[Security Solutions][Detection Engine] Adds ability to ignore fields …

…during alert indexing and a workaround for an EQL bug (elastic#110927)

## Summary

Adds a workaround for EQL bug: elastic/elasticsearch#77152
Adds the safety feature mentioned here: elastic#110802

Adds the ability to ignore particular [fields](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#search-fields-param) when the field is merged with [_source](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#source-filtering). Also fixes an EQL bug where EQL is introducing the meta field of `_ignored` within the fields and causing documents to not be indexable when we merge with the fields from EQL.

Alerting document creation uses the fields API to get [runtime field](https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime.html),  [constant keyword](https://www.elastic.co/guide/en/elasticsearch/reference/master/keyword.html#constant-keyword-field-type), etc... that are only available within the [fields API](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#search-fields-param) and then merges the field values not found within the `_source` document with the `_source` document and then finally indexes this merged document as an alert document.

This fix/ability is a "safety feature" in that if a problematic [runtime field](https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime.html), [constant keyword](https://www.elastic.co/guide/en/elasticsearch/reference/master/keyword.html#constant-keyword-field-type) is discovered or another bug along the stack we can set a `kibana.yml` key/value pair to ignore the problematic field.

This _WILL NOT_ remove problematic fields from the `_source` document. This will only ignore problematic constant keyword, runtime fields, aliases, or anything else found in the fields API that is causing merge issues.

This PR:
  * Adds a `alertIgnoreFields` `kibana.yml` array key with a default of an empty array if not specified.
  * Plumbs the `alertIgnoreFields` through the stack and into the fields/_source merge strategies of `missingFields` and `allFields`
  * Adds a temporary `isEqlBug77152` where it hard codes an ignore of `_ignored` until the EQL problem is fixed and then we will remove the workaround
  * Adds unit tests
  * Adds e2e tests which covers the described use cases above.

The `alertIgnoreFields` key/value within `kibana.yml` if set should be an array of strings of each field you want to ignore. This can also contain regular expressions as long as they are of the form, `"/regex/"` in the array.

Example if you want to ignore fields that are problematic called "host.name" and then one in which you want to ignore all fields that start with "user." using a regular expression:

```yml
xpack.securitySolution.alertIgnoreFields: ['host.name', '/user\..*/']
```

Although there are e2e tests which exercise the use cases...

If you want to manual test the EQL bug fix you would add these documents in dev tools:

```json
# Delete and add a mapping with a small ignore_above.
DELETE eql-issue-ignore-fields-delme
PUT eql-issue-ignore-fields-delme
{
  "mappings" : {
    "dynamic": "strict",
    "properties" : {
      "@timestamp": {
        "type": "date"
      },
      "some_keyword" : {
        "ignore_above": 5,
        "type" : "keyword"
      },
      "other_keyword" : {
        "ignore_above": 10,
        "type" : "keyword"
      }
    }
  }
}

# Add a single document with one field that will be truncated and a second that will not.
PUT eql-issue-ignore-fields-delme/_doc/1
{
  "@timestamp": "2021-09-02T04:13:05.626Z",
  "some_keyword": "longer than normal",
  "other_keyword": "normal"
}
```

Then create an alert which queries everything from it:
<img width="1155" alt="Screen Shot 2021-09-01 at 10 15 06 PM" src="https://user-images.githubusercontent.com/1151048/131781042-faa424cf-65a5-4ebb-b801-3f188940c81d.png">

and ensure signals are created:
<img width="2214" alt="Screen Shot 2021-09-01 at 10 30 18 PM" src="https://user-images.githubusercontent.com/1151048/131782069-b9ab959c-f22d-44d5-baf0-561fe349c037.png">

