fix(ssh): unable to pass a custom HostKeyCallback func

Don't overwrite HostKeyCallback if one is provided.

Fixes: c35b808 ("plumbing: transport/ssh, auto-populate ClientConfig.HostKeyAlgorithms. Fixes go-git#411")
Fixes: go-git#654
Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>

plumbing/transport/ssh/auth_method.go

@@ -43,6 +43,7 @@ const (
 type KeyboardInteractive struct {
 	User      string
 	Challenge ssh.KeyboardInteractiveChallenge
+	HostKeyCallbackHelper
 }
 
 func (a *KeyboardInteractive) Name() string {
@@ -54,18 +55,19 @@ func (a *KeyboardInteractive) String() string {
 }
 
 func (a *KeyboardInteractive) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{
 			a.Challenge,
 		},
-	}, nil
+	})
 }
 
 // Password implements AuthMethod by using the given password.
 type Password struct {
 	User     string
 	Password string
+	HostKeyCallbackHelper
 }
 
 func (a *Password) Name() string {
@@ -77,17 +79,18 @@ func (a *Password) String() string {
 }
 
 func (a *Password) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.Password(a.Password)},
-	}, nil
+	})
 }
 
 // PasswordCallback implements AuthMethod by using a callback
 // to fetch the password.
 type PasswordCallback struct {
 	User     string
 	Callback func() (pass string, err error)
+	HostKeyCallbackHelper
 }
 
 func (a *PasswordCallback) Name() string {
@@ -99,16 +102,17 @@ func (a *PasswordCallback) String() string {
 }
 
 func (a *PasswordCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
-	}, nil
+	})
 }
 
 // PublicKeys implements AuthMethod by using the given key pairs.
 type PublicKeys struct {
 	User   string
 	Signer ssh.Signer
+	HostKeyCallbackHelper
 }
 
 // NewPublicKeys returns a PublicKeys from a PEM encoded private key. An
@@ -147,10 +151,10 @@ func (a *PublicKeys) String() string {
 }
 
 func (a *PublicKeys) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
-	}, nil
+	})
 }
 
 func username() (string, error) {
@@ -173,6 +177,7 @@ func username() (string, error) {
 type PublicKeysCallback struct {
 	User     string
 	Callback func() (signers []ssh.Signer, err error)
+	HostKeyCallbackHelper
 }
 
 // NewSSHAgentAuth returns a PublicKeysCallback based on a SSH agent, it opens
@@ -207,10 +212,10 @@ func (a *PublicKeysCallback) String() string {
 }
 
 func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
-	}, nil
+	})
 }
 
 // NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a
@@ -286,9 +291,6 @@ func filterKnownHostsFiles(files ...string) ([]string, error) {
 
 // HostKeyCallbackHelper is a helper that provides common functionality to
 // configure HostKeyCallback into a ssh.ClientConfig.
-// Deprecated in favor of SetConfigHostKeyFields (see common.go) which provides
-// a mechanism for also setting ClientConfig.HostKeyAlgorithms for a specific
-// host.
 type HostKeyCallbackHelper struct {
 	// HostKeyCallback is the function type used for verifying server keys.
 	// If nil default callback will be create using NewKnownHostsCallback

plumbing/transport/ssh/common.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/go-git/go-git/v5/plumbing/transport"
 	"github.com/go-git/go-git/v5/plumbing/transport/internal/common"
+	"github.com/skeema/knownhosts"
 
 	"github.com/kevinburke/ssh_config"
 	"golang.org/x/crypto/ssh"
@@ -122,9 +123,18 @@ func (c *command) connect() error {
 		return err
 	}
 	hostWithPort := c.getHostWithPort()
-	config, err = SetConfigHostKeyFields(config, hostWithPort)
-	if err != nil {
-		return err
+	if config.HostKeyCallback == nil {
+		kh, err := newKnownHosts()
+		if err != nil {
+			return err
+		}
+		config.HostKeyCallback = kh.HostKeyCallback()
+		config.HostKeyAlgorithms = kh.HostKeyAlgorithms(hostWithPort)
+	} else if len(config.HostKeyAlgorithms) == 0 {
+		// Set the HostKeyAlgorithms based on HostKeyCallback.
+		// For background see https://github.com/go-git/go-git/issues/411 as well as
+		// https://github.com/golang/go/issues/29286 for root cause.
+		config.HostKeyAlgorithms = knownhosts.HostKeyAlgorithms(config.HostKeyCallback, hostWithPort)
 	}
 
 	overrideConfig(c.config, config)
@@ -167,23 +177,6 @@ func dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
 	return ssh.NewClient(c, chans, reqs), nil
 }
 
-// SetConfigHostKeyFields sets cfg.HostKeyCallback and cfg.HostKeyAlgorithms
-// based on OpenSSH known_hosts. cfg is modified in-place. hostWithPort must be
-// supplied, since the algorithms will be set based on the known host keys for
-// that specific host. Otherwise, golang.org/x/crypto/ssh can return an error
-// upon connecting to a host whose *first* key is not known, even though other
-// keys (of different types) are known and match properly.
-// For background see https://github.com/go-git/go-git/issues/411 as well as
-// https://github.com/golang/go/issues/29286 for root cause.
-func SetConfigHostKeyFields(cfg *ssh.ClientConfig, hostWithPort string) (*ssh.ClientConfig, error) {
-	kh, err := newKnownHosts()
-	if err == nil {
-		cfg.HostKeyCallback = kh.HostKeyCallback()
-		cfg.HostKeyAlgorithms = kh.HostKeyAlgorithms(hostWithPort)
-	}
-	return cfg, err
-}
-
 func (c *command) getHostWithPort() string {
 	if addr, found := c.doGetHostWithPortFromSSHConfig(); found {
 		return addr

plumbing/transport/ssh/common_test.go

@@ -5,23 +5,25 @@ import (
 
 	"github.com/go-git/go-git/v5/plumbing/transport"
 
