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package api
import (
"context"
"crypto/tls"
"crypto/x509"
"encoding/json"
"errors"
"fmt"
"net"
"net/http"
"sync/atomic"
"github.com/julienschmidt/httprouter"
"github.com/linkerd/linkerd2/controller/k8s"
pkgk8s "github.com/linkerd/linkerd2/pkg/k8s"
"github.com/linkerd/linkerd2/pkg/prometheus"
pkgTls "github.com/linkerd/linkerd2/pkg/tls"
pb "github.com/linkerd/linkerd2/viz/tap/gen/tap"
"github.com/sirupsen/logrus"
log "github.com/sirupsen/logrus"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)
// Server holds the underlying http server and its config
type Server struct {
*http.Server
listener net.Listener
router *httprouter.Router
allowedNames []string
certValue *atomic.Value
log *logrus.Entry
}
// NewServer creates a new server that implements the Tap APIService.
func NewServer(
ctx context.Context,
addr string,
k8sAPI *k8s.API,
grpcTapServer pb.TapServer,
disableCommonNames bool,
) (*Server, error) {
updateEvent := make(chan struct{})
errEvent := make(chan error)
watcher := pkgTls.NewFsCredsWatcher(pkgk8s.MountPathTLSBase, updateEvent, errEvent).
WithFilePaths(pkgk8s.MountPathTLSCrtPEM, pkgk8s.MountPathTLSKeyPEM)
go func() {
if err := watcher.StartWatching(ctx); err != nil {
log.Fatalf("Failed to start creds watcher: %s", err)
}
}()
clientCAPem, allowedNames, usernameHeader, groupHeader, err := serverAuth(ctx, k8sAPI)
if err != nil {
return nil, err
}
// for development
if disableCommonNames {
allowedNames = []string{}
}
log := logrus.WithFields(logrus.Fields{
"component": "tap",
"addr": addr,
})
clientCertPool := x509.NewCertPool()
clientCertPool.AppendCertsFromPEM([]byte(clientCAPem))
httpServer := &http.Server{
Addr: addr,
TLSConfig: &tls.Config{
ClientAuth: tls.VerifyClientCertIfGiven,
ClientCAs: clientCertPool,
MinVersion: tls.VersionTLS12,
},
}
var emptyCert atomic.Value
h := &handler{
k8sAPI: k8sAPI,
usernameHeader: usernameHeader,
groupHeader: groupHeader,
grpcTapServer: grpcTapServer,
log: log,
}
lis, err := net.Listen("tcp", addr)
if err != nil {
return nil, fmt.Errorf("net.Listen failed with: %w", err)
}
s := &Server{
Server: httpServer,
listener: lis,
router: initRouter(h),
allowedNames: allowedNames,
certValue: &emptyCert,
log: log,
}
s.Handler = prometheus.WithTelemetry(s)
httpServer.TLSConfig.GetCertificate = s.getCertificate
if err := watcher.UpdateCert(s.certValue); err != nil {
return nil, fmt.Errorf("failed to initialized certificate: %w", err)
}
go watcher.ProcessEvents(log, s.certValue, updateEvent, errEvent)
return s, nil
}
// Start starts the https server
func (a *Server) Start(ctx context.Context) {
a.log.Infof("starting tap API server on %s", a.Server.Addr)
if err := a.ServeTLS(a.listener, "", ""); err != nil {
if errors.Is(err, http.ErrServerClosed) {
return
}
a.log.Fatal(err)
}
}
func (a *Server) getCertificate(_ *tls.ClientHelloInfo) (*tls.Certificate, error) {
return a.certValue.Load().(*tls.Certificate), nil
}
// ServeHTTP handles all routes for the Server.
func (a *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
a.log.Debugf("ServeHTTP(): %+v", req)
if err := a.validate(req); err != nil {
a.log.Debug(err)
renderJSONError(w, err, http.StatusBadRequest)
} else {
a.router.ServeHTTP(w, req)
}
}
// validate ensures that the request should be honored returning an error otherwise.
func (a *Server) validate(req *http.Request) error {
// if `requestheader-allowed-names` was empty, allow any CN
if len(a.allowedNames) > 0 {
for _, cn := range a.allowedNames {
for _, clientCert := range req.TLS.PeerCertificates {
// Check Common Name and Subject Alternate Name(s)
if cn == clientCert.Subject.CommonName || isSubjectAlternateName(clientCert, cn) {
return nil
}
}
}
// Build the set of certificate names for the error message
clientNames := []string{}
for _, clientCert := range req.TLS.PeerCertificates {
clientNames = append(clientNames, clientCert.Subject.CommonName)
}
return fmt.Errorf("no valid CN found. allowed names: %s, client names: %s", a.allowedNames, clientNames)
}
return nil
}
// serverAuth parses the relevant data out of a ConfigMap to enable client TLS
// authentication.
// kubectl -n kube-system get cm/extension-apiserver-authentication
// accessible via the extension-apiserver-authentication-reader role
func serverAuth(ctx context.Context, k8sAPI *k8s.API) (string, []string, string, string, error) {
cm, err := k8sAPI.Client.CoreV1().
ConfigMaps(metav1.NamespaceSystem).
Get(ctx, pkgk8s.ExtensionAPIServerAuthenticationConfigMapName, metav1.GetOptions{})
if err != nil {
return "", nil, "", "", fmt.Errorf("failed to load [%s] config: %w", pkgk8s.ExtensionAPIServerAuthenticationConfigMapName, err)
}
clientCAPem, ok := cm.Data[pkgk8s.ExtensionAPIServerAuthenticationRequestHeaderClientCAFileKey]
if !ok {
return "", nil, "", "", fmt.Errorf("no client CA cert available for apiextension-server")
}
allowedNames, err := deserializeStrings(cm.Data["requestheader-allowed-names"])
if err != nil {
return "", nil, "", "", err
}
usernameHeaders, err := deserializeStrings(cm.Data["requestheader-username-headers"])
if err != nil {
return "", nil, "", "", err
}
usernameHeader := ""
if len(usernameHeaders) > 0 {
usernameHeader = usernameHeaders[0]
}
groupHeaders, err := deserializeStrings(cm.Data["requestheader-group-headers"])
if err != nil {
return "", nil, "", "", err
}
groupHeader := ""
if len(groupHeaders) > 0 {
groupHeader = groupHeaders[0]
}
return clientCAPem, allowedNames, usernameHeader, groupHeader, nil
}
// copied from https://github.com/kubernetes/apiserver/blob/781c3cd1b3dc5b6f79c68ab0d16fe544600421ef/pkg/server/options/authentication.go#L360
func deserializeStrings(in string) ([]string, error) {
if in == "" {
return nil, nil
}
var ret []string
if err := json.Unmarshal([]byte(in), &ret); err != nil {
return nil, err
}
return ret, nil
}
// isSubjectAlternateName checks all applicable fields within the certificate for a match to the provided name.
// See https://tools.ietf.org/html/rfc5280#section-4.2.1.6 for information about Subject Alternate Name.
func isSubjectAlternateName(cert *x509.Certificate, name string) bool {
for _, dnsName := range cert.DNSNames {
if dnsName == name {
return true
}
}
for _, emailAddress := range cert.EmailAddresses {
if emailAddress == name {
return true
}
}
for _, ip := range cert.IPAddresses {
if ip.String() == name {
return true
}
}
for _, url := range cert.URIs {
if url.String() == name {
return true
}
}
return false
}