vault/builtin/audit/file/backend.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

package file

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

	"github.com/hashicorp/eventlogger"
	"github.com/hashicorp/vault/audit"
	"github.com/hashicorp/vault/internal/observability/event"
	"github.com/hashicorp/vault/sdk/helper/salt"
	"github.com/hashicorp/vault/sdk/logical"
)

const (
	stdout  = "stdout"
	discard = "discard"
)

func Factory(ctx context.Context, conf *audit.BackendConfig, useEventLogger bool, headersConfig audit.HeaderFormatter) (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.EqualFold(path, stdout) {
		path = stdout
	}
	if strings.EqualFold(path, discard) {
		path = discard
	}

	var cfgOpts []audit.Option

	if format, ok := conf.Config["format"]; ok {
		cfgOpts = append(cfgOpts, audit.WithFormat(format))
	}

	// Check if hashing of accessor is disabled
	if hmacAccessorRaw, ok := conf.Config["hmac_accessor"]; ok {
		v, err := strconv.ParseBool(hmacAccessorRaw)
		if err != nil {
			return nil, err
		}
		cfgOpts = append(cfgOpts, audit.WithHMACAccessor(v))
	}

	// Check if raw logging is enabled
	if raw, ok := conf.Config["log_raw"]; ok {
		v, err := strconv.ParseBool(raw)
		if err != nil {
			return nil, err
		}
		cfgOpts = append(cfgOpts, audit.WithRaw(v))
	}

	if elideListResponsesRaw, ok := conf.Config["elide_list_responses"]; ok {
		v, err := strconv.ParseBool(elideListResponsesRaw)
		if err != nil {
			return nil, err
		}
		cfgOpts = append(cfgOpts, audit.WithElision(v))
	}

	mode := os.FileMode(0o600)
	if modeRaw, ok := conf.Config["mode"]; ok {
		m, err := strconv.ParseUint(modeRaw, 8, 32)
		if err != nil {
			return nil, err
		}
		switch m {
		case 0:
			// if mode is 0000, then do not modify file mode
			if path != stdout && path != discard {
				fileInfo, err := os.Stat(path)
				if err != nil {
					return nil, err
				}
				mode = fileInfo.Mode()
			}
		default:
			mode = os.FileMode(m)
		}
	}

	cfg, err := audit.NewFormatterConfig(cfgOpts...)
	if err != nil {
		return nil, err
	}

	b := &Backend{
		path:         path,
		mode:         mode,
		saltConfig:   conf.SaltConfig,
		saltView:     conf.SaltView,
		salt:         new(atomic.Value),
		formatConfig: cfg,
	}

	// Ensure we are working with the right type by explicitly storing a nil of
	// the right type
	b.salt.Store((*salt.Salt)(nil))

	// Configure the formatter for either case.
	f, err := audit.NewEntryFormatter(b.formatConfig, b, audit.WithHeaderFormatter(headersConfig), audit.WithPrefix(conf.Config["prefix"]))
	if err != nil {
		return nil, fmt.Errorf("error creating formatter: %w", err)
	}
	var w audit.Writer
	switch b.formatConfig.RequiredFormat {
	case audit.JSONFormat:
		w = &audit.JSONWriter{Prefix: conf.Config["prefix"]}
	case audit.JSONxFormat:
		w = &audit.JSONxWriter{Prefix: conf.Config["prefix"]}
	default:
		return nil, fmt.Errorf("unknown format type %q", b.formatConfig.RequiredFormat)
	}

	fw, err := audit.NewEntryFormatterWriter(b.formatConfig, f, w)
	if err != nil {
		return nil, fmt.Errorf("error creating formatter writer: %w", err)
	}
	b.formatter = fw

	if useEventLogger {
		b.nodeIDList = make([]eventlogger.NodeID, 2)
		b.nodeMap = make(map[eventlogger.NodeID]eventlogger.Node)

		formatterNodeID, err := event.GenerateNodeID()
		if err != nil {
			return nil, fmt.Errorf("error generating random NodeID for formatter node: %w", err)
		}

		b.nodeIDList[0] = formatterNodeID
		b.nodeMap[formatterNodeID] = f

		var sinkNode eventlogger.Node

		switch path {
		case stdout:
			sinkNode = &audit.SinkWrapper{Name: path, Sink: event.NewStdoutSinkNode(b.formatConfig.RequiredFormat.String())}
		case discard:
			sinkNode = &audit.SinkWrapper{Name: path, Sink: event.NewNoopSink()}
		default:
			var err error

			var opts []event.Option
			// Check if mode is provided
			if modeRaw, ok := conf.Config["mode"]; ok {
				opts = append(opts, event.WithFileMode(modeRaw))
			}

