Fix where agent panics on nil event (#409)

google_guest_agent/events/sshtrustedca/sshtrustedca_linux.go

@@ -20,6 +20,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -78,7 +79,7 @@ func (mp *Watcher) setWaitingWrite(val bool) {
 
 // Run listens to ssh_trusted_ca's pipe open calls and report back the event.
 func (mp *Watcher) Run(ctx context.Context, evType string) (bool, interface{}, error) {
-	var canceled bool
+	var canceled atomic.Bool
 
 	for mp.isWaitingWrite() {
 		time.Sleep(10 * time.Millisecond)
@@ -95,7 +96,7 @@ func (mp *Watcher) Run(ctx context.Context, evType string) (bool, interface{}, e
 		case <-cancelContext:
 			break
 		case <-ctx.Done():
-			canceled = true
+			canceled.Store(true)
 
 			// Open the pipe as O_RDONLY to release the blocking open O_WRONLY.
 			pipeFile, err := os.OpenFile(mp.pipePath, os.O_RDONLY, 0644)
@@ -127,7 +128,7 @@ func (mp *Watcher) Run(ctx context.Context, evType string) (bool, interface{}, e
 
 	// Have we got a ctx.Done()? if so lets just return from here and unregister
 	// the watcher.
-	if canceled {
+	if canceled.Load() {
 		if err := pipeFile.Close(); err != nil {
 			logger.Errorf("Failed to close readonly pipe: %+v", err)
 		}

google_guest_agent/sshca/sshca.go

@@ -63,7 +63,12 @@ func writeFile(ctx context.Context, evType string, data interface{}, evData *eve
 	}
 
 	// Make sure we close the pipe after we've done writing to it.
-	pipeData := evData.Data.(*sshtrustedca.PipeData)
+	pipeData, ok := evData.Data.(*sshtrustedca.PipeData)
+	if !ok {
+		logger.Errorf("Received invalid event data (%+v), ignoring this event and un-subscribing %s", evData.Data, evType)
+		return false
+	}
+
 	defer func() {
 		if err := pipeData.File.Close(); err != nil {
 			logger.Errorf("Failed to close pipe: %+v", err)