backend.go

package file

import (
	"context"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"

	"github.com/hashicorp/vault/audit"
	"github.com/hashicorp/vault/helper/salt"
	"github.com/hashicorp/vault/logical"
)

func Factory(ctx context.Context, conf *audit.BackendConfig) (audit.Backend, error) {
	if conf.SaltConfig == nil {
		return nil, fmt.Errorf("nil salt config")
	}
	if conf.SaltView == nil {
		return nil, fmt.Errorf("nil salt view")
	}

	path, ok := conf.Config["file_path"]
	if !ok {
		path, ok = conf.Config["path"]
		if !ok {
			return nil, fmt.Errorf("file_path is required")
		}
	}

	// normalize path if configured for stdout
	if strings.ToLower(path) == "stdout" {
		path = "stdout"
	}
	if strings.ToLower(path) == "discard" {
		path = "discard"
	}

	format, ok := conf.Config["format"]
	if !ok {
		format = "json"
	}
	switch format {
	case "json", "jsonx":
	default:
		return nil, fmt.Errorf("unknown format type %s", format)
	}

	// Check if hashing of accessor is disabled
	hmacAccessor := true
	if hmacAccessorRaw, ok := conf.Config["hmac_accessor"]; ok {
		value, err := strconv.ParseBool(hmacAccessorRaw)
		if err != nil {
			return nil, err
		}
		hmacAccessor = value
	}

	// Check if raw logging is enabled
	logRaw := false
	if raw, ok := conf.Config["log_raw"]; ok {
		b, err := strconv.ParseBool(raw)
		if err != nil {
			return nil, err
		}
		logRaw = b
	}

	// Check if mode is provided
	mode := os.FileMode(0600)
	if modeRaw, ok := conf.Config["mode"]; ok {
		m, err := strconv.ParseUint(modeRaw, 8, 32)
		if err != nil {
			return nil, err
		}
		if m != 0 {
			mode = os.FileMode(m)
		}
	}

	b := &Backend{
		path:       path,
		mode:       mode,
		saltConfig: conf.SaltConfig,
		saltView:   conf.SaltView,
		formatConfig: audit.FormatterConfig{
			Raw:          logRaw,
			HMACAccessor: hmacAccessor,
		},
	}

	switch format {
	case "json":
		b.formatter.AuditFormatWriter = &audit.JSONFormatWriter{
			Prefix:   conf.Config["prefix"],
			SaltFunc: b.Salt,
		}
	case "jsonx":
		b.formatter.AuditFormatWriter = &audit.JSONxFormatWriter{
			Prefix:   conf.Config["prefix"],
			SaltFunc: b.Salt,
		}
	}

	switch path {
	case "stdout", "discard":
		// no need to test opening file if outputting to stdout or discarding
	default:
		// Ensure that the file can be successfully opened for writing;
		// otherwise it will be too late to catch later without problems
		// (ref: https://github.com/hashicorp/vault/issues/550)
		if err := b.open(); err != nil {
			return nil, fmt.Errorf("sanity check failed; unable to open %s for writing: %v", path, err)
		}
	}

	return b, nil
}

// Backend is the audit backend for the file-based audit store.
//
// NOTE: This audit backend is currently very simple: it appends to a file.
// It doesn't do anything more at the moment to assist with rotation
// or reset the write cursor, this should be done in the future.
type Backend struct {
	path string

	formatter    audit.AuditFormatter
	formatConfig audit.FormatterConfig

	fileLock sync.RWMutex
	f        *os.File
	mode     os.FileMode

	saltMutex  sync.RWMutex
	salt       *salt.Salt
	saltConfig *salt.Config
	saltView   logical.Storage
}

func (b *Backend) Salt() (*salt.Salt, error) {
	b.saltMutex.RLock()
	if b.salt != nil {
		defer b.saltMutex.RUnlock()
		return b.salt, nil
	}
	b.saltMutex.RUnlock()
	b.saltMutex.Lock()
	defer b.saltMutex.Unlock()
	if b.salt != nil {
		return b.salt, nil
	}
	salt, err := salt.NewSalt(b.saltView, b.saltConfig)
	if err != nil {
		return nil, err
	}
	b.salt = salt
	return salt, nil
}

func (b *Backend) GetHash(data string) (string, error) {
	salt, err := b.Salt()
	if err != nil {
		return "", err
	}
	return audit.HashString(salt, data), nil
}

func (b *Backend) LogRequest(
	_ context.Context,
	auth *logical.Auth,
	req *logical.Request,
	outerErr error) error {

	b.fileLock.Lock()
	defer b.fileLock.Unlock()

	switch b.path {
	case "stdout":
		return b.formatter.FormatRequest(os.Stdout, b.formatConfig, auth, req, outerErr)
	case "discard":
		return b.formatter.FormatRequest(ioutil.Discard, b.formatConfig, auth, req, outerErr)
	}

	if err := b.open(); err != nil {
		return err
	}

	if err := b.formatter.FormatRequest(b.f, b.formatConfig, auth, req, outerErr); err == nil {
		return nil
	}

	// Opportunistically try to re-open the FD, once per call
	b.f.Close()
	b.f = nil

	if err := b.open(); err != nil {
		return err
	}

	return b.formatter.FormatRequest(b.f, b.formatConfig, auth, req, outerErr)
}

func (b *Backend) LogResponse(
	_ context.Context,
	auth *logical.Auth,
	req *logical.Request,
	resp *logical.Response,
	err error) error {

	b.fileLock.Lock()
	defer b.fileLock.Unlock()

	switch b.path {
	case "stdout":
		return b.formatter.FormatResponse(os.Stdout, b.formatConfig, auth, req, resp, err)
	case "discard":
		return b.formatter.FormatResponse(ioutil.Discard, b.formatConfig, auth, req, resp, err)
	}

	if err := b.open(); err != nil {
		return err
	}

	if err := b.formatter.FormatResponse(b.f, b.formatConfig, auth, req, resp, err); err == nil {
		return nil
	}

	// Opportunistically try to re-open the FD, once per call
	b.f.Close()
	b.f = nil

	if err := b.open(); err != nil {
		return err
	}

	return b.formatter.FormatResponse(b.f, b.formatConfig, auth, req, resp, err)
}

// The file lock must be held before calling this
func (b *Backend) open() error {
	if b.f != nil {
		return nil
	}
	if err := os.MkdirAll(filepath.Dir(b.path), b.mode); err != nil {
		return err
	}

	var err error
	b.f, err = os.OpenFile(b.path, os.O_APPEND|os.O_WRONLY|os.O_CREATE, b.mode)
	if err != nil {
		return err
	}

	// Change the file mode in case the log file already existed. We special
	// case /dev/null since we can't chmod it and bypass if the mode is zero
	switch b.path {
	case "/dev/null":
	default:
		if b.mode != 0 {
			err = os.Chmod(b.path, b.mode)
			if err != nil {
				return err
			}
		}
	}

	return nil
}

func (b *Backend) Reload(_ context.Context) error {
	switch b.path {
	case "stdout", "discard":
		return nil
	}

	b.fileLock.Lock()
	defer b.fileLock.Unlock()

	if b.f == nil {
		return b.open()
	}

	err := b.f.Close()
	// Set to nil here so that even if we error out, on the next access open()
	// will be tried
	b.f = nil
	if err != nil {
		return err
	}

	return b.open()
}

func (b *Backend) Invalidate(_ context.Context) {
	b.saltMutex.Lock()
	defer b.saltMutex.Unlock()
	b.salt = nil
}