plumbing: support setting custom host key algorithms along with host key callback

Author: Javier-varez

Diff for: plumbing/transport/ssh/auth_method.go

@@ -54,7 +54,7 @@ func (a *KeyboardInteractive) String() string {
 }
 
 func (a *KeyboardInteractive) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
+	return a.SetHostKeyCallbackAndAlgorithms(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{
 			a.Challenge,
@@ -78,7 +78,7 @@ func (a *Password) String() string {
 }
 
 func (a *Password) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
+	return a.SetHostKeyCallbackAndAlgorithms(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.Password(a.Password)},
 	})
@@ -101,7 +101,7 @@ func (a *PasswordCallback) String() string {
 }
 
 func (a *PasswordCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
+	return a.SetHostKeyCallbackAndAlgorithms(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
 	})
@@ -150,7 +150,7 @@ func (a *PublicKeys) String() string {
 }
 
 func (a *PublicKeys) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
+	return a.SetHostKeyCallbackAndAlgorithms(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
 	})
@@ -211,7 +211,7 @@ func (a *PublicKeysCallback) String() string {
 }
 
 func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
+	return a.SetHostKeyCallbackAndAlgorithms(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
 	})
@@ -301,20 +301,23 @@ func filterKnownHostsFiles(files ...string) ([]string, error) {
 }
 
 // HostKeyCallbackHelper is a helper that provides common functionality to
-// configure HostKeyCallback into a ssh.ClientConfig.
+// configure HostKeyCallback and HostKeyAlgorithms into a ssh.ClientConfig.
 type HostKeyCallbackHelper struct {
 	// HostKeyCallback is the function type used for verifying server keys.
 	// If nil, a default callback will be created using NewKnownHostsDb
 	// without argument.
 	HostKeyCallback ssh.HostKeyCallback
 
+	// HostKeyAlgorithms is a list of supported host key algorithms that will
+	// be used for host key verification.
+	HostKeyAlgorithms []string
 }
 
-// SetHostKeyCallback sets the field HostKeyCallback in the given cfg.
-// If the host key callback is empty it is left empty. It will be handled
-// by the dial method by falling back to knownhosts.
-func (m *HostKeyCallbackHelper) SetHostKeyCallback(cfg *ssh.ClientConfig) (*ssh.ClientConfig, error) {
-
+// SetHostKeyCallbackAndAlgorithms sets the field HostKeyCallback and HostKeyAlgorithms in the given cfg.
+// If the host key callback or algorithms is empty it is left empty. It will be handled by the dial method,
+// falling back to knownhosts.
+func (m *HostKeyCallbackHelper) SetHostKeyCallbackAndAlgorithms(cfg *ssh.ClientConfig) (*ssh.ClientConfig, error) {
 	cfg.HostKeyCallback = m.HostKeyCallback
+	cfg.HostKeyAlgorithms = m.HostKeyAlgorithms
 	return cfg, nil
 }

Diff for: plumbing/transport/ssh/common_test.go

@@ -129,12 +129,35 @@ func (s *SuiteCommon) TestFixedHostKeyCallback(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(auth, NotNil)
 	auth.HostKeyCallback = stdssh.FixedHostKey(hostKey.PublicKey())
+	auth.HostKeyAlgorithms = []string{"ssh-ed25519"}
 	ep := uploadPack.newEndpoint(c, "bar.git")
 	ps, err := uploadPack.Client.NewUploadPackSession(ep, auth)
 	c.Assert(err, IsNil)
 	c.Assert(ps, NotNil)
 }
 
+func (s *SuiteCommon) TestFixedHostKeyCallbackUnexpectedAlgorithm(c *C) {
+	hostKey, err := stdssh.ParsePrivateKey(testdata.PEMBytes["ed25519"])
+	c.Assert(err, IsNil)
+	uploadPack := &UploadPackSuite{
+		opts: []ssh.Option{
+			ssh.HostKeyPEM(testdata.PEMBytes["rsa"]),
+		},
+	}
+	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())
+	auth.HostKeyAlgorithms = []string{"ssh-ed25519"}
+	ep := uploadPack.newEndpoint(c, "bar.git")
+	ps, err := uploadPack.Client.NewUploadPackSession(ep, auth)
+	c.Assert(err, NotNil)
+	c.Assert(ps, IsNil)
+}
+
 func (s *SuiteCommon) TestFailHostKeyCallback(c *C) {
 	uploadPack := &UploadPackSuite{
 		opts: []ssh.Option{