Merge pull request #2273 from jacquesg/ssh-interactive

Add support for SSH keyboard-interactive authentication

include/git2/transport.h

@@ -41,6 +41,9 @@ typedef enum {
 
 	/* git_cred_default */
 	GIT_CREDTYPE_DEFAULT = (1u << 3),
+
+	/* git_cred_ssh_interactive */
+	GIT_CREDTYPE_SSH_INTERACTIVE = (1u << 4),
 } git_credtype_t;
 
 /* The base structure for all credential types */
@@ -60,8 +63,10 @@ typedef struct {
 
 #ifdef GIT_SSH
 typedef LIBSSH2_USERAUTH_PUBLICKEY_SIGN_FUNC((*git_cred_sign_callback));
+typedef LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC((*git_cred_ssh_interactive_callback));
 #else
 typedef int (*git_cred_sign_callback)(void *, ...);
+typedef int (*git_cred_ssh_interactive_callback)(void *, ...);
 #endif
 
 /**
@@ -76,6 +81,16 @@ typedef struct git_cred_ssh_key {
 } git_cred_ssh_key;
 
 /**
+ * Keyboard-interactive based ssh authentication
+ */
+typedef struct git_cred_ssh_interactive {
+	git_cred parent;
+	char *username;
+	git_cred_ssh_interactive_callback prompt_callback;
+	void *payload;
+} git_cred_ssh_interactive;
+
+/**
  * A key with a custom signature function
  */
 typedef struct git_cred_ssh_custom {
@@ -83,8 +98,8 @@ typedef struct git_cred_ssh_custom {
 	char *username;
 	char *publickey;
 	size_t publickey_len;
-	void *sign_callback;
-	void *sign_data;
+	git_cred_sign_callback sign_callback;
+	void *payload;
 } git_cred_ssh_custom;
 
 /** A key for NTLM/Kerberos "default" credentials */
@@ -131,6 +146,21 @@ GIT_EXTERN(int) git_cred_ssh_key_new(
 	const char *passphrase);
 
 /**
+ * Create a new ssh keyboard-interactive based credential object.
+ * The supplied credential parameter will be internally duplicated.
+ *
+ * @param username Username to use to authenticate.
+ * @param prompt_callback The callback method used for prompts.
+ * @param payload Additional data to pass to the callback.
+ * @return 0 for success or an error code for failure.
+ */
+GIT_EXTERN(int) git_cred_ssh_interactive_new(
+	git_cred **out,
+	const char *username,
+	git_cred_ssh_interactive_callback prompt_callback,
+	void *payload);
+
+/**
  * Create a new ssh key credential object used for querying an ssh-agent.
  * The supplied credential parameter will be internally duplicated.
  *
@@ -156,8 +186,8 @@ GIT_EXTERN(int) git_cred_ssh_key_from_agent(
  * @param username username to use to authenticate
  * @param publickey The bytes of the public key.
  * @param publickey_len The length of the public key in bytes.
- * @param sign_fn The callback method to sign the data during the challenge.
- * @param sign_data The data to pass to the sign function.
+ * @param sign_callback The callback method to sign the data during the challenge.
+ * @param payload Additional data to pass to the callback.
  * @return 0 for success or an error code for failure
  */
 GIT_EXTERN(int) git_cred_ssh_custom_new(
@@ -165,8 +195,8 @@ GIT_EXTERN(int) git_cred_ssh_custom_new(
 	const char *username,
 	const char *publickey,
 	size_t publickey_len,
-	git_cred_sign_callback sign_fn,
-	void *sign_data);
+	git_cred_sign_callback sign_callback,
+	void *payload);
 
 /**
  * Create a "default" credential usable for Negotiate mechanisms like NTLM

src/transports/cred.c

@@ -30,7 +30,6 @@ static void plaintext_free(struct git_cred *cred)
 		git__free(c->password);
 	}
 
-	git__memzero(c, sizeof(*c));
 	git__free(c);
 }
 
@@ -73,8 +72,13 @@ static void ssh_key_free(struct git_cred *cred)
 		(git_cred_ssh_key *)cred;
 
 	git__free(c->username);
-	git__free(c->publickey);
-	git__free(c->privatekey);
+
+	if (c->privatekey) {
+		/* Zero the memory which previously held the private key */
+		size_t key_len = strlen(c->privatekey);
+		git__memzero(c->privatekey, key_len);
+		git__free(c->privatekey);
+	}
 
 	if (c->passphrase) {
 		/* Zero the memory which previously held the passphrase */
@@ -83,7 +87,22 @@ static void ssh_key_free(struct git_cred *cred)
 		git__free(c->passphrase);
 	}
 
