serving.go

/*
Copyright 2016 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package options

import (
	"context"
	"fmt"
	"net"
	"path"
	"strconv"
	"strings"
	"syscall"

	"github.com/spf13/pflag"
	"k8s.io/klog/v2"
	netutils "k8s.io/utils/net"

	utilnet "k8s.io/apimachinery/pkg/util/net"
	"k8s.io/apiserver/pkg/server"
	"k8s.io/apiserver/pkg/server/dynamiccertificates"
	certutil "k8s.io/client-go/util/cert"
	"k8s.io/client-go/util/keyutil"
	cliflag "k8s.io/component-base/cli/flag"
)

type SecureServingOptions struct {
	BindAddress net.IP
	// BindPort is ignored when Listener is set, will serve https even with 0.
	BindPort int
	// BindNetwork is the type of network to bind to - defaults to "tcp", accepts "tcp",
	// "tcp4", and "tcp6".
	BindNetwork string
	// Required set to true means that BindPort cannot be zero.
	Required bool
	// ExternalAddress is the address advertised, even if BindAddress is a loopback. By default this
	// is set to BindAddress if the later no loopback, or to the first host interface address.
	ExternalAddress net.IP

	// Listener is the secure server network listener.
	// either Listener or BindAddress/BindPort/BindNetwork is set,
	// if Listener is set, use it and omit BindAddress/BindPort/BindNetwork.
	Listener net.Listener

	// ServerCert is the TLS cert info for serving secure traffic
	ServerCert GeneratableKeyCert
	// SNICertKeys are named CertKeys for serving secure traffic with SNI support.
	SNICertKeys []cliflag.NamedCertKey
	// CipherSuites is the list of allowed cipher suites for the server.
	// Values are from tls package constants (https://golang.org/pkg/crypto/tls/#pkg-constants).
	CipherSuites []string
	// MinTLSVersion is the minimum TLS version supported.
	// Values are from tls package constants (https://golang.org/pkg/crypto/tls/#pkg-constants).
	MinTLSVersion string

	// HTTP2MaxStreamsPerConnection is the limit that the api server imposes on each client.
	// A value of zero means to use the default provided by golang's HTTP/2 support.
	HTTP2MaxStreamsPerConnection int

	// PermitPortSharing controls if SO_REUSEPORT is used when binding the port, which allows
	// more than one instance to bind on the same address and port.
	PermitPortSharing bool

	// PermitAddressSharing controls if SO_REUSEADDR is used when binding the port.
	PermitAddressSharing bool
}

type CertKey struct {
	// CertFile is a file containing a PEM-encoded certificate, and possibly the complete certificate chain
	CertFile string
	// KeyFile is a file containing a PEM-encoded private key for the certificate specified by CertFile
	KeyFile string
}

type GeneratableKeyCert struct {
	// CertKey allows setting an explicit cert/key file to use.
	CertKey CertKey

	// CertDirectory specifies a directory to write generated certificates to if CertFile/KeyFile aren't explicitly set.
	// PairName is used to determine the filenames within CertDirectory.
	// If CertDirectory and PairName are not set, an in-memory certificate will be generated.
	CertDirectory string
	// PairName is the name which will be used with CertDirectory to make a cert and key filenames.
	// It becomes CertDirectory/PairName.crt and CertDirectory/PairName.key
	PairName string

	// GeneratedCert holds an in-memory generated certificate if CertFile/KeyFile aren't explicitly set, and CertDirectory/PairName are not set.
	GeneratedCert dynamiccertificates.CertKeyContentProvider

	// FixtureDirectory is a directory that contains test fixture used to avoid regeneration of certs during tests.
	// The format is:
	// <host>_<ip>-<ip>_<alternateDNS>-<alternateDNS>.crt
	// <host>_<ip>-<ip>_<alternateDNS>-<alternateDNS>.key
	FixtureDirectory string
}

func NewSecureServingOptions() *SecureServingOptions {
	return &SecureServingOptions{
		BindAddress: netutils.ParseIPSloppy("0.0.0.0"),
		BindPort:    443,
		ServerCert: GeneratableKeyCert{
			PairName:      "apiserver",
			CertDirectory: "apiserver.local.config/certificates",
		},
	}
}

