[PATCH v2 1/3] btrfs-progs: add Kernel TLS to btrfs send/receive

[shngmao@gmail.com]

From: Sheng Mao <shngmao@gmail.com>

Currently, btrfs send outputs to a pipe or a file;
btrfs receive inputs from a pipe or a file.
The pipe can be a SSH or a stunnel connection.
btrfs send/receive itself doesn't handle any connection.

Kernel introduces TLS in version 4.13 (referred as ktls).
Ktls provides a transparent TLS 1.2/1.3 connection:
from user space aspect, applications use a normal socket
fd to read/write from/to. This model fits into btrfs send's
design well: btrfs first writes to a pipe and then splices
data from pipe to the final fd (which is a file or pipe).
Ktls simply replaces the final fd with the ktls socket fd.
According to ktls' author, ktls can boost performance for
2~7%. Ktls helps less on receiving side: btrfs receive
processes data in user space. But btrfs receive still can
use transparent TLS layer.

I have implemented ktls for btrfs send/receive. Here are
the key features:

- Use GnuTLS for handshake. OpenSSL is not suitable for this
task, we need to pass IV and key from handshake session to
kernel setting.
- Use PSK (pre-shared key) for handshake. User can use --key
to use a key file or input password on prompt.
- Key file is checked as PEM format first; if it fails, key
file is treated as raw binary file.
- Three TLS modes are supported: none (raw TCP), TLS 1.2 + GCM
128/256, TLS 1.3 + GCM 128.
- DTLS, certificate, Secure Remote Password (SRP) are not
supported yet.

Issue: #326
Signed-off-by: Sheng Mao <shngmao@gmail.com>
---
 common/ktls.c | 702 ++++++++++++++++++++++++++++++++++++++++++++++++++
 common/ktls.h |  57 ++++
 2 files changed, 759 insertions(+)
 create mode 100644 common/ktls.c
 create mode 100644 common/ktls.h