To test the manual exclusions of any other problematic fields, create any index which has runtime fields or `constant keywords` but does not have anything within the `_source` document using dev tools. For example you can use `constant keyword` like so

```json
PUT constant-keywords-deleme
{
  "mappings": {
    "dynamic": "strict",
    "properties": {
      "@timestamp": {
        "type": "date"
      },
      "testing_ignored": {
        "properties": {
          "constant": {
            "type": "constant_keyword",
            "value": "constant_value"
          }
        }
      },
      "testing_regex": {
        "type": "constant_keyword",
        "value": "constant_value"
      },
      "normal_constant": {
        "type": "constant_keyword",
        "value": "constant_value"
      },
      "small_field": {
        "type": "keyword",
        "ignore_above": 10
      }
    }
  }
}

PUT constant-keywords-deleme/_doc/1
{
  "@timestamp": "2021-09-02T04:20:01.760Z"
}
```

Set in your `kibana.yml` the key/value of:

```yml
xpack.securitySolution.alertIgnoreFields: ['testing_ignored.constant', '/.*_regex/']
```

Setup a rule to run:
<img width="1083" alt="Screen Shot 2021-09-01 at 10 23 23 PM" src="https://user-images.githubusercontent.com/1151048/131781696-fea0d421-836f-465c-9be6-5289fbb622a4.png">

Once it runs you should notice that the constant values for testing are not on the signals table since it only typically exists in the fields API:
<img width="1166" alt="Screen Shot 2021-09-01 at 10 26 16 PM" src="https://user-images.githubusercontent.com/1151048/131781782-1684fb1d-bed9-4cf0-be9a-0abe1f0f34d1.png">

But the normal one still exists:
<img width="1136" alt="Screen Shot 2021-09-01 at 10 26 31 PM" src="https://user-images.githubusercontent.com/1151048/131781827-5450c693-de9e-4285-b082-9f7a2cbd5d07.png">

If you change the `xpack.securitySolution.alertIgnoreFields` by removing it and re-generate the signals you will see these values added back.

### Checklist

Delete any items that are not applicable to this PR.

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios
- [x] If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the [docker list](https://github.com/elastic/kibana/blob/master/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)

# Conflicts:
#	src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/create_security_rule_type_factory.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/factories/utils/build_bulk_body.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/factories/wrap_hits_factory.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/indicator_match/create_indicator_match_alert_type.test.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/indicator_match/create_indicator_match_alert_type.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/ml/create_ml_alert_type.test.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/ml/create_ml_alert_type.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/query/create_query_alert_type.test.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/query/create_query_alert_type.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/rule_types/types.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/build_bulk_body.test.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/build_bulk_body.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/signal_rule_alert_type.test.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/signal_rule_alert_type.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/wrap_hits_factory.ts
#	x-pack/plugins/security_solution/server/lib/detection_engine/signals/wrap_sequences_factory.ts
#	x-pack/plugins/security_solution/server/plugin.ts
#	x-pack/test/detection_engine_api_integration/security_and_spaces/tests/index.ts

src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker

@@ -387,6 +387,7 @@ kibana_vars=(
     xpack.security.sessionTimeout
     xpack.securitySolution.alertMergeStrategy
     xpack.securitySolution.alertResultListDefaultDateRange
+    xpack.securitySolution.alertIgnoreFields
     xpack.securitySolution.endpointResultListDefaultFirstPageIndex
     xpack.securitySolution.endpointResultListDefaultPageSize
     xpack.securitySolution.maxRuleImportExportSize

