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audit_linux.go
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audit_linux.go
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package kernel
import (
"os"
"strconv"
"strings"
"syscall"
"time"
"github.com/pkg/errors"
"github.com/elastic/beats/libbeat/common"
"github.com/elastic/beats/libbeat/common/cfgwarn"
"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 (
metricsetName = "audit.kernel"
logPrefix = "[" + metricsetName + "]"
)
var (
debugf = logp.MakeDebug(metricsetName)
auditMetrics = monitoring.Default.NewRegistry(metricsetName)
lostMetric = monitoring.NewInt(auditMetrics, "lost")
)
func init() {
if err := mb.Registry.AddMetricSet("audit", "kernel", New, parse.EmptyHostParser); err != nil {
panic(err)
}
}
// 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
}
// New constructs a new MetricSet.
func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
cfgwarn.Beta("The %v metricset is a beta feature", metricsetName)
config := defaultConfig
if err := base.Module().UnpackConfig(&config); err != nil {
return nil, errors.Wrap(err, "failed to unpack the audit.kernel config")
}
_, _, kernel, _ := kernelVersion()
debugf("the metricset is running as euid=%v on kernel=%v", os.Geteuid(), kernel)
client, err := newAuditClient(&config)
if err != nil {
return nil, errors.Wrap(err, "failed to create audit.kernel client")
}
lostMetric.Set(0)
return &MetricSet{
BaseMetricSet: base,
client: client,
config: config,
}, nil
}
func newAuditClient(c *Config) (*libaudit.AuditClient, error) {
hasMulticast := hasMulticastSupport()
switch c.SocketType {
// Attempt to determine the optimal socket_type.
case "":
// Use multicast only when no rules are present. Specifying rules
// implies you want control over the audit framework so you should be
// using unicast.
if rules, _ := c.rules(); len(rules) == 0 && hasMulticast {
c.SocketType = "multicast"
logp.Info("%v kernel.socket_type=multicast will be used.", logPrefix)
}
case "multicast":
if !hasMulticast {
logp.Warn("%v kernel.socket_type is set to multicast "+
"but based on the kernel version multicast audit subscriptions "+
"are not supported. unicast will be used instead.", logPrefix)
c.SocketType = "unicast"
}
}
switch c.SocketType {
case "multicast":
return libaudit.NewMulticastAuditClient(nil)
default:
c.SocketType = "unicast"
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.PushReporter) {
defer ms.client.Close()
if err := ms.addRules(reporter); err != nil {
reporter.Error(err)
logp.Err("%v %v", logPrefix, err)
return
}
out, err := ms.receiveEvents(reporter.Done())
if err != nil {
reporter.Error(err)
logp.Err("%v %v", logPrefix, err)
return
}
for {
select {
case <-reporter.Done():
return
case msgs := <-out:
event, err := buildMapStr(msgs, ms.config)
if err != nil {
reporter.ErrorWith(err, event)
} else {
reporter.Event(event)
}
}
}
}
func (ms *MetricSet) addRules(reporter mb.PushReporter) error {
rules, err := ms.config.rules()
if err != nil {
return errors.Wrap(err, "failed to add rules")
}
if len(rules) == 0 {
logp.Info("%v No audit kernel.rules were specified.", logPrefix)
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()
// Delete existing rules.
n, err := client.DeleteRules()
if err != nil {
return errors.Wrap(err, "failed to delete existing rules")
}
logp.Info("%v Deleted %v pre-existing audit rules.", logPrefix, 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 kernel rule '%v'", rule.flags)
reporter.Error(err)
logp.Warn("%v %v", logPrefix, err)
failCount++
}
}
logp.Info("%v Successfully added %d of %d kernel audit rules.",
logPrefix, 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")
}
debugf("audit status from kernel at start: status=%+v", status)
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.SetPID(libaudit.NoWait); err != nil {
return errors.Wrap(err, "failed to set audit 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 {
debugf("dropping message record_type=%v message='%v': ",
raw.Type, string(raw.Data), 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 buildMapStr(msgs []*auparse.AuditMessage, config Config) (common.MapStr, error) {
event, err := aucoalesce.CoalesceMessages(msgs)
if err != nil {
// Add messages on error so that it's possible to debug the problem.
m := common.MapStr{}
addMessages(msgs, m)
return m, err
}
if config.ResolveIDs {
aucoalesce.ResolveIDs(event)
}
m := common.MapStr{
"@timestamp": event.Timestamp,
"sequence": event.Sequence,
"category": event.Category.String(),
"record_type": strings.ToLower(event.Type.String()),
"result": event.Result,
"session": event.Session,
"data": event.Data,
}
if event.Subject.Primary != "" {
m.Put("actor.primary", event.Subject.Primary)
}
if event.Subject.Secondary != "" {
m.Put("actor.secondary", event.Subject.Secondary)
}
if len(event.Subject.Attributes) > 0 {
m.Put("actor.attrs", event.Subject.Attributes)
}
if len(event.Subject.SELinux) > 0 {
m.Put("actor.selinux", event.Subject.SELinux)
}
if event.Object.Primary != "" {
m.Put("thing.primary", event.Object.Primary)
}
if event.Object.Secondary != "" {
m.Put("thing.secondary", event.Object.Secondary)
}
if event.Object.What != "" {
m.Put("thing.what", event.Object.What)
}
if len(event.Object.SELinux) > 0 {
m.Put("thing.selinux", event.Object.SELinux)
}
if event.Action != "" {
m.Put("action", event.Action)
}
if event.How != "" {
m.Put("how", event.How)
}
if event.Key != "" {
m.Put("key", event.Key)
}
if len(event.Paths) > 0 {
m.Put("paths", event.Paths)
}
if len(event.Socket) > 0 {
m.Put("socket", event.Socket)
}
if config.Warnings && len(event.Warnings) > 0 {
warnings := make([]string, 0, len(event.Warnings))
for _, err := range event.Warnings {
warnings = append(warnings, err.Error())
}
m.Put("warnings", warnings)
addMessages(msgs, m)
}
if config.RawMessage {
addMessages(msgs, m)
}
return m, nil
}
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
}
}
// stream type
// stream receives callbacks from the libaudit.Reassmbler 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
}
data := make([]byte, len(uname.Release))
for i, v := range uname.Release {
if v == 0 {
break
}
data[i] = byte(v)
}
release := string(data)
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
}