diff --git a/common/ktls.c b/common/ktls.c
new file mode 100644
index 00000000..a4d670e3
--- /dev/null
+++ b/common/ktls.c
@@ -0,0 +1,702 @@
+/*
+ * Copyright (C) 2020 Sheng Mao.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <arpa/inet.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+#include <sys/mman.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <termios.h>
+#include <sys/stat.h>
+
+#include <linux/tls.h>
+
+#include <gnutls/gnutls.h>
+
+#include <common/utils.h>
+
+#include "ktls.h"
+
+enum { KTLS_MAX_PASSWORD_LENGTH = 256, KTLS_MAX_PRIORITY_STRING_LENTH = 256 };
+
+enum {
+	KTLS_STAGE_NOT_HANDSHAKED,
+	KTLS_STAGE_HAS_HANDSHAKED,
+};
+
+enum ktls_tls_mode_t {
+	KTLS_TLS_MODE_NONE = 0,
+	KTLS_TLS_12_128_GCM,
+	KTLS_TLS_13_128_GCM,
+	KTLS_TLS_12_256_GCM
+};
+
+struct ktls_session {
+	gnutls_session_t session;
+	gnutls_certificate_credentials_t crt_cred;
+
+	gnutls_psk_server_credentials_t psk_cred_server;
+	gnutls_psk_client_credentials_t psk_cred_client;
+
+	uint8_t role;
+	uint8_t stage;
+	enum ktls_tls_mode_t tls_mode;
+};
+
+static gnutls_datum_t ktls_psk_username = { 0 };
+static gnutls_datum_t ktls_psk_key = { 0 };
+
+static void ktls_print_logs(int level, const char *msg)
+{
+	if (bconf.verbose >= level)
+		printf("GnuTLS [%d]: %s", level, msg);
+}
+
+int ktls_set_psk_session_from_password_prompt(struct ktls_session *session,
+					      const char *username)
+{
+	struct termios orig_term_flags, passwd_term_flags;
+	char passwd[KTLS_MAX_PASSWORD_LENGTH];
+	int passwd_sz = 0;
+	int stdin_fd = 0;
+
+	if (!session)
+		return EXIT_FAILURE;
+
+	if (session->tls_mode == KTLS_TLS_MODE_NONE)
+		return EXIT_SUCCESS;
+
+	passwd[0] = '\0';
+
+	stdin_fd = fileno(stdin);
+
+	if (!isatty(stdin_fd)) {
+		error("tty needed for password input");
+		return EXIT_FAILURE;
+	}
+
+	tcgetattr(stdin_fd, &orig_term_flags);
+	passwd_term_flags = orig_term_flags;
+	passwd_term_flags.c_lflag &= ~ECHO;
+	passwd_term_flags.c_lflag |= ECHONL;
+
+	if (tcsetattr(stdin_fd, TCSANOW, &passwd_term_flags)) {
+		error("fail to hide password: %s", strerror(errno));
+		return EXIT_FAILURE;
+	}
+
+	printf("password: ");
+	if (!fgets(passwd, sizeof(passwd), stdin)) {
+		error("no password read");
+		return EXIT_FAILURE;
+	}
+
+	if (tcsetattr(fileno(stdin), TCSANOW, &orig_term_flags)) {
+		error("fail to reset tty: %s", strerror(errno));
+		return EXIT_FAILURE;
+	}
+
+	passwd_sz = strlen(passwd);
+	if (passwd_sz <= 0) {
+		error("no password read");
+		return EXIT_FAILURE;
+	}
+	if (passwd[passwd_sz - 1] == '\n') {
+		passwd[passwd_sz - 1] = '\0';
+		passwd_sz--;
+	}
+
+	return ktls_set_psk_session(session, username,
+				    (const unsigned char *)passwd, passwd_sz);
+}
+
+int ktls_set_psk_session_from_keyfile(struct ktls_session *session,
+				      const char *username,
+				      const char *key_file)
+{
+	int rc = GNUTLS_E_SUCCESS;
+	struct stat file_stat;
+	size_t sz = 0;
+	FILE *fp = NULL;
+	gnutls_datum_t input = { NULL, 0UL };
+	gnutls_datum_t output = { NULL, 0UL };
+
+	if (!session)
+		goto cleanup;
+
+	if (session->tls_mode == KTLS_TLS_MODE_NONE)
+		return EXIT_SUCCESS;
+
+	if (stat(key_file, &file_stat)) {
+		error("fail to open keyfile: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	fp = fopen(key_file, "r");
+	if (!fp) {
+		error("fail to open keyfile: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	input.size = file_stat.st_size;
+
+	input.data = gnutls_malloc(input.size);
+
+	sz = fread(input.data, 1, input.size, fp);
+
+	if (sz != input.size) {
+		error("fail to read PEM");
+		goto cleanup;
+	}
+
+	rc = gnutls_pem_base64_decode2(NULL, &input, &output);
+	if (rc != GNUTLS_E_SUCCESS) {
+		error("Error! fail to decode PEM: %s", gnutls_strerror(rc));
+		goto cleanup;
+	}
+
+	return ktls_set_psk_session(session, username, output.data,