func (s *SecureServingOptions) DefaultExternalAddress() (net.IP, error) {
	if s.ExternalAddress != nil && !s.ExternalAddress.IsUnspecified() {
		return s.ExternalAddress, nil
	}
	return utilnet.ResolveBindAddress(s.BindAddress)
}

func (s *SecureServingOptions) Validate() []error {
	if s == nil {
		return nil
	}

	errors := []error{}

	if s.Required && s.BindPort < 1 || s.BindPort > 65535 {
		errors = append(errors, fmt.Errorf("--secure-port %v must be between 1 and 65535, inclusive. It cannot be turned off with 0", s.BindPort))
	} else if s.BindPort < 0 || s.BindPort > 65535 {
		errors = append(errors, fmt.Errorf("--secure-port %v must be between 0 and 65535, inclusive. 0 for turning off secure port", s.BindPort))
	}

	if (len(s.ServerCert.CertKey.CertFile) != 0 || len(s.ServerCert.CertKey.KeyFile) != 0) && s.ServerCert.GeneratedCert != nil {
		errors = append(errors, fmt.Errorf("cert/key file and in-memory certificate cannot both be set"))
	}

	return errors
}

func (s *SecureServingOptions) AddFlags(fs *pflag.FlagSet) {
	if s == nil {
		return
	}

	fs.IPVar(&s.BindAddress, "bind-address", s.BindAddress, ""+
		"The IP address on which to listen for the --secure-port port. The "+
		"associated interface(s) must be reachable by the rest of the cluster, and by CLI/web "+
		"clients. If blank or an unspecified address (0.0.0.0 or ::), all interfaces and IP address families will be used.")

	desc := "The port on which to serve HTTPS with authentication and authorization."
	if s.Required {
		desc += " It cannot be switched off with 0."
	} else {
		desc += " If 0, don't serve HTTPS at all."
	}
	fs.IntVar(&s.BindPort, "secure-port", s.BindPort, desc)

	fs.StringVar(&s.ServerCert.CertDirectory, "cert-dir", s.ServerCert.CertDirectory, ""+
		"The directory where the TLS certs are located. "+
		"If --tls-cert-file and --tls-private-key-file are provided, this flag will be ignored.")

	fs.StringVar(&s.ServerCert.CertKey.CertFile, "tls-cert-file", s.ServerCert.CertKey.CertFile, ""+
		"File containing the default x509 Certificate for HTTPS. (CA cert, if any, concatenated "+
		"after server cert). If HTTPS serving is enabled, and --tls-cert-file and "+
		"--tls-private-key-file are not provided, a self-signed certificate and key "+
		"are generated for the public address and saved to the directory specified by --cert-dir.")

	fs.StringVar(&s.ServerCert.CertKey.KeyFile, "tls-private-key-file", s.ServerCert.CertKey.KeyFile,
		"File containing the default x509 private key matching --tls-cert-file.")

	tlsCipherPreferredValues := cliflag.PreferredTLSCipherNames()
	tlsCipherInsecureValues := cliflag.InsecureTLSCipherNames()
	fs.StringSliceVar(&s.CipherSuites, "tls-cipher-suites", s.CipherSuites,
		"Comma-separated list of cipher suites for the server. "+
			"If omitted, the default Go cipher suites will be used. \n"+
			"Preferred values: "+strings.Join(tlsCipherPreferredValues, ", ")+". \n"+
			"Insecure values: "+strings.Join(tlsCipherInsecureValues, ", ")+".")

	tlsPossibleVersions := cliflag.TLSPossibleVersions()
	fs.StringVar(&s.MinTLSVersion, "tls-min-version", s.MinTLSVersion,
		"Minimum TLS version supported. "+
			"Possible values: "+strings.Join(tlsPossibleVersions, ", "))

	fs.Var(cliflag.NewNamedCertKeyArray(&s.SNICertKeys), "tls-sni-cert-key", ""+
		"A pair of x509 certificate and private key file paths, optionally suffixed with a list of "+
		"domain patterns which are fully qualified domain names, possibly with prefixed wildcard "+
		"segments. The domain patterns also allow IP addresses, but IPs should only be used if "+
		"the apiserver has visibility to the IP address requested by a client. "+
		"If no domain patterns are provided, the names of the certificate are "+
		"extracted. Non-wildcard matches trump over wildcard matches, explicit domain patterns "+
		"trump over extracted names. For multiple key/certificate pairs, use the "+
		"--tls-sni-cert-key multiple times. "+
		"Examples: \"example.crt,example.key\" or \"foo.crt,foo.key:*.foo.com,foo.com\".")

