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audit_linux.go
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package auditd
import (
"fmt"
"os"
"strconv"
"strings"
"syscall"
"time"
"github.com/pkg/errors"
"github.com/elastic/beats/libbeat/common"
"github.com/elastic/beats/libbeat/logp"
"github.com/elastic/beats/libbeat/monitoring"
"github.com/elastic/beats/metricbeat/mb"
"github.com/elastic/beats/metricbeat/mb/parse"
"github.com/elastic/go-libaudit"
"github.com/elastic/go-libaudit/aucoalesce"
"github.com/elastic/go-libaudit/auparse"
)
const (
namespace = "auditd"
auditLocked = 2
unicast = "unicast"
multicast = "multicast"
)
var (
auditdMetrics = monitoring.Default.NewRegistry(moduleName)
lostMetric = monitoring.NewInt(auditdMetrics, "lost")
)
func init() {
mb.Registry.MustAddMetricSet(moduleName, metricsetName, New,
mb.DefaultMetricSet(),
mb.WithHostParser(parse.EmptyHostParser),
mb.WithNamespace(namespace),
)
}
// MetricSet listens for audit messages from the Linux kernel using a netlink
// socket. It buffers the messages to ensure ordering and then streams the
// output. MetricSet implements the mb.PushMetricSet interface, and therefore
// does not rely on polling.
type MetricSet struct {
mb.BaseMetricSet
config Config
client *libaudit.AuditClient
log *logp.Logger
}
// New constructs a new MetricSet.
func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
config := defaultConfig
if err := base.Module().UnpackConfig(&config); err != nil {
return nil, errors.Wrap(err, "failed to unpack the auditd config")
}
log := logp.NewLogger(moduleName)
_, _, kernel, _ := kernelVersion()
log.Infof("auditd module is running as euid=%v on kernel=%v", os.Geteuid(), kernel)
client, err := newAuditClient(&config, log)
if err != nil {
return nil, errors.Wrap(err, "failed to create audit client")
}
lostMetric.Set(0)
return &MetricSet{
BaseMetricSet: base,
client: client,
config: config,
log: log,
}, nil
}
func newAuditClient(c *Config, log *logp.Logger) (*libaudit.AuditClient, error) {
var err error
c.SocketType, err = determineSocketType(c, log)
if err != nil {
return nil, err
}
log.Infof("socket_type=%s will be used.", c.SocketType)
if c.SocketType == multicast {
return libaudit.NewMulticastAuditClient(nil)
}
return libaudit.NewAuditClient(nil)
}
// Run initializes the audit client and receives audit messages from the
// kernel until the reporter's done channel is closed.
func (ms *MetricSet) Run(reporter mb.PushReporterV2) {
defer ms.client.Close()
if err := ms.addRules(reporter); err != nil {
reporter.Error(err)
ms.log.Errorw("Failure adding audit rules", "error", err)
return
}
out, err := ms.receiveEvents(reporter.Done())
if err != nil {
reporter.Error(err)
ms.log.Errorw("Failure receiving audit events", "error", err)
return
}
for {
select {
case <-reporter.Done():
return
case msgs := <-out:
reporter.Event(buildMetricbeatEvent(msgs, ms.config))
}
}
}
func (ms *MetricSet) addRules(reporter mb.PushReporterV2) error {
rules, err := ms.config.rules()
if err != nil {
return errors.Wrap(err, "failed to add rules")
}
if len(rules) == 0 {
ms.log.Info("No audit_rules were specified.")
return nil
}
client, err := libaudit.NewAuditClient(nil)
if err != nil {
return errors.Wrap(err, "failed to create audit client for adding rules")
}
defer client.Close()
// Don't attempt to change configuration if audit rules are locked (enabled == 2).
// Will result in EPERM.
status, err := client.GetStatus()
if err != nil {
err = errors.Wrap(err, "failed to get audit status before adding rules")
reporter.Error(err)
return err
}
if status.Enabled == auditLocked {
return errors.New("Skipping rule configuration: Audit rules are locked")
}
// Delete existing rules.
n, err := client.DeleteRules()
if err != nil {
return errors.Wrap(err, "failed to delete existing rules")
}
ms.log.Infof("Deleted %v pre-existing audit rules.", n)
// Add rules from config.
var failCount int
for _, rule := range rules {
if err = client.AddRule(rule.data); err != nil {
// Treat rule add errors as warnings and continue.
