Do not configure a logger named level

When logger.level is set, we end up configuring a logger named "level"
because we look for all settings of the form "logger\..+" as configuring
a logger. Yet, logger.level is special and is meant to only configure
the default logging level. This commit causes is to avoid not
configuring a logger named level.

Relates #22624

core/src/main/java/org/elasticsearch/common/logging/LogConfigurator.java

@@ -122,19 +122,26 @@ public class LogConfigurator {
         Configurator.initialize(builder.build());
     }
 
-    private static void configureLoggerLevels(Settings settings) {
+    /**
+     * Configures the logging levels for loggers configured in the specified settings.
+     *
+     * @param settings the settings from which logger levels will be extracted
+     */
+    private static void configureLoggerLevels(final Settings settings) {
         if (ESLoggerFactory.LOG_DEFAULT_LEVEL_SETTING.exists(settings)) {
             final Level level = ESLoggerFactory.LOG_DEFAULT_LEVEL_SETTING.get(settings);
             Loggers.setLevel(ESLoggerFactory.getRootLogger(), level);
         }
 
         final Map<String, String> levels = settings.filter(ESLoggerFactory.LOG_LEVEL_SETTING::match).getAsMap();
-        for (String key : levels.keySet()) {
+        for (final String key : levels.keySet()) {
+            // do not set a log level for a logger named level (from the default log setting)
+            if (!key.equals(ESLoggerFactory.LOG_DEFAULT_LEVEL_SETTING.getKey())) {
                 final Level level = ESLoggerFactory.LOG_LEVEL_SETTING.getConcreteSetting(key).get(settings);
                 Loggers.setLevel(ESLoggerFactory.getLogger(key.substring("logger.".length())), level);
             }
         }
-
+    }
 
     @SuppressForbidden(reason = "sets system property for logging configuration")
     private static void setLogConfigurationSystemProperty(final Path logsPath, final Settings settings) {

qa/evil-tests/src/test/java/org/elasticsearch/common/logging/EvilLoggerConfigurationTests.java

@@ -34,9 +34,11 @@ import org.elasticsearch.test.ESTestCase;
 
 import java.io.IOException;
 import java.nio.file.Path;
+import java.util.Map;
 
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.notNullValue;
 
@@ -151,4 +153,33 @@ public class EvilLoggerConfigurationTests extends ESTestCase {
         assertThat(e, hasToString(containsString("no log4j2.properties found; tried")));
     }
 
+    public void testLoggingLevelsFromSettings() throws IOException, UserException {
+        final Level rootLevel = randomFrom(Level.TRACE, Level.DEBUG, Level.INFO, Level.WARN, Level.ERROR);
+        final Level fooLevel = randomFrom(Level.TRACE, Level.DEBUG, Level.INFO, Level.WARN, Level.ERROR);
+        final Level barLevel = randomFrom(Level.TRACE, Level.DEBUG, Level.INFO, Level.WARN, Level.ERROR);
+        final Path configDir = getDataPath("minimal");
+        final Settings settings = Settings.builder()
+            .put(Environment.PATH_CONF_SETTING.getKey(), configDir.toAbsolutePath())
+            .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString())
+            .put("logger.level", rootLevel.name())
+            .put("logger.foo", fooLevel.name())
+            .put("logger.bar", barLevel.name())
+            .build();
+        final Environment environment = new Environment(settings);
+        LogConfigurator.configure(environment);
+
+        final LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
+        final Configuration config = ctx.getConfiguration();
+        final Map<String, LoggerConfig> loggerConfigs = config.getLoggers();
+        assertThat(loggerConfigs.size(), equalTo(3));
+        assertThat(loggerConfigs, hasKey(""));
+        assertThat(loggerConfigs.get("").getLevel(), equalTo(rootLevel));
+        assertThat(loggerConfigs, hasKey("foo"));
+        assertThat(loggerConfigs.get("foo").getLevel(), equalTo(fooLevel));
+        assertThat(loggerConfigs, hasKey("bar"));
+        assertThat(loggerConfigs.get("bar").getLevel(), equalTo(barLevel));
+
+        assertThat(ctx.getLogger(randomAsciiOfLength(16)).getLevel(), equalTo(rootLevel));
+    }
+
 }

qa/evil-tests/src/test/resources/org/elasticsearch/common/logging/minimal/log4j2.properties

@@ -0,0 +1,7 @@
+appender.console.type = Console
+appender.console.name = console
+appender.console.layout.type = PatternLayout
+appender.console.layout.pattern = %m%n
+
+rootLogger.level = info
+rootLogger.appenderRef.console.ref = console