[add_session_metadata processor] Keep exited processes in the process…

… DB (#39173) (#39225)

With the add_session_metadata processor, don't remove processes from the process db when the process has exited.

The processor can be run on an fork/exec events after the process has actually exited, so the process must remain in the DB after it has exited, so the info can be used in enrichment of these events.

Now that the process is kept in the DB, the exit code is also appended on exit events, so the exit code can be used in enrichment of the exit events.

(cherry picked from commit 9649588)

Co-authored-by: Michael Wolf <michael.wolf@elastic.co>

CHANGELOG.next.asciidoc

@@ -94,6 +94,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 
 *Auditbeat*
 - Set field types to correctly match ECS in sessionmd processor {issue}38955[38955] {pull}38994[38994]
+- Keep process info on exited processes, to avoid failing to enrich events in sessionmd processor {pull}39173[39173]
 
 *Filebeat*
 

x-pack/auditbeat/processors/sessionmd/add_session_metadata.go

@@ -57,7 +57,7 @@ func New(cfg *cfg.C) (beat.Processor, error) {
 	}
 
 	backfilledPIDs := db.ScrapeProcfs()
-	logger.Debugf("backfilled %d processes", len(backfilledPIDs))
+	logger.Infof("backfilled %d processes", len(backfilledPIDs))
 
 	var p provider.Provider
 
@@ -70,6 +70,9 @@ func New(cfg *cfg.C) (beat.Processor, error) {
 			if err != nil {
 				return nil, fmt.Errorf("failed to create provider: %w", err)
 			}
+			logger.Info("backend=auto using procfs")
+		} else {
+			logger.Info("backend=auto using ebpf")
 		}
 	case "ebpf":
 		p, err = ebpf_provider.NewProvider(ctx, logger, db)
@@ -111,6 +114,11 @@ func (p *addSessionMetadata) Run(ev *beat.Event) (*beat.Event, error) {
 	return result, nil
 }
 
+func (p *addSessionMetadata) Close() error {
+	p.db.Close()
+	return nil
+}
+
 func (p *addSessionMetadata) String() string {
 	return fmt.Sprintf("%v=[backend=%s, pid_field=%s]",
 		processorName, p.config.Backend, p.config.PIDField)

x-pack/auditbeat/processors/sessionmd/processdb/db.go

@@ -7,6 +7,7 @@
 package processdb
 
 import (
+	"container/heap"
 	"encoding/base64"
 	"errors"
 	"fmt"
@@ -82,6 +83,7 @@ type Process struct {
 	Cwd      string
 	Env      map[string]string
 	Filename string
+	ExitCode int32
 }
 
 var (
@@ -185,20 +187,26 @@ type DB struct {
 	entryLeaders             map[uint32]EntryType
 	entryLeaderRelationships map[uint32]uint32
 	procfs                   procfs.Reader
+	stopChan                 chan struct{}
+	removalCandidates        rcHeap
 }
 
 func NewDB(reader procfs.Reader, logger logp.Logger) (*DB, error) {
 	once.Do(initialize)
 	if initError != nil {
 		return &DB{}, initError
 	}
-	return &DB{
+	db := DB{
 		logger:                   logp.NewLogger("processdb"),
 		processes:                make(map[uint32]Process),
 		entryLeaders:             make(map[uint32]EntryType),
 		entryLeaderRelationships: make(map[uint32]uint32),
 		procfs:                   reader,
-	}, nil
+		stopChan:                 make(chan struct{}),
+		removalCandidates:        make(rcHeap, 0),
+	}
+	db.startReaper()
+	return &db, nil
 }
 
 func (db *DB) calculateEntityIDv1(pid uint32, startTime time.Time) string {
@@ -406,9 +414,18 @@ func (db *DB) InsertExit(exit types.ProcessExitEvent) {
 	defer db.mutex.Unlock()
 
 	pid := exit.PIDs.Tgid
-	delete(db.processes, pid)
-	delete(db.entryLeaders, pid)
-	delete(db.entryLeaderRelationships, pid)
+	process, ok := db.processes[pid]
+	if !ok {
+		db.logger.Errorf("could not insert exit, pid %v not found in db", pid)
+		return
+	}
+	process.ExitCode = exit.ExitCode
+	db.processes[pid] = process
+	heap.Push(&db.removalCandidates, removalCandidate{
+		pid:       pid,
+		startTime: process.PIDs.StartTimeNS,
+		exitTime:  time.Now(),
+	})
 }
 
 func interactiveFromTTY(tty types.TTYDev) bool {
@@ -437,6 +454,7 @@ func fullProcessFromDBProcess(p Process) types.Process {
 	ret.Thread.Capabilities.Effective, _ = capabilities.FromUint64(p.Creds.CapEffective)
 	ret.TTY.CharDevice.Major = p.CTTY.Major
 	ret.TTY.CharDevice.Minor = p.CTTY.Minor
+	ret.ExitCode = p.ExitCode
 
 	return ret
 }
@@ -716,3 +734,7 @@ func (db *DB) scrapeAncestors(proc Process) {
 		db.insertProcess(p)
 	}
 }
+
+func (db *DB) Close() {
+	close(db.stopChan)
+}