err = errors.Wrapf(err, "failed to add audit rule '%v'", rule.flags)
reporter.Error(err)
ms.log.Warnw("Failure adding audit rule", "error", err)
failCount++
}
}
ms.log.Infof("Successfully added %d of %d audit rules.",
len(rules)-failCount, len(rules))
return nil
}
func (ms *MetricSet) initClient() error {
if ms.config.SocketType == "multicast" {
// This request will fail with EPERM if this process does not have
// CAP_AUDIT_CONTROL, but we will ignore the response. The user will be
// required to ensure that auditing is enabled if the process is only
// given CAP_AUDIT_READ.
err := ms.client.SetEnabled(true, libaudit.NoWait)
return errors.Wrap(err, "failed to enable auditing in the kernel")
}
// Unicast client initialization (requires CAP_AUDIT_CONTROL and that the
// process be in initial PID namespace).
status, err := ms.client.GetStatus()
if err != nil {
return errors.Wrap(err, "failed to get audit status")
}
ms.log.Infow("audit status from kernel at start", "audit_status", status)
if status.Enabled == auditLocked {
return errors.New("failed to configure: The audit system is locked")
}
if fm, _ := ms.config.failureMode(); status.Failure != fm {
if err = ms.client.SetFailure(libaudit.FailureMode(fm), libaudit.NoWait); err != nil {
return errors.Wrap(err, "failed to set audit failure mode in kernel")
}
}
if status.RateLimit != ms.config.RateLimit {
if err = ms.client.SetRateLimit(ms.config.RateLimit, libaudit.NoWait); err != nil {
return errors.Wrap(err, "failed to set audit rate limit in kernel")
}
}
if status.BacklogLimit != ms.config.BacklogLimit {
if err = ms.client.SetBacklogLimit(ms.config.BacklogLimit, libaudit.NoWait); err != nil {
return errors.Wrap(err, "failed to set audit backlog limit in kernel")
}
}
if status.Enabled == 0 {
if err = ms.client.SetEnabled(true, libaudit.NoWait); err != nil {
return errors.Wrap(err, "failed to enable auditing in the kernel")
}
}
if err := ms.client.WaitForPendingACKs(); err != nil {
return errors.Wrap(err, "failed to wait for ACKs")
}
if err := ms.client.SetPID(libaudit.WaitForReply); err != nil {
if errno, ok := err.(syscall.Errno); ok && errno == syscall.EEXIST && status.PID != 0 {
return fmt.Errorf("failed to set audit PID. An audit process is already running (PID %d)", status.PID)
}
return errors.Wrapf(err, "failed to set audit PID (current audit PID %d)", status.PID)
}
return nil
}
func (ms *MetricSet) receiveEvents(done <-chan struct{}) (<-chan []*auparse.AuditMessage, error) {
if err := ms.initClient(); err != nil {
return nil, err
}
out := make(chan []*auparse.AuditMessage, ms.config.StreamBufferQueueSize)
reassembler, err := libaudit.NewReassembler(int(ms.config.ReassemblerMaxInFlight), ms.config.ReassemblerTimeout, &stream{done, out})
if err != nil {
return nil, errors.Wrap(err, "failed to create Reassembler")
}
go maintain(done, reassembler)
go func() {
defer close(out)
defer reassembler.Close()
for {
raw, err := ms.client.Receive(false)
if err != nil {
continue
}
if filterRecordType(raw.Type) {
continue
}
if err := reassembler.Push(raw.Type, raw.Data); err != nil {
ms.log.Debugw("Dropping audit message",
"record_type", raw.Type,
"message", string(raw.Data),
"error", err)
continue
}
}
}()
return out, nil
}
// maintain periodically evicts timed-out events from the Reassembler. This
// function will block until the done channel is closed or the Reassembler is
// closed.
func maintain(done <-chan struct{}, reassembler *libaudit.Reassembler) {
tick := time.NewTicker(500 * time.Millisecond)
defer tick.Stop()
for {
select {
case <-done:
return
case <-tick.C:
if err := reassembler.Maintain(); err != nil {
return
}
}
}
}
func filterRecordType(typ auparse.AuditMessageType) bool {
// Messages from 1300-2999 are valid audit message types.
if typ < auparse.AUDIT_USER_AUTH || typ > auparse.AUDIT_LAST_USER_MSG2 {
return true
}
return false
}
func buildMetricbeatEvent(msgs []*auparse.AuditMessage, config Config) mb.Event {
auditEvent, err := aucoalesce.CoalesceMessages(msgs)
if err != nil {
// Add messages on error so that it's possible to debug the problem.