x-pack/plugins/security_solution/server/config.test.ts

@@ -0,0 +1,80 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { configSchema } from './config';
+
+describe('config', () => {
+  describe('alertIgnoreFields', () => {
+    test('should default to an empty array', () => {
+      expect(configSchema.validate({}).alertIgnoreFields).toEqual([]);
+    });
+
+    test('should accept an array of strings', () => {
+      expect(
+        configSchema.validate({ alertIgnoreFields: ['foo.bar', 'mars.bar'] }).alertIgnoreFields
+      ).toEqual(['foo.bar', 'mars.bar']);
+    });
+
+    test('should throw if a non string is being sent in', () => {
+      expect(
+        () =>
+          configSchema.validate({
+            alertIgnoreFields: 5,
+          }).alertIgnoreFields
+      ).toThrow('[alertIgnoreFields]: expected value of type [array] but got [number]');
+    });
+
+    test('should throw if we send in an invalid regular expression as a string', () => {
+      expect(
+        () =>
+          configSchema.validate({
+            alertIgnoreFields: ['/(/'],
+          }).alertIgnoreFields
+      ).toThrow(
+        '[alertIgnoreFields]: "Invalid regular expression: /(/: Unterminated group" at array position 0'
+      );
+    });
+
+    test('should throw with two errors if we send two invalid regular expressions', () => {
+      expect(
+        () =>
+          configSchema.validate({
+            alertIgnoreFields: ['/(/', '/(invalid/'],
+          }).alertIgnoreFields
+      ).toThrow(
+        '[alertIgnoreFields]: "Invalid regular expression: /(/: Unterminated group" at array position 0. "Invalid regular expression: /(invalid/: Unterminated group" at array position 1'
+      );
+    });
+
+    test('should throw with two errors with a valid string mixed in if we send two invalid regular expressions', () => {
+      expect(
+        () =>
+          configSchema.validate({
+            alertIgnoreFields: ['/(/', 'valid.string', '/(invalid/'],
+          }).alertIgnoreFields
+      ).toThrow(
+        '[alertIgnoreFields]: "Invalid regular expression: /(/: Unterminated group" at array position 0. "Invalid regular expression: /(invalid/: Unterminated group" at array position 2'
+      );
+    });
+
+    test('should accept a valid regular expression within the string', () => {
+      expect(
+        configSchema.validate({
+          alertIgnoreFields: ['/(.*)/'],
+        }).alertIgnoreFields
+      ).toEqual(['/(.*)/']);
+    });
+
+    test('should accept two valid regular expressions', () => {
+      expect(
+        configSchema.validate({
+          alertIgnoreFields: ['/(.*)/', '/(.valid*)/'],
+        }).alertIgnoreFields
+      ).toEqual(['/(.*)/', '/(.valid*)/']);
+    });
+  });
+});

x-pack/plugins/security_solution/server/config.ts

@@ -21,12 +21,61 @@ export const configSchema = schema.object({
   maxRuleImportPayloadBytes: schema.number({ defaultValue: 10485760 }),
   maxTimelineImportExportSize: schema.number({ defaultValue: 10000 }),
   maxTimelineImportPayloadBytes: schema.number({ defaultValue: 10485760 }),
+
+  /**
+   * This is used within the merge strategies:
+   * server/lib/detection_engine/signals/source_fields_merging
+   *
+   * For determining which strategy for merging "fields" and "_source" together to get
+   * runtime fields, constant keywords, etc...
+   *
+   * "missingFields" (default) This will only merge fields that are missing from the _source and exist in the fields.
+   * "noFields" This will turn off all merging of runtime fields, constant keywords from fields.
+   * "allFields" This will merge and overwrite anything found within "fields" into "_source" before indexing the data.
+   */
   alertMergeStrategy: schema.oneOf(
     [schema.literal('allFields'), schema.literal('missingFields'), schema.literal('noFields')],
     {
       defaultValue: 'missingFields',
     }
   ),
+
+  /**
+   * This is used within the merge strategies:
+   * server/lib/detection_engine/signals/source_fields_merging
+   *
+   * For determining if we need to ignore particular "fields" and not merge them with "_source" such as
+   * runtime fields, constant keywords, etc...
+   *
+   * This feature and functionality is mostly as "safety feature" meaning that we have had bugs in the past
+   * where something down the stack unexpectedly ends up in the fields API which causes documents to not
+   * be indexable. Rather than changing alertMergeStrategy to be "noFields", you can use this array to add
+   * any problematic values.
+   *
+   * You can use plain dotted notation strings such as "host.name" or a regular expression such as "/host\..+/"
+   */
+  alertIgnoreFields: schema.arrayOf(schema.string(), {
+    defaultValue: [],
+    validate(ignoreFields) {
+      const errors = ignoreFields.flatMap((ignoreField, index) => {
+        if (ignoreField.startsWith('/') && ignoreField.endsWith('/')) {
+          try {
+            new RegExp(ignoreField.slice(1, -1));
+            return [];
+          } catch (error) {
+            return [`"${error.message}" at array position ${index}`];
+          }
+        } else {
+          return [];
+        }
+      });
+      if (errors.length !== 0) {
+        return errors.join('. ');
+      } else {
+        return undefined;
+      }
+    },
+  }),
   [SIGNALS_INDEX_KEY]: schema.string({ defaultValue: DEFAULT_SIGNALS_INDEX }),
 