			// The NewFileSink function attempts to open the file and will
			// return an error if it can't.
			n, err := event.NewFileSink(
				b.path,
				b.formatConfig.RequiredFormat.String(), opts...)
			if err != nil {
				return nil, fmt.Errorf("file sink creation failed for path %q: %w", path, err)
			}
			sinkNode = &audit.SinkWrapper{Name: conf.MountPath, Sink: n}
		}

		sinkNodeID, err := event.GenerateNodeID()
		if err != nil {
			return nil, fmt.Errorf("error generating random NodeID for sink node: %w", err)
		}

		b.nodeIDList[1] = sinkNodeID
		b.nodeMap[sinkNodeID] = sinkNode
	} else {
		switch path {
		case stdout:
		case discard:
		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 %q for writing: %w", 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.EntryFormatterWriter
	formatConfig audit.FormatterConfig

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

	saltMutex  sync.RWMutex
	salt       *atomic.Value
	saltConfig *salt.Config
	saltView   logical.Storage

	nodeIDList []eventlogger.NodeID
	nodeMap    map[eventlogger.NodeID]eventlogger.Node
}

var _ audit.Backend = (*Backend)(nil)

func (b *Backend) Salt(ctx context.Context) (*salt.Salt, error) {
	s := b.salt.Load().(*salt.Salt)
	if s != nil {
		return s, nil
	}

	b.saltMutex.Lock()
	defer b.saltMutex.Unlock()

	s = b.salt.Load().(*salt.Salt)
	if s != nil {
		return s, nil
	}

	newSalt, err := salt.NewSalt(ctx, b.saltView, b.saltConfig)
	if err != nil {
		b.salt.Store((*salt.Salt)(nil))
		return nil, err
	}

	b.salt.Store(newSalt)
	return newSalt, nil
}

func (b *Backend) LogRequest(ctx context.Context, in *logical.LogInput) error {
	var writer io.Writer
	switch b.path {
	case stdout:
		writer = os.Stdout
	case discard:
		return nil
	}

	buf := bytes.NewBuffer(make([]byte, 0, 2000))
	err := b.formatter.FormatAndWriteRequest(ctx, buf, in)
	if err != nil {
		return err
	}

	return b.log(ctx, buf, writer)
}

func (b *Backend) log(_ context.Context, buf *bytes.Buffer, writer io.Writer) error {
	reader := bytes.NewReader(buf.Bytes())

	b.fileLock.Lock()

	if writer == nil {
		if err := b.open(); err != nil {
			b.fileLock.Unlock()
			return err
		}
		writer = b.f
	}

	if _, err := reader.WriteTo(writer); err == nil {
		b.fileLock.Unlock()
		return nil
	} else if b.path == stdout {
		b.fileLock.Unlock()
		return err
	}

	// If writing to stdout there's no real reason to think anything would have
	// changed so return above. Otherwise, opportunistically try to re-open the
	// FD, once per call.
	b.f.Close()
	b.f = nil

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

	reader.Seek(0, io.SeekStart)
	_, err := reader.WriteTo(writer)
	b.fileLock.Unlock()
	return err
}

func (b *Backend) LogResponse(ctx context.Context, in *logical.LogInput) error {
	var writer io.Writer
	switch b.path {
	case stdout:
		writer = os.Stdout
	case discard:
		return nil
	}

	buf := bytes.NewBuffer(make([]byte, 0, 6000))
	err := b.formatter.FormatAndWriteResponse(ctx, buf, in)
	if err != nil {
		return err
	}

	return b.log(ctx, buf, writer)
}

func (b *Backend) LogTestMessage(ctx context.Context, in *logical.LogInput, config map[string]string) error {
	// Event logger behavior - manually Process each node
	if len(b.nodeIDList) > 0 {
		return audit.ProcessManual(ctx, in, b.nodeIDList, b.nodeMap)
	}

	// Old behavior
	var writer io.Writer
	switch b.path {
	case stdout:
		writer = os.Stdout
	case discard:
		return nil
	}

	var buf bytes.Buffer

	temporaryFormatter, err := audit.NewTemporaryFormatter(config["format"], config["prefix"])
	if err != nil {
		return err
	}

	if err = temporaryFormatter.FormatAndWriteRequest(ctx, &buf, in); err != nil {
		return err
	}

	return b.log(ctx, &buf, writer)
}

// 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 {
	// When there are nodes created in the map, use the eventlogger behavior.
	if len(b.nodeMap) > 0 {
		for _, n := range b.nodeMap {
			if n.Type() == eventlogger.NodeTypeSink {
				return n.Reopen()
			}
		}

		return nil
	} else {
		// old non-eventlogger behavior
		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.Store((*salt.Salt)(nil))
}

// RegisterNodesAndPipeline registers the nodes and a pipeline as required by
// the audit.Backend interface.
func (b *Backend) RegisterNodesAndPipeline(broker *eventlogger.Broker, name string) error {
	for id, node := range b.nodeMap {
		if err := broker.RegisterNode(id, node); err != nil {
			return err
		}
	}

	pipeline := eventlogger.Pipeline{
		PipelineID: eventlogger.PipelineID(name),
		EventType:  eventlogger.EventType("audit"),
		NodeIDs:    b.nodeIDList,
	}

	return broker.RegisterPipeline(pipeline)
}