out := mb.Event{MetricSetFields: common.MapStr{}}
addMessages(msgs, out.MetricSetFields)
return out
}
if config.ResolveIDs {
aucoalesce.ResolveIDs(auditEvent)
}
out := mb.Event{
Timestamp: auditEvent.Timestamp,
RootFields: common.MapStr{
"event": common.MapStr{
"category": auditEvent.Category.String(),
"type": strings.ToLower(auditEvent.Type.String()),
"action": auditEvent.Summary.Action,
},
},
ModuleFields: common.MapStr{
"sequence": auditEvent.Sequence,
"result": auditEvent.Result,
"session": auditEvent.Session,
"data": createAuditdData(auditEvent.Data),
},
}
// Add root level fields.
addUser(auditEvent.User, out.RootFields)
addProcess(auditEvent.Process, out.RootFields)
addFile(auditEvent.File, out.RootFields)
addAddress(auditEvent.Source, "source", out.RootFields)
addAddress(auditEvent.Dest, "destination", out.RootFields)
addNetwork(auditEvent.Net, out.RootFields)
if len(auditEvent.Tags) > 0 {
out.RootFields.Put("tags", auditEvent.Tags)
}
// Add module fields.
m := out.ModuleFields
if auditEvent.Summary.Actor.Primary != "" {
m.Put("summary.actor.primary", auditEvent.Summary.Actor.Primary)
}
if auditEvent.Summary.Actor.Secondary != "" {
m.Put("summary.actor.secondary", auditEvent.Summary.Actor.Secondary)
}
if auditEvent.Summary.Object.Primary != "" {
m.Put("summary.object.primary", auditEvent.Summary.Object.Primary)
}
if auditEvent.Summary.Object.Secondary != "" {
m.Put("summary.object.secondary", auditEvent.Summary.Object.Secondary)
}
if auditEvent.Summary.Object.Type != "" {
m.Put("summary.object.type", auditEvent.Summary.Object.Type)
}
if auditEvent.Summary.How != "" {
m.Put("summary.how", auditEvent.Summary.How)
}
if len(auditEvent.Paths) > 0 {
m.Put("paths", auditEvent.Paths)
}
if config.Warnings && len(auditEvent.Warnings) > 0 {
warnings := make([]string, 0, len(auditEvent.Warnings))
for _, err := range auditEvent.Warnings {
warnings = append(warnings, err.Error())
}
m.Put("warnings", warnings)
addMessages(msgs, m)
}
if config.RawMessage {
addMessages(msgs, m)
}
return out
}
func addUser(u aucoalesce.User, m common.MapStr) {
user := make(common.MapStr, len(u.IDs))
m.Put("user", user)
for id, value := range u.IDs {
user[id] = value
if len(u.SELinux) > 0 {
user["selinux"] = u.SELinux
}
if len(u.Names) > 0 {
user["name_map"] = u.Names
}
}
}
func addProcess(p aucoalesce.Process, m common.MapStr) {
if p.IsEmpty() {
return
}
process := common.MapStr{}
m.Put("process", process)
if p.PID != "" {
process["pid"] = p.PID
}
if p.PPID != "" {
process["ppid"] = p.PPID
}
if p.Title != "" {
process["title"] = p.Title
}
if p.Name != "" {
process["name"] = p.Name
}
if p.Exe != "" {
process["exe"] = p.Exe
}
if p.CWD != "" {
process["cwd"] = p.CWD
}
if len(p.Args) > 0 {
process["args"] = p.Args
}
}
func addFile(f *aucoalesce.File, m common.MapStr) {
if f == nil {
return
}
file := common.MapStr{}
m.Put("file", file)
if f.Path != "" {
file["path"] = f.Path
}
if f.Device != "" {
file["device"] = f.Device
}
if f.Inode != "" {
file["inode"] = f.Inode
}
if f.Mode != "" {
file["mode"] = f.Mode
}
if f.UID != "" {
file["uid"] = f.UID
}
if f.GID != "" {
file["gid"] = f.GID
}
if f.Owner != "" {
file["owner"] = f.Owner
}
if f.Group != "" {
file["group"] = f.Group
}
if len(f.SELinux) > 0 {
file["selinux"] = f.SELinux
}
}
func addAddress(addr *aucoalesce.Address, key string, m common.MapStr) {
if addr == nil {
return
}
address := common.MapStr{}
m.Put(key, address)
if addr.Hostname != "" {
address["hostname"] = addr.Hostname
}
if addr.IP != "" {
address["ip"] = addr.IP
}
if addr.Port != "" {
address["port"] = addr.Port
}
if addr.Path != "" {
address["path"] = addr.Path
}
}
func addNetwork(net *aucoalesce.Network, m common.MapStr) {
if net == nil {
return
}
network := common.MapStr{
"direction": net.Direction,
}
m.Put("network", network)
}
func addMessages(msgs []*auparse.AuditMessage, m common.MapStr) {
_, added := m["messages"]
if !added && len(msgs) > 0 {
rawMsgs := make([]string, 0, len(msgs))
for _, msg := range msgs {
rawMsgs = append(rawMsgs, "type="+msg.RecordType.String()+" msg="+msg.RawData)
}
m["messages"] = rawMsgs
}
}
func createAuditdData(data map[string]string) common.MapStr {
out := make(common.MapStr, len(data))
for key, v := range data {
if strings.HasPrefix(key, "socket_") {
out.Put("socket."+key[7:], v)
continue
}
out.Put(key, v)
}
return out
}
// stream type
// stream receives callbacks from the libaudit.Reassembler for completed events
// or lost events that are detected by gaps in sequence numbers.
