filekey, errno);
     close(f);
     return 1;
   }
+
+  if (len > MAX_SECRET_SIZE)
+  {
+    my_printf_error(EE_READ,
+                    "Cannot decrypt %s, the secret file has incorrect length, "
+                    "max secret size is %dB ",
+                    ME_ERROR_LOG, filekey, MAX_SECRET_SIZE);
+    close(f);
+    return 1;
+  }
+
   close(f);
   while (secret[len - 1] == '\r' || secret[len - 1] == '\n') len--;
   secret[len]= '\0';