feature: Hijack HTTPS by generating leaf TLS certs on the fly issued by user provided CA.

dfdaemon/proxy/cert.go

@@ -0,0 +1,78 @@
+/*
+ * Copyright The Dragonfly 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 proxy
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"errors"
+	"math/big"
+	"net"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+type LeafCertSpec struct {
+	publicKey crypto.PublicKey
+
+	privateKey crypto.PrivateKey
+
+	signatureAlgorithm x509.SignatureAlgorithm
+}
+
+// genLeafCert generates a Leaf TLS certificate and sign it with given CA
+func genLeafCert(ca *tls.Certificate, leafCertSpec *LeafCertSpec, host string) (*tls.Certificate, error) {
+	now := time.Now().Add(-1 * time.Hour).UTC()
+	if !ca.Leaf.IsCA {
+		return nil, errors.New("CA cert is not a CA")
+	}
+	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
+	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
+	if err != nil {
+		logrus.Errorf("failed to generate serial number: %s", err)
+		return nil, err
+	}
+	tmpl := &x509.Certificate{
+		SerialNumber:          serialNumber,
+		Subject:               pkix.Name{CommonName: host},
+		NotBefore:             now,
+		NotAfter:              now.Add(24 * time.Hour),
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageDataEncipherment | x509.KeyUsageKeyAgreement,
+		BasicConstraintsValid: true,
+		SignatureAlgorithm:    leafCertSpec.signatureAlgorithm,
+	}
+	ip := net.ParseIP(host)
+	if ip == nil {
+		tmpl.DNSNames = []string{host}
+	} else {
+		tmpl.IPAddresses = []net.IP{ip}
+	}
+	newCert, err := x509.CreateCertificate(rand.Reader, tmpl, ca.Leaf, leafCertSpec.publicKey, ca.PrivateKey)
+	if err != nil {
+		logrus.Errorf("failed to generate leaf cert %s", err)
+		return nil, err
+	}
+	cert := new(tls.Certificate)
+	cert.Certificate = append(cert.Certificate, newCert)
+	cert.PrivateKey = leafCertSpec.privateKey
+	cert.Leaf, _ = x509.ParseCertificate(newCert)
+	return cert, nil
+}

dfdaemon/proxy/proxy.go

@@ -18,6 +18,7 @@ package proxy
 
 import (
 	"crypto/tls"
+	"crypto/x509"
 	"fmt"
 	"io"
 	"net"
@@ -31,7 +32,7 @@ import (
 	"github.com/dragonflyoss/Dragonfly/dfdaemon/downloader"
 	"github.com/dragonflyoss/Dragonfly/dfdaemon/downloader/dfget"
 	"github.com/dragonflyoss/Dragonfly/dfdaemon/transport"
-
+	"github.com/golang/groupcache/lru"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -72,6 +73,11 @@ func WithCertFromFile(certFile, keyFile string) Option {
 			return errors.Wrap(err, "load cert")
 		}
 		logrus.Infof("use self-signed certificate (%s, %s) for https hijacking", certFile, keyFile)
+		leaf, err := x509.ParseCertificate(cert.Certificate[0])
+		if err != nil {
+			return errors.Wrap(err, "load leaf cert")
+		}
+		cert.Leaf = leaf
 		p.cert = &cert
 		return nil
 	}
@@ -168,6 +174,8 @@ type Proxy struct {
 	httpsHosts []*config.HijackHost
 	// cert is the certificate used to hijack https proxy requests
 	cert *tls.Certificate
+	// certCache is a in-memory cache store for TLS certs used in HTTPS hijack. Lazy init.
+	certCache *lru.Cache
 	// directHandler are used to handle non proxy requests
 	directHandler http.Handler
 	// downloadFactory returns the downloader used for p2p downloading
@@ -314,7 +322,38 @@ func (proxy *Proxy) handleHTTPS(w http.ResponseWriter, r *http.Request) {
 	logrus.Debugln("hijack https request to", r.Host)
 
 	sConfig := new(tls.Config)
-	sConfig.Certificates = []tls.Certificate{*proxy.cert}
+	if proxy.cert.Leaf != nil && proxy.cert.Leaf.IsCA {
+		if proxy.certCache == nil { // Initialize proxy.certCache on first access. (Lazy init)
+			proxy.certCache = lru.New(100) // Default max entries size = 100
+		}
+		logrus.Debugf("hijack https request with CA <%s>", proxy.cert.Leaf.Subject.CommonName)
+		leafCertSpec := LeafCertSpec{
+			proxy.cert.Leaf.PublicKey,
+			proxy.cert.PrivateKey,
+			proxy.cert.Leaf.SignatureAlgorithm}
+		host, _, _ := net.SplitHostPort(r.Host)
+		sConfig.GetCertificate = func(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
+			cConfig.ServerName = host
+			logrus.Debugf("Generate temporal leaf TLS cert for ServerName <%s>, host <%s>", hello.ServerName, host)
+			// It's assumed that `hello.ServerName` is always same as `host`, in practice.
+			cacheKey := host
+			cached, hit := proxy.certCache.Get(cacheKey)
+			if hit && time.Now().Before(cached.(*tls.Certificate).Leaf.NotAfter) { // If cache hit and the cert is not expired
+				logrus.Debugf("TLS Cache hit, cacheKey = <%s>", cacheKey)
+				return cached.(*tls.Certificate), nil
+			}
+			cert, err := genLeafCert(proxy.cert, &leafCertSpec, host)
+			if err == nil {
+				// Put cert in cache only if there is no error. So all certs in cache are always valid.
+				// But certs in cache maybe expired (After 24 hours, see the default duration of generated certs)
+				proxy.certCache.Add(cacheKey, cert)
+			}
+			// If err != nil, means unrecoverable error happened in genLeafCert(...)
+			return cert, err
+		}
+	} else {
+		sConfig.Certificates = []tls.Certificate{*proxy.cert}
+	}
 
 	sConn, err := handshake(w, sConfig)
 	if err != nil {

go.mod

@@ -19,6 +19,7 @@ require (
 	github.com/go-openapi/strfmt v0.0.0-20171222154016-4dd3d302e100
 	github.com/go-openapi/swag v0.0.0-20170606142751-f3f9494671f9
 	github.com/go-openapi/validate v0.0.0-20170705144413-8a82927c942c
+	github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef
 	github.com/golang/mock v1.3.1
 	github.com/gorilla/context v0.0.0-20181012153548-51ce91d2eadd // indirect
 	github.com/gorilla/mux v1.5.0

go.sum

@@ -63,6 +63,7 @@ github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/me
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef h1:veQD95Isof8w9/WXiA+pa3tz3fJXkt5B7QaRBrM62gk=
 github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/mock v1.1.1 h1:G5FRp8JnTd7RQH5kemVNlMeyXQAztQ3mOWV95KxsXH8=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=