   /**

x-pack/plugins/security_solution/server/lib/detection_engine/routes/__mocks__/index.ts

@@ -31,6 +31,7 @@ export const createMockConfig = (): ConfigType => ({
   packagerTaskInterval: '60s',
   validateArtifactDownloads: true,
   alertMergeStrategy: 'missingFields',
+  alertIgnoreFields: [],
   prebuiltRulesFromFileSystem: true,
   prebuiltRulesFromSavedObjects: false,
 });

x-pack/plugins/security_solution/server/lib/detection_engine/signals/build_bulk_body.test.ts

@@ -41,7 +41,8 @@ describe('buildBulkBody', () => {
     const fakeSignalSourceHit: SignalHitOptionalTimestamp = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     // Timestamp will potentially always be different so remove it for the test
     delete fakeSignalSourceHit['@timestamp'];
@@ -109,7 +110,8 @@ describe('buildBulkBody', () => {
     const fakeSignalSourceHit: SignalHitOptionalTimestamp = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     // Timestamp will potentially always be different so remove it for the test
     delete fakeSignalSourceHit['@timestamp'];
@@ -191,7 +193,8 @@ describe('buildBulkBody', () => {
     const fakeSignalSourceHit: SignalHitOptionalTimestamp = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     // Timestamp will potentially always be different so remove it for the test
     delete fakeSignalSourceHit['@timestamp'];
@@ -259,7 +262,8 @@ describe('buildBulkBody', () => {
     const fakeSignalSourceHit: SignalHitOptionalTimestamp = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     // Timestamp will potentially always be different so remove it for the test
     delete fakeSignalSourceHit['@timestamp'];
@@ -324,7 +328,8 @@ describe('buildBulkBody', () => {
     const fakeSignalSourceHit: SignalHitOptionalTimestamp = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     // Timestamp will potentially always be different so remove it for the test
     delete fakeSignalSourceHit['@timestamp'];
@@ -388,7 +393,8 @@ describe('buildBulkBody', () => {
     const { '@timestamp': timestamp, ...fakeSignalSourceHit } = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     const expected: Omit<SignalHit, '@timestamp'> & { someKey: string } = {
       someKey: 'someValue',
@@ -448,7 +454,8 @@ describe('buildBulkBody', () => {
     const { '@timestamp': timestamp, ...fakeSignalSourceHit } = buildBulkBody(
       ruleSO,
       doc,
-      'missingFields'
+      'missingFields',
+      []
     );
     const expected: Omit<SignalHit, '@timestamp'> & { someKey: string } = {
       someKey: 'someValue',
@@ -677,7 +684,8 @@ describe('buildSignalFromEvent', () => {
       ancestor,
       ruleSO,
       true,
-      'missingFields'
+      'missingFields',
+      []
     );
 
     // Timestamp will potentially always be different so remove it for the test

x-pack/plugins/security_solution/server/lib/detection_engine/signals/build_bulk_body.ts