type stream struct {
done <-chan struct{}
out chan<- []*auparse.AuditMessage
}
func (s *stream) ReassemblyComplete(msgs []*auparse.AuditMessage) {
select {
case <-s.done:
return
case s.out <- msgs:
}
}
func (s *stream) EventsLost(count int) {
lostMetric.Inc()
}
func hasMulticastSupport() bool {
// Check the kernel version because 3.16+ should have multicast
// support.
major, minor, _, err := kernelVersion()
if err != nil {
// Assume not supported.
return false
}
switch {
case major > 3,
major == 3 && minor >= 16:
return true
}
return false
}
func kernelVersion() (major, minor int, full string, err error) {
var uname syscall.Utsname
if err := syscall.Uname(&uname); err != nil {
return 0, 0, "", err
}
length := len(uname.Release)
data := make([]byte, length)
for i, v := range uname.Release {
if v == 0 {
length = i
break
}
data[i] = byte(v)
}
release := string(data[:length])
parts := strings.SplitN(release, ".", 3)
if len(parts) < 2 {
return 0, 0, release, errors.Errorf("failed to parse uname release '%v'", release)
}
major, err = strconv.Atoi(parts[0])
if err != nil {
return 0, 0, release, errors.Wrapf(err, "failed to parse major version from '%v'", release)
}
minor, err = strconv.Atoi(parts[1])
if err != nil {
return 0, 0, release, errors.Wrapf(err, "failed to parse minor version from '%v'", release)
}
return major, minor, release, nil
}
func determineSocketType(c *Config, log *logp.Logger) (string, error) {
client, err := libaudit.NewAuditClient(nil)
if err != nil {
if c.SocketType == "" {
return "", errors.Wrap(err, "failed to create audit client")
}
// Ignore errors if a socket type has been specified. It will fail during
// further setup and its necessary for unit tests to pass
return c.SocketType, nil
}
defer client.Close()
status, err := client.GetStatus()
if err != nil {
if c.SocketType == "" {
return "", errors.Wrap(err, "failed to get audit status")
}
return c.SocketType, nil
}
rules, _ := c.rules()
isLocked := status.Enabled == auditLocked
hasMulticast := hasMulticastSupport()
hasRules := len(rules) > 0
const useAutodetect = "Remove the socket_type option to have auditbeat " +
"select the most suitable subscription method."
switch c.SocketType {
case unicast:
if isLocked {
log.Errorf("requested unicast socket_type is not available "+
"because audit configuration is locked in the kernel "+
"(enabled=2). %s", useAutodetect)
return "", errors.New("unicast socket_type not available")
}
return c.SocketType, nil
case multicast:
if hasMulticast {
if hasRules {
log.Warn("The audit rules specified in the configuration " +
"cannot be applied when using a multicast socket_type.")
}
return c.SocketType, nil
}
log.Errorf("socket_type is set to multicast but based on the "+
"kernel version, multicast audit subscriptions are not supported. %s",
useAutodetect)
return "", errors.New("multicast socket_type not available")
default:
// attempt to determine the optimal socket_type
if hasMulticast {
if hasRules {
if isLocked {
log.Warn("Audit rules specified in the configuration " +
"cannot be applied because the audit rules have been locked " +
"in the kernel (enabled=2). A multicast audit subscription " +
"will be used instead, which does not support setting rules")
return multicast, nil
}
return unicast, nil
}
return multicast, nil
}
if isLocked {
log.Errorf("Cannot continue: audit configuration is locked " +
"in the kernel (enabled=2) which prevents using unicast " +
"sockets. Multicast audit subscriptions are not available " +
"in this kernel. Disable locking the audit configuration " +
"to use auditbeat.")
return "", errors.New("no connection to audit available")
}
return unicast, nil
}
}