crypto/tls: should apply default NextProtos to the result of GetConfigForClient

[xinst]

Go version

go version go1.22.8 darwin/amd64

Output of go env in your module/workspace:

GO111MODULE='on'
GOARCH='arm64'
GOBIN='/Users/jack/src/bin'
GOCACHE='/Users/jack/Library/Caches/go-build'
GOENV='/Users/jack/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOMODCACHE='/Users/jack/src/pkg/mod'
GOOS='darwin'
GOPATH='/Users/jack/src'
GOPROXY='https://goproxy.cn,direct'
GOROOT='/Users/jack/go/go1.22.8'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/jack/go/go1.22.8/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.8'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'

What did you do?

I start a service with multiple domains, use GetConfigForClient function for providing TLS certificates dynamically depends on the request's servername. Start go1.6 has enable http2 by default, and it will add supported application level protocols,such as "h2","http/1.1", but the tls.Config from GetConfigForClient did not do this.

// readClientHello reads a ClientHello message and selects the protocol version.
func (c *Conn) readClientHello(ctx context.Context) (*clientHelloMsg, error) {
	// clientHelloMsg is included in the transcript, but we haven't initialized
	// it yet. The respective handshake functions will record it themselves.
	msg, err := c.readHandshake(nil)
	if err != nil {
		return nil, err
	}
	clientHello, ok := msg.(*clientHelloMsg)
	if !ok {
		c.sendAlert(alertUnexpectedMessage)
		return nil, unexpectedMessageError(clientHello, msg)
	}

	var configForClient *Config
	originalConfig := c.config
	if c.config.**GetConfigForClient** != nil {
		chi := clientHelloInfo(ctx, c, clientHello)
		if configForClient, err = c.config.**GetConfigForClient**(chi); err != nil {
			c.sendAlert(alertInternalError)
			return nil, err
		} else if configForClient != nil {
			c.config = configForClient
		}
	}

this leads to the client request offers h2,http/1.1, but server only accepted http/1.1 only

What did you see happen?

 IPv4: xx.xx.xxx.xx
*   Trying xx.xx.xxx.xx:443...
* ALPN: curl offers h2,http/1.1
} [5 bytes data]
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
} [512 bytes data]
*  CAfile: ca.pem
*  CApath: none
{ [5 bytes data]
* TLSv1.3 (IN), TLS handshake, Server hello (2):
{ [122 bytes data]
* TLSv1.3 (IN), TLS change cipher, Change cipher spec (1):
{ [1 bytes data]
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
{ [25 bytes data]
* TLSv1.3 (IN), TLS handshake, Request CERT (13):
{ [229 bytes data]
* TLSv1.3 (IN), TLS handshake, Certificate (11):
{ [1035 bytes data]
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
{ [264 bytes data]
* TLSv1.3 (IN), TLS handshake, Finished (20):
{ [52 bytes data]
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
} [1 bytes data]
* TLSv1.3 (OUT), TLS handshake, Certificate (11):
} [2087 bytes data]
* TLSv1.3 (OUT), TLS handshake, CERT verify (15):
} [264 bytes data]
* TLSv1.3 (OUT), TLS handshake, Finished (20):
} [52 bytes data]
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 / x25519 / RSASSA-PSS
* ALPN: server accepted http/1.1

What did you expect to see?

if the NextProtos of tls.Config is empty, should copy from originalConfig, It should be consistent with the default

[gabyhelp]

Related Issues and Documentation

• crypto/tls: cannot enforce "h2" with ALPN #59734
• x/net/http2: `http.Server.Serve` doesn't serve http2 traffic #14374 (closed)
• net/http: ConfigureTransport does not work for Transport with custom DialTLS #41236
• net/http: Request.URL contains only path value when requested via http2 #68365 (closed)
• net/http/httptest: NewTLSServer doesn't support HTTP/2 requests #34939 (closed)
• x/net/http2: call conn.Handshake before accessing ConnectionState #33304
• crypto/tls: Can't create a request using just one cipher suite with TLS v1.3 #68854 (closed)
• net/http/httptest: Server does not check GetCertificate #63812
• crypto/tls: RequireAndVerifyClientCert is not working as intended. #63122 (closed)
• net/http: h2 does not support other net.Conn than *tls.Conn #55076