	fs.IntVar(&s.HTTP2MaxStreamsPerConnection, "http2-max-streams-per-connection", s.HTTP2MaxStreamsPerConnection, ""+
		"The limit that the server gives to clients for "+
		"the maximum number of streams in an HTTP/2 connection. "+
		"Zero means to use golang's default.")

	fs.BoolVar(&s.PermitPortSharing, "permit-port-sharing", s.PermitPortSharing,
		"If true, SO_REUSEPORT will be used when binding the port, which allows "+
			"more than one instance to bind on the same address and port. [default=false]")

	fs.BoolVar(&s.PermitAddressSharing, "permit-address-sharing", s.PermitAddressSharing,
		"If true, SO_REUSEADDR will be used when binding the port. This allows binding "+
			"to wildcard IPs like 0.0.0.0 and specific IPs in parallel, and it avoids waiting "+
			"for the kernel to release sockets in TIME_WAIT state. [default=false]")
}

// ApplyTo fills up serving information in the server configuration.
func (s *SecureServingOptions) ApplyTo(config **server.SecureServingInfo) error {
	if s == nil {
		return nil
	}
	if s.BindPort <= 0 && s.Listener == nil {
		return nil
	}

	if s.Listener == nil {
		var err error
		addr := net.JoinHostPort(s.BindAddress.String(), strconv.Itoa(s.BindPort))

		c := net.ListenConfig{}

		ctls := multipleControls{}
		if s.PermitPortSharing {
			ctls = append(ctls, permitPortReuse)
		}
		if s.PermitAddressSharing {
			ctls = append(ctls, permitAddressReuse)
		}
		if len(ctls) > 0 {
			c.Control = ctls.Control
		}

		s.Listener, s.BindPort, err = CreateListener(s.BindNetwork, addr, c)
		if err != nil {
			return fmt.Errorf("failed to create listener: %v", err)
		}
	} else {
		if _, ok := s.Listener.Addr().(*net.TCPAddr); !ok {
			return fmt.Errorf("failed to parse ip and port from listener")
		}
		s.BindPort = s.Listener.Addr().(*net.TCPAddr).Port
		s.BindAddress = s.Listener.Addr().(*net.TCPAddr).IP
	}

	*config = &server.SecureServingInfo{
		Listener:                     s.Listener,
		HTTP2MaxStreamsPerConnection: s.HTTP2MaxStreamsPerConnection,
	}
	c := *config

	serverCertFile, serverKeyFile := s.ServerCert.CertKey.CertFile, s.ServerCert.CertKey.KeyFile
	// load main cert *original description until 2023-08-18*

	/*
		kubernetes mutual (2-way) x509 between client and apiserver:

			>1. apiserver sending its apiserver certificate along with its publickey to client
			2. client verifies the apiserver certificate sent against its cluster certificate authority data
			3. client sending its client certificate along with its public key to the apiserver
			4. apiserver verifies the client certificate sent against its cluster certificate authority data

			description:
				here, with this block,
				apiserver certificate and pub key data (along with priv key)get loaded into server.SecureServingInfo
				for client to later in the step 2 verify the apiserver certificate during the handshake
				when making a request

			normal args related to this stage:
				--tls-cert-file string  File containing the default x509 Certificate for HTTPS.
					(CA cert, if any, concatenated after server cert). If HTTPS serving is enabled, and
					--tls-cert-file and --tls-private-key-file are not provided, a self-signed certificate
					and key are generated for the public address and saved to the directory specified by
					--cert-dir
				--tls-private-key-file string  File containing the default x509 private key matching --tls-cert-file.