@@ -35,9 +35,10 @@ import type { ConfigType } from '../../../config';
 export const buildBulkBody = (
   ruleSO: SavedObject<AlertAttributes>,
   doc: SignalSourceHit,
-  mergeStrategy: ConfigType['alertMergeStrategy']
+  mergeStrategy: ConfigType['alertMergeStrategy'],
+  ignoreFields: ConfigType['alertIgnoreFields']
 ): SignalHit => {
-  const mergedDoc = getMergeStrategy(mergeStrategy)({ doc });
+  const mergedDoc = getMergeStrategy(mergeStrategy)({ doc, ignoreFields });
   const rule = buildRuleWithOverrides(ruleSO, mergedDoc._source ?? {});
   const signal: Signal = {
     ...buildSignal([mergedDoc], rule),
@@ -68,11 +69,12 @@ export const buildSignalGroupFromSequence = (
   sequence: EqlSequence<SignalSource>,
   ruleSO: SavedObject<AlertAttributes>,
   outputIndex: string,
-  mergeStrategy: ConfigType['alertMergeStrategy']
+  mergeStrategy: ConfigType['alertMergeStrategy'],
+  ignoreFields: ConfigType['alertIgnoreFields']
 ): WrappedSignalHit[] => {
   const wrappedBuildingBlocks = wrapBuildingBlocks(
     sequence.events.map((event) => {
-      const signal = buildSignalFromEvent(event, ruleSO, false, mergeStrategy);
+      const signal = buildSignalFromEvent(event, ruleSO, false, mergeStrategy, ignoreFields);
       signal.signal.rule.building_block_type = 'default';
       return signal;
     }),
@@ -134,9 +136,10 @@ export const buildSignalFromEvent = (
   event: BaseSignalHit,
   ruleSO: SavedObject<AlertAttributes>,
   applyOverrides: boolean,
-  mergeStrategy: ConfigType['alertMergeStrategy']
+  mergeStrategy: ConfigType['alertMergeStrategy'],
+  ignoreFields: ConfigType['alertIgnoreFields']
 ): SignalHit => {
-  const mergedEvent = getMergeStrategy(mergeStrategy)({ doc: event });
+  const mergedEvent = getMergeStrategy(mergeStrategy)({ doc: event, ignoreFields });
   const rule = applyOverrides
     ? buildRuleWithOverrides(ruleSO, mergedEvent._source ?? {})
     : buildRuleWithoutOverrides(ruleSO);

x-pack/plugins/security_solution/server/lib/detection_engine/signals/search_after_bulk_create.test.ts

@@ -71,6 +71,7 @@ describe('searchAfterAndBulkCreate', () => {
       ruleSO,
       signalsIndex: DEFAULT_SIGNALS_INDEX,
       mergeStrategy: 'missingFields',
+      ignoreFields: [],
     });
   });
 

x-pack/plugins/security_solution/server/lib/detection_engine/signals/signal_rule_alert_type.test.ts

@@ -194,6 +194,7 @@ describe('signal_rule_alert_type', () => {
       ml: mlMock,
       lists: listMock.createSetup(),
       mergeStrategy: 'missingFields',
+      ignoreFields: [],
     });
   });
 

x-pack/plugins/security_solution/server/lib/detection_engine/signals/signal_rule_alert_type.ts

@@ -77,13 +77,15 @@ export const signalRulesAlertType = ({
   ml,
   lists,
   mergeStrategy,
+  ignoreFields,
 }: {
   logger: Logger;
   eventsTelemetry: TelemetryEventsSender | undefined;
   version: string;
   ml: SetupPlugins['ml'];
   lists: SetupPlugins['lists'] | undefined;
   mergeStrategy: ConfigType['alertMergeStrategy'];
+  ignoreFields: ConfigType['alertIgnoreFields'];
 }): SignalRuleAlertTypeDefinition => {
   return {
     id: SIGNALS_ID,
@@ -237,12 +239,14 @@ export const signalRulesAlertType = ({
           ruleSO: savedObject,
           signalsIndex: params.outputIndex,
           mergeStrategy,
+          ignoreFields,
         });
 
         const wrapSequences = wrapSequencesFactory({
           ruleSO: savedObject,
           signalsIndex: params.outputIndex,
           mergeStrategy,
+          ignoreFields,
         });
 
         if (isMlRule(type)) {