Deprecate bootstrap.system_call_filter (#72834)

We are going to require system call filters. This commit is the first
step in that journey, which is to deprecate the setting that allows
disabling system call filters.

docs/reference/migration/migrate_8_0/settings.asciidoc

@@ -224,3 +224,20 @@ value for `node.roles`.
 Discontinue use of the removed settings. Specifying these settings in
 `elasticsearch.yml` will result in an error on startup.
 ====
+
+[[system-call-filter-setting]]
+.System call filter setting deprecated
+[%collapsible]
+====
+*Details* +
+Elasticsearch uses system call filters to remove its ability to fork another
+process. This is useful to mitigate remote code exploits. These system call
+filters are enabled by default, and controlled via the setting
+`bootstrap.system_call_filter`. Starting in Elasticsearch 8.0, system call
+filters will be required. As such, the setting `bootstrap.system_call_filter` is
+deprecated and will be removed in Elasticsearch 8.0.
+
+*Impact* +
+Discontinue use of the removed setting. Specifying this setting in Elasticsearch
+configuration will result in an error on startup.
+====

server/src/main/java/org/elasticsearch/bootstrap/BootstrapSettings.java

@@ -23,7 +23,7 @@ private BootstrapSettings() {
     public static final Setting<Boolean> MEMORY_LOCK_SETTING =
         Setting.boolSetting("bootstrap.memory_lock", false, Property.NodeScope);
     public static final Setting<Boolean> SYSTEM_CALL_FILTER_SETTING =
-        Setting.boolSetting("bootstrap.system_call_filter", true, Property.NodeScope);
+        Setting.boolSetting("bootstrap.system_call_filter", true, Property.Deprecated, Property.NodeScope);
     public static final Setting<Boolean> CTRLHANDLER_SETTING =
         Setting.boolSetting("bootstrap.ctrlhandler", true, Property.NodeScope);
 

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/DeprecationChecks.java

@@ -32,7 +32,8 @@ private DeprecationChecks() {
     static List<Function<ClusterState, DeprecationIssue>> CLUSTER_SETTINGS_CHECKS =
         Collections.emptyList();
 
-    static List<BiFunction<Settings, PluginsAndModules, DeprecationIssue>> NODE_SETTINGS_CHECKS = Collections.emptyList();
+    static List<BiFunction<Settings, PluginsAndModules, DeprecationIssue>> NODE_SETTINGS_CHECKS =
+        List.of(NodeDeprecationChecks::checkBootstrapSystemCallFilterSetting);
 
     static List<Function<IndexMetadata, DeprecationIssue>> INDEX_SETTINGS_CHECKS =
             List.of(IndexDeprecationChecks::oldIndicesCheck, IndexDeprecationChecks::translogRetentionSettingCheck);

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/NodeDeprecationChecks.java

@@ -8,6 +8,7 @@
 package org.elasticsearch.xpack.deprecation;
 
 import org.elasticsearch.action.admin.cluster.node.info.PluginsAndModules;
+import org.elasticsearch.bootstrap.BootstrapSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.xpack.core.deprecation.DeprecationIssue;
@@ -17,6 +18,14 @@
 
 public class NodeDeprecationChecks {
 
+    static DeprecationIssue checkBootstrapSystemCallFilterSetting(final Settings settings, final PluginsAndModules pluginsAndModules) {
+        return checkRemovedSetting(
+            settings,
+            BootstrapSettings.SYSTEM_CALL_FILTER_SETTING,
+            "https://www.elastic.co/guide/en/elasticsearch/reference/7.13/breaking-changes-7.13.html#deprecate-system-call-filter-setting"
+        );
+    }
+
     private static DeprecationIssue checkDeprecatedSetting(
         final Settings settings,
         final PluginsAndModules pluginsAndModules,

x-pack/plugin/deprecation/src/test/java/org/elasticsearch/xpack/deprecation/NodeDeprecationChecksTests.java

@@ -7,17 +7,38 @@
 
 package org.elasticsearch.xpack.deprecation;
 
+import org.elasticsearch.action.admin.cluster.node.info.PluginsAndModules;
+import org.elasticsearch.bootstrap.BootstrapSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.xpack.core.deprecation.DeprecationIssue;
 
+import java.util.List;
+
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.nullValue;
 
 public class NodeDeprecationChecksTests extends ESTestCase {
 
+    public void testCheckBootstrapSystemCallFilterSetting() {
+        final boolean boostrapSystemCallFilter = randomBoolean();
+        final Settings settings =
+            Settings.builder().put(BootstrapSettings.SYSTEM_CALL_FILTER_SETTING.getKey(), boostrapSystemCallFilter).build();
+        final PluginsAndModules pluginsAndModules = new PluginsAndModules(List.of(), List.of());
+        final List<DeprecationIssue> issues =
+            DeprecationChecks.filterChecks(DeprecationChecks.NODE_SETTINGS_CHECKS, c -> c.apply(settings, pluginsAndModules));
+        final DeprecationIssue expected = new DeprecationIssue(
+            DeprecationIssue.Level.CRITICAL,
+            "setting [bootstrap.system_call_filter] is deprecated and will be removed in the next major version",
+            "https://www.elastic.co/guide/en/elasticsearch/reference/7.13/breaking-changes-7.13.html#deprecate-system-call-filter-setting",
+            "the setting [bootstrap.system_call_filter] is currently set to [" + boostrapSystemCallFilter + "], remove this setting");
+        assertThat(issues, hasItem(expected));
+        assertSettingDeprecationsAndWarnings(new Setting<?>[]{BootstrapSettings.SYSTEM_CALL_FILTER_SETTING});
+    }
+
     public void testRemovedSettingNotSet() {
         final Settings settings = Settings.EMPTY;
         final Setting<?> removedSetting = Setting.simpleString("node.removed_setting");