				(retrievable from "kube-apiserver --help" command)
				(suggested by @deads2k)

			see also:
				- for the step 2, see: staging/src/k8s.io/client-go/transport/transport.go
				- for the step 3, see: staging/src/k8s.io/client-go/transport/transport.go
				- for the step 4, see: staging/src/k8s.io/apiserver/pkg/authentication/request/x509/x509.go
	*/

	if len(serverCertFile) != 0 || len(serverKeyFile) != 0 {
		var err error
		c.Cert, err = dynamiccertificates.NewDynamicServingContentFromFiles("serving-cert", serverCertFile, serverKeyFile)
		if err != nil {
			return err
		}
	} else if s.ServerCert.GeneratedCert != nil {
		c.Cert = s.ServerCert.GeneratedCert
	}

	if len(s.CipherSuites) != 0 {
		cipherSuites, err := cliflag.TLSCipherSuites(s.CipherSuites)
		if err != nil {
			return err
		}
		c.CipherSuites = cipherSuites
	}

	var err error
	c.MinTLSVersion, err = cliflag.TLSVersion(s.MinTLSVersion)
	if err != nil {
		return err
	}

	// load SNI certs
	namedTLSCerts := make([]dynamiccertificates.SNICertKeyContentProvider, 0, len(s.SNICertKeys))
	for _, nck := range s.SNICertKeys {
		tlsCert, err := dynamiccertificates.NewDynamicSNIContentFromFiles("sni-serving-cert", nck.CertFile, nck.KeyFile, nck.Names...)
		namedTLSCerts = append(namedTLSCerts, tlsCert)
		if err != nil {
			return fmt.Errorf("failed to load SNI cert and key: %v", err)
		}
	}
	c.SNICerts = namedTLSCerts

	return nil
}

func (s *SecureServingOptions) MaybeDefaultWithSelfSignedCerts(publicAddress string, alternateDNS []string, alternateIPs []net.IP) error {
	if s == nil || (s.BindPort == 0 && s.Listener == nil) {
		return nil
	}
	keyCert := &s.ServerCert.CertKey
	if len(keyCert.CertFile) != 0 || len(keyCert.KeyFile) != 0 {
		return nil
	}

	canReadCertAndKey := false
	if len(s.ServerCert.CertDirectory) > 0 {
		if len(s.ServerCert.PairName) == 0 {
			return fmt.Errorf("PairName is required if CertDirectory is set")
		}
		keyCert.CertFile = path.Join(s.ServerCert.CertDirectory, s.ServerCert.PairName+".crt")
		keyCert.KeyFile = path.Join(s.ServerCert.CertDirectory, s.ServerCert.PairName+".key")
		if canRead, err := certutil.CanReadCertAndKey(keyCert.CertFile, keyCert.KeyFile); err != nil {
			return err
		} else {
			canReadCertAndKey = canRead
		}
	}

	if !canReadCertAndKey {
		// add either the bind address or localhost to the valid alternates
		if s.BindAddress.IsUnspecified() {
			alternateDNS = append(alternateDNS, "localhost")
		} else {
			alternateIPs = append(alternateIPs, s.BindAddress)
		}

		if cert, key, err := certutil.GenerateSelfSignedCertKeyWithFixtures(publicAddress, alternateIPs, alternateDNS, s.ServerCert.FixtureDirectory); err != nil {
			return fmt.Errorf("unable to generate self signed cert: %v", err)
		} else if len(keyCert.CertFile) > 0 && len(keyCert.KeyFile) > 0 {
			if err := certutil.WriteCert(keyCert.CertFile, cert); err != nil {
				return err
			}
			if err := keyutil.WriteKey(keyCert.KeyFile, key); err != nil {
				return err
			}
			klog.Infof("Generated self-signed cert (%s, %s)", keyCert.CertFile, keyCert.KeyFile)
		} else {
			s.ServerCert.GeneratedCert, err = dynamiccertificates.NewStaticCertKeyContent("Generated self signed cert", cert, key)
			if err != nil {
				return err
			}
			klog.Infof("Generated self-signed cert in-memory")
		}
	}

	return nil
}

func CreateListener(network, addr string, config net.ListenConfig) (net.Listener, int, error) {
	if len(network) == 0 {
		network = "tcp"
	}

	ln, err := config.Listen(context.TODO(), network, addr)
	if err != nil {
		return nil, 0, fmt.Errorf("failed to listen on %v: %v", addr, err)
	}

	// get port
	tcpAddr, ok := ln.Addr().(*net.TCPAddr)
	if !ok {
		ln.Close()
		return nil, 0, fmt.Errorf("invalid listen address: %q", ln.Addr().String())
	}

	return ln, tcpAddr.Port, nil
}

type multipleControls []func(network, addr string, conn syscall.RawConn) error

func (mcs multipleControls) Control(network, addr string, conn syscall.RawConn) error {
	for _, c := range mcs {
		if err := c(network, addr, conn); err != nil {
			return err
		}
	}
	return nil
}