-	git__memzero(c, sizeof(*c));
+	if (c->publickey) {
+		/* Zero the memory which previously held the public key */
+		size_t key_len = strlen(c->publickey);
+		git__memzero(c->publickey, key_len);
+		git__free(c->publickey);
+	}
+
+	git__free(c);
+}
+
+static void ssh_interactive_free(struct git_cred *cred)
+{
+	git_cred_ssh_interactive *c = (git_cred_ssh_interactive *)cred;
+
+	git__free(c->username);
+
 	git__free(c);
 }
 
@@ -92,9 +111,14 @@ static void ssh_custom_free(struct git_cred *cred)
 	git_cred_ssh_custom *c = (git_cred_ssh_custom *)cred;
 
 	git__free(c->username);
-	git__free(c->publickey);
 
-	git__memzero(c, sizeof(*c));
+	if (c->publickey) {
+		/* Zero the memory which previously held the publickey */
+		size_t key_len = strlen(c->publickey);
+		git__memzero(c->publickey, key_len);
+		git__free(c->publickey);
+	}
+
 	git__free(c);
 }
 
@@ -142,6 +166,32 @@ int git_cred_ssh_key_new(
 	return 0;
 }
 
+int git_cred_ssh_interactive_new(
+	git_cred **out,
+	const char *username,
+	git_cred_ssh_interactive_callback prompt_callback,
+	void *payload)
+{
+	git_cred_ssh_interactive *c;
+
+	assert(out && username && prompt_callback);
+
+	c = git__calloc(1, sizeof(git_cred_ssh_interactive));
+	GITERR_CHECK_ALLOC(c);
+
+	c->parent.credtype = GIT_CREDTYPE_SSH_INTERACTIVE;
+	c->parent.free = ssh_interactive_free;
+
+	c->username = git__strdup(username);
+	GITERR_CHECK_ALLOC(c->username);
+
+	c->prompt_callback = prompt_callback;
+	c->payload = payload;
+
+	*out = &c->parent;
+	return 0;
+}
+
 int git_cred_ssh_key_from_agent(git_cred **cred, const char *username) {
 	git_cred_ssh_key *c;
 
@@ -168,7 +218,7 @@ int git_cred_ssh_custom_new(
 	const char *publickey,
 	size_t publickey_len,
 	git_cred_sign_callback sign_callback,
-	void *sign_data)
+	void *payload)
 {
 	git_cred_ssh_custom *c;
 
@@ -192,7 +242,7 @@ int git_cred_ssh_custom_new(
 
 	c->publickey_len = publickey_len;
 	c->sign_callback = sign_callback;
-	c->sign_data = sign_data;
+	c->payload = payload;
 
 	*cred = &c->parent;
 	return 0;

src/transports/ssh.c

@@ -310,7 +310,28 @@ static int _git_ssh_authenticate_session(
 
 			rc = libssh2_userauth_publickey(
 				session, c->username, (const unsigned char *)c->publickey,
-				c->publickey_len, c->sign_callback, &c->sign_data);
+				c->publickey_len, c->sign_callback, &c->payload);
+			break;
+		}
+		case GIT_CREDTYPE_SSH_INTERACTIVE: {
+			void **abstract = libssh2_session_abstract(session);
+			git_cred_ssh_interactive *c = (git_cred_ssh_interactive *)cred;
+
+			/* ideally, we should be able to set this by calling
+			 * libssh2_session_init_ex() instead of libssh2_session_init().
+			 * libssh2's API is inconsistent here i.e. libssh2_userauth_publickey()
+			 * allows you to pass the `abstract` as part of the call, whereas
+			 * libssh2_userauth_keyboard_interactive() does not!
+			 *
+			 * The only way to set the `abstract` pointer is by calling
+			 * libssh2_session_abstract(), which will replace the existing
+			 * pointer as is done below. This is safe for now (at time of writing),
+			 * but may not be valid in future.
+			 */
+			*abstract = c->payload;
+
+			rc = libssh2_userauth_keyboard_interactive(
+				session, c->username, c->prompt_callback);
 			break;
 		}
 		default:
@@ -397,6 +418,7 @@ static int _git_ssh_setup_conn(
 				&t->cred, t->owner->url, user,
 				GIT_CREDTYPE_USERPASS_PLAINTEXT |
 				GIT_CREDTYPE_SSH_KEY |
+				GIT_CREDTYPE_SSH_INTERACTIVE |
 				GIT_CREDTYPE_SSH_CUSTOM,
 				t->owner->cred_acquire_payload) < 0)
 			goto on_error;