Osquerybeat: Improve handling of osquery.autoload file, allow customi…

…zations (elastic#28289)

Previously the osquery.autoload file was overwritten every time on
osquerybeat start and stamped with our extension.
After the change we check the content of the file and do not overwrite it on
each osquerybeat start. This allows the user to deploy their own
extensions if their want and start osquery with that.

x-pack/osquerybeat/internal/osqd/osqueryd.go

@@ -5,6 +5,7 @@
 package osqd
 
 import (
+	"bufio"
 	"context"
 	"fmt"
 	"io"
@@ -263,8 +264,9 @@ func (q *OSQueryD) prepare(ctx context.Context) (func(), error) {
 
 	// Write the autoload file
 	extensionAutoloadPath := q.resolveDataPath(osqueryAutoload)
-	if err := ioutil.WriteFile(extensionAutoloadPath, []byte(extensionPath), 0644); err != nil {
-		return nil, errors.Wrap(err, "failed write osquery extension autoload file")
+	err = prepareAutoloadFile(extensionAutoloadPath, extensionPath, q.log)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to prepare extensions autoload file")
 	}
 
 	// Write the flagsfile in order to lock down/prevent loading default flags from osquery global locations.
@@ -286,6 +288,60 @@ func (q *OSQueryD) prepare(ctx context.Context) (func(), error) {
 	return func() {}, nil
 }
 
+func prepareAutoloadFile(extensionAutoloadPath, mandatoryExtensionPath string, log *logp.Logger) error {
+	ok, err := fileutil.FileExists(extensionAutoloadPath)
+	if err != nil {
+		return errors.Wrapf(err, "failed to check osquery.autoload file exists")
+	}
+
+	rewrite := false
+
+	if ok {
+		log.Debugf("Extensions autoload file %s exists, verify the first extension is ours", extensionAutoloadPath)
+		err = verifyAutoloadFile(extensionAutoloadPath, mandatoryExtensionPath)
+		if err != nil {
+			log.Debugf("Extensions autoload file %v verification failed, err: %v, create a new one", extensionAutoloadPath, err)
+			rewrite = true
+		}
+	} else {
+		log.Debugf("Extensions autoload file %s doesn't exists, create a new one", extensionAutoloadPath)
+		rewrite = true
+	}
+
+	if rewrite {
+		if err := ioutil.WriteFile(extensionAutoloadPath, []byte(mandatoryExtensionPath), 0644); err != nil {
+			return errors.Wrap(err, "failed write osquery extension autoload file")
+		}
+	}
+	return nil
+}
+
+func verifyAutoloadFile(extensionAutoloadPath, mandatoryExtensionPath string) error {
+	f, err := os.Open(extensionAutoloadPath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	scanner := bufio.NewScanner(f)
+	for i := 0; scanner.Scan(); i++ {
+		line := scanner.Text()
+		if i == 0 {
+			// Check that the first line is the mandatory extension
+			if line != mandatoryExtensionPath {
+				return errors.New("extentsions autoload file is missing mandatory extension in the first line of the file")
+			}
+		}
+
+		// Check that the line contains the valid path that exists
+		_, err := os.Stat(line)
+		if err != nil {
+			return err
+		}
+	}
+
+	return scanner.Err()
+}
+
 func (q *OSQueryD) prepareBinPath() error {
 	// If path to osquery was not set use the current executable path
 	if q.binPath == "" {

x-pack/osquerybeat/internal/osqd/osqueryd_test.go

@@ -5,8 +5,18 @@
 package osqd
 
 import (
+	"bufio"
+	"errors"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"testing"
 
+	"github.com/elastic/beats/v7/libbeat/common"
+	"github.com/elastic/beats/v7/libbeat/logp"
+	"github.com/elastic/beats/v7/x-pack/osquerybeat/internal/fileutil"
+
+	"github.com/gofrs/uuid"
 	"github.com/google/go-cmp/cmp"
 )
 
@@ -46,3 +56,120 @@ func TestNew(t *testing.T) {
 		t.Error(diff)
 	}
 }
+
+func TestVerifyAutoloadFileMissing(t *testing.T) {
+	dir := uuid.Must(uuid.NewV4()).String()
+	extensionAutoloadPath := filepath.Join(dir, osqueryAutoload)
+	mandatoryExtensionPath := filepath.Join(dir, extensionName)
+	err := verifyAutoloadFile(extensionAutoloadPath, mandatoryExtensionPath)
+	if !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("expected error: %v, got: %v", os.ErrNotExist, err)
+	}
+}
+
+// TestPrepareAutoloadFile tests possibly different states of the osquery.autoload file and that it is restored into the workable state
+func TestPrepareAutoloadFile(t *testing.T) {
+	validLogger := logp.NewLogger("osqueryd_test")
+
+	// Prepare the directory with extension
+	dir, err := os.MkdirTemp("", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+	mandatoryExtensionPath := filepath.Join(dir, extensionName)
+
+	// Write fake extension file for testing
+	err = ioutil.WriteFile(mandatoryExtensionPath, nil, 0644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	randomContent := func(sz int) []byte {
+		b, err := common.RandomBytes(sz)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return b
+	}
+
+	tests := []struct {
+		Name        string
+		FileContent []byte
+	}{
+		{
+			Name:        "Empty file",
+			FileContent: nil,
+		},
+		{
+			Name:        "File with mandatory extension",
+			FileContent: []byte(mandatoryExtensionPath),
+		},
+		{
+			Name:        "Missing mandatory extension, should restore the file",
+			FileContent: []byte(filepath.Join(dir, "foobar.ext")),
+		},
+		{
+			Name:        "User extension path doesn't exists",
+			FileContent: []byte(mandatoryExtensionPath + "\n" + filepath.Join(dir, "foobar.ext")),
+		},
+		{
+			Name:        "Random garbage",
+			FileContent: randomContent(1234),
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.Name, func(t *testing.T) {
+
+			// Setup
+			dir, err := os.MkdirTemp("", "")
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			defer os.RemoveAll(dir)
+
+			extensionAutoloadPath := filepath.Join(dir, osqueryAutoload)
+
+			err = ioutil.WriteFile(extensionAutoloadPath, tc.FileContent, 0644)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			err = prepareAutoloadFile(extensionAutoloadPath, mandatoryExtensionPath, validLogger)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// Check the content, should have our mandatory extension and possibly the other extension paths with each extension existing on the disk
+			f, err := os.Open(extensionAutoloadPath)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer f.Close()
+			scanner := bufio.NewScanner(f)
+			for i := 0; scanner.Scan(); i++ {
+				line := scanner.Text()
+				if i == 0 {
+					if line != mandatoryExtensionPath {
+						t.Fatalf("expected the fist line of the file to be: %v , got: %v", mandatoryExtensionPath, line)
+					}
+				}
+				// Check that it is a valid path to the file on the disk
+				ok, err := fileutil.FileExists(line)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if !ok {
+					t.Fatalf("expected to have only valid paths to the extensions files that exists, got: %v", line)
+				}
+			}
+
+			err = scanner.Err()
+			if err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}