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

Please show a reproducer.
The following code gets me HTTP2:

package main

import (
	"crypto/tls"
	"fmt"
	"net/http"
)

func main() {
	crt, err := tls.LoadX509KeyPair("localhost.pem", "localhost-key.pem")
	if err != nil {
		panic(err)
	}

	svr := &http.Server{
		Addr: ":8443",
		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			fmt.Fprintln(w, "hello world")
		}),
		TLSConfig: &tls.Config{
			GetCertificate: func(chi *tls.ClientHelloInfo) (*tls.Certificate, error) {
				return &crt, nil
			},
		},
	}
	panic(svr.ListenAndServeTLS("", ""))
}

curl:

$ curl -v https://localhost:8443/hello
* Couldn't find host localhost in the .netrc file; using defaults
* Host localhost:8443 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:8443...
* ALPN: curl offers h2,http/1.1
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
*  CAfile: /etc/ssl/certs/ca-certificates.crt
*  CApath: none
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.3 (IN), TLS change cipher, Change cipher spec (1):
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
* TLSv1.3 (IN), TLS handshake, Certificate (11):
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
* TLSv1.3 (IN), TLS handshake, Finished (20):
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.3 (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / TLS_AES_128_GCM_SHA256 / x25519 / RSASSA-PSS
* ALPN: server accepted h2
* Server certificate:
*  subject: O=mkcert development certificate; OU=user@hwaryun
*  start date: Nov  6 17:36:49 2024 GMT
*  expire date: Feb  6 17:36:49 2027 GMT
*  subjectAltName: host "localhost" matched cert's "localhost"
*  issuer: O=mkcert development CA; OU=user@hwaryun; CN=mkcert user@hwaryun
*  SSL certificate verify ok.
*   Certificate level 0: Public key type RSA (2048/112 Bits/secBits), signed using sha256WithRSAEncryption
*   Certificate level 1: Public key type RSA (3072/128 Bits/secBits), signed using sha256WithRSAEncryption
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* Connected to localhost (::1) port 8443
* using HTTP/2
* [HTTP/2] [1] OPENED stream for https://localhost:8443/hello
* [HTTP/2] [1] [:method: GET]
* [HTTP/2] [1] [:scheme: https]
* [HTTP/2] [1] [:authority: localhost:8443]
* [HTTP/2] [1] [:path: /hello]
* [HTTP/2] [1] [user-agent: curl/8.10.1]
* [HTTP/2] [1] [accept: */*]
> GET /hello HTTP/2
> Host: localhost:8443
> User-Agent: curl/8.10.1
> Accept: */*
> 
* Request completely sent off
< HTTP/2 200 
< content-type: text/plain; charset=utf-8
< content-length: 12
< date: Wed, 06 Nov 2024 17:41:15 GMT
< 
hello world
* Connection #0 to host localhost left intact

[xinst]

sorry for misleading, the callback function is GetConfigForClient

package main

import (
	"crypto/tls"
	"fmt"
	"net/http"
)


var gTlsCfg = &tls.Config{
		ClientAuth:               tls.RequireAndVerifyClientCert,
		Certificates:             tlsCertArr,
		RootCAs:                  pool,
		ClientCAs:                pool,
		InsecureSkipVerify:       false,
		MinVersion:               tls.VersionTLS12,
	}

func getTlsConfigForClient(chi *tls.ClientHelloInfo) (*tls.Config, error) {	
	if chi.ServerName == "example.com" {	
		tlsCfg := &tls.Config{
			ClientAuth:               tls.RequireAndVerifyClientCert,
			Certificates:             tlsCertArr,
			RootCAs:                  pool,
			ClientCAs:                pool,
			InsecureSkipVerify:       false,
			MinVersion:               tls.VersionTLS13,
		}
		return tlsCfg, nil
	}
	return gTlsCfg
}

func main() {
	svr := &http.Server{
		Addr: ":8443",
		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			fmt.Fprintln(w, "hello world")
		}),
		TLSConfig: gTlsCfg,
	}
	svr.TLSConfig.GetConfigForClient = getTlsConfigForClient
	panic(svr.ListenAndServeTLS("", ""))
}

[seankhliao]

cc @golang/security