+	"github.com/gliderlabs/ssh"
 	"github.com/kevinburke/ssh_config"
-	"golang.org/x/crypto/ssh"
+	stdssh "golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/testdata"
 	. "gopkg.in/check.v1"
 )
 
 func Test(t *testing.T) { TestingT(t) }
 
 func (s *SuiteCommon) TestOverrideConfig(c *C) {
-	config := &ssh.ClientConfig{
+	config := &stdssh.ClientConfig{
 		User: "foo",
-		Auth: []ssh.AuthMethod{
-			ssh.Password("yourpassword"),
+		Auth: []stdssh.AuthMethod{
+			stdssh.Password("yourpassword"),
 		},
-		HostKeyCallback: ssh.FixedHostKey(nil),
+		HostKeyCallback: stdssh.FixedHostKey(nil),
 	}
 
-	target := &ssh.ClientConfig{}
+	target := &stdssh.ClientConfig{}
 	overrideConfig(config, target)
 
 	c.Assert(target.User, Equals, "foo")
@@ -30,11 +32,11 @@ func (s *SuiteCommon) TestOverrideConfig(c *C) {
 }
 
 func (s *SuiteCommon) TestOverrideConfigKeep(c *C) {
-	config := &ssh.ClientConfig{
+	config := &stdssh.ClientConfig{
 		User: "foo",
 	}
 
-	target := &ssh.ClientConfig{
+	target := &stdssh.ClientConfig{
 		User: "bar",
 	}
 
@@ -93,12 +95,69 @@ func (s *SuiteCommon) TestDefaultSSHConfigWildcard(c *C) {
 	c.Assert(cmd.getHostWithPort(), Equals, "github.com:22")
 }
 
+func (s *SuiteCommon) TestIgnoreHostKeyCallback(c *C) {
+	uploadPack := &UploadPackSuite{
+		opts: []ssh.Option{
+			ssh.HostKeyPEM(testdata.PEMBytes["ed25519"]),
+		},
+	}
+	uploadPack.SetUpSuite(c)
+	// Use the default client, which does not have a host key callback
+	uploadPack.Client = DefaultClient
+	auth, err := NewPublicKeys("foo", testdata.PEMBytes["rsa"], "")
+	c.Assert(err, IsNil)
+	c.Assert(auth, NotNil)
+	auth.HostKeyCallback = stdssh.InsecureIgnoreHostKey()
+	ep := uploadPack.newEndpoint(c, "bar.git")
+	ps, err := uploadPack.Client.NewUploadPackSession(ep, auth)
+	c.Assert(err, IsNil)
+	c.Assert(ps, NotNil)
+}
+
+func (s *SuiteCommon) TestFixedHostKeyCallback(c *C) {
+	hostKey, err := stdssh.ParsePrivateKey(testdata.PEMBytes["ed25519"])
+	c.Assert(err, IsNil)
+	uploadPack := &UploadPackSuite{
+		opts: []ssh.Option{
+			ssh.HostKeyPEM(testdata.PEMBytes["ed25519"]),
+		},
+	}
+	uploadPack.SetUpSuite(c)
+	// Use the default client, which does not have a host key callback
+	uploadPack.Client = DefaultClient
+	auth, err := NewPublicKeys("foo", testdata.PEMBytes["rsa"], "")
+	c.Assert(err, IsNil)
+	c.Assert(auth, NotNil)
+	auth.HostKeyCallback = stdssh.FixedHostKey(hostKey.PublicKey())
+	ep := uploadPack.newEndpoint(c, "bar.git")
+	ps, err := uploadPack.Client.NewUploadPackSession(ep, auth)
+	c.Assert(err, IsNil)
+	c.Assert(ps, NotNil)
+}
+
+func (s *SuiteCommon) TestFailHostKeyCallback(c *C) {
+	uploadPack := &UploadPackSuite{
+		opts: []ssh.Option{
+			ssh.HostKeyPEM(testdata.PEMBytes["ed25519"]),
+		},
+	}
+	uploadPack.SetUpSuite(c)
+	// Use the default client, which does not have a host key callback
+	uploadPack.Client = DefaultClient
+	auth, err := NewPublicKeys("foo", testdata.PEMBytes["rsa"], "")
+	c.Assert(err, IsNil)
+	c.Assert(auth, NotNil)
+	ep := uploadPack.newEndpoint(c, "bar.git")
+	_, err = uploadPack.Client.NewUploadPackSession(ep, auth)
+	c.Assert(err, NotNil)
+}
+
 func (s *SuiteCommon) TestIssue70(c *C) {
 	uploadPack := &UploadPackSuite{}
 	uploadPack.SetUpSuite(c)
 
-	config := &ssh.ClientConfig{
-		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
+	config := &stdssh.ClientConfig{
+		HostKeyCallback: stdssh.InsecureIgnoreHostKey(),
 	}
 	r := &runner{
 		config: config,

plumbing/transport/ssh/upload_pack_test.go

@@ -25,6 +25,7 @@ import (
 type UploadPackSuite struct {
 	test.UploadPackSuite
 	fixtures.Suite
+	opts []ssh.Option
 
 	port int
 	base string
@@ -57,6 +58,9 @@ func (s *UploadPackSuite) SetUpSuite(c *C) {
 	s.UploadPackSuite.NonExistentEndpoint = s.newEndpoint(c, "non-existent.git")
 
 	server := &ssh.Server{Handler: handlerSSH}
+	for _, opt := range s.opts {
+		opt(server)
+	}
 	go func() {
 		log.Fatal(server.Serve(l))
 	}()