+				    output.size);
+
+cleanup:
+	return EXIT_FAILURE;
+}
+
+struct ktls_session *ktls_create_session(bool is_sender)
+{
+	struct ktls_session *session = NULL;
+
+	session = (struct ktls_session *)malloc(sizeof(struct ktls_session));
+	explicit_bzero(session, sizeof(*session));
+
+	gnutls_global_init();
+
+	session->role = is_sender ? GNUTLS_CLIENT : GNUTLS_SERVER;
+	session->stage = KTLS_STAGE_NOT_HANDSHAKED;
+
+	gnutls_init(&session->session, session->role);
+
+	gnutls_global_set_log_level(bconf.verbose);
+	gnutls_global_set_log_function(ktls_print_logs);
+
+	return session;
+}
+
+void ktls_destroy_session(struct ktls_session *session)
+{
+	if (!session)
+		return;
+
+	if (session->crt_cred)
+		gnutls_certificate_free_credentials(session->crt_cred);
+
+	if (session->psk_cred_server)
+		gnutls_psk_free_server_credentials(session->psk_cred_server);
+
+	if (session->psk_cred_client)
+		gnutls_psk_free_client_credentials(session->psk_cred_client);
+
+	if (session->session) {
+		if (session->stage == KTLS_STAGE_HAS_HANDSHAKED)
+			gnutls_bye(session->session, GNUTLS_SHUT_RDWR);
+		gnutls_deinit(session->session);
+	}
+
+	gnutls_global_deinit();
+
+	explicit_bzero(session, sizeof(*session));
+}
+
+static int ktls_connect_or_bind(int *sock, bool is_sender, int protocol,
+				struct sockaddr *serv_addr, size_t serv_addr_sz)
+{
+	*sock = 0;
+
+	*sock = socket(protocol, SOCK_STREAM, 0);
+	if (*sock == KTLS_INVALID_FD) {
+		error("could not create socket: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	if (is_sender) {
+		if (connect(*sock, serv_addr, serv_addr_sz)) {
+			error("fail to connect to server: %s", strerror(errno));
+			goto cleanup;
+		}
+		return EXIT_SUCCESS;
+	}
+
+	if (setsockopt(*sock, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 },
+		       sizeof(int))) {
+		error("fail to connect to server: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	if (bind(*sock, serv_addr, serv_addr_sz) || listen(*sock, 1)) {
+		error("fail to serve as server: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	return EXIT_SUCCESS;
+
+cleanup:
+	if (*sock >= 0)
+		close(*sock);
+	return EXIT_FAILURE;
+}
+
+static int ktls_connect_domain(int *sock, bool is_sender, const char *host,
+			       const uint16_t port)
+{
+	struct addrinfo hints = { 0 }, *res = NULL;
+	int rc = 0;
+	struct sockaddr_in addr4;
+	struct sockaddr_in6 addr6;
+
+	memset(&hints, 0, sizeof(hints));
+
+	hints.ai_family = PF_UNSPEC;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_flags |= AI_CANONNAME;
+
+	if (getaddrinfo(host, NULL, &hints, &res)) {
+		error("fail to get address info: %s", strerror(errno));
+		return EXIT_FAILURE;
+	}
+
+	while (res) {
+		switch (res->ai_family) {
+		case AF_INET:
+			explicit_bzero(&addr4, sizeof(addr4));
+			addr4.sin_addr =
+				((struct sockaddr_in *)res->ai_addr)->sin_addr;
+			addr4.sin_port = port;
+			addr4.sin_family = res->ai_family;
+			if (!ktls_connect_or_bind(
+				    sock, is_sender, res->ai_family,
+				    (struct sockaddr *)&addr4, sizeof(addr4))) {
+				goto cleanup;
+			}
+			break;
+		case AF_INET6:
+			explicit_bzero(&addr6, sizeof(addr6));
+			addr6.sin6_addr =
+				((struct sockaddr_in6 *)res->ai_addr)->sin6_addr;
+			addr6.sin6_port = port;
+			addr6.sin6_family = res->ai_family;
+			if (!ktls_connect_or_bind(
+				    sock, is_sender, res->ai_family,
+				    (struct sockaddr *)&addr6, sizeof(addr6))) {
+				goto cleanup;
+			}
+			break;
+		}
+		res = res->ai_next;
+	}
+
+	freeaddrinfo(res);
+	return EXIT_FAILURE;
+
+cleanup:
+	freeaddrinfo(res);
+	return rc;
+}
+
+static int ktls_connect_ip(int *sock, bool is_sender, const char *host,
+			   const uint16_t port)
+{
+	struct sockaddr_in addr4;
+	struct sockaddr_in6 addr6;
+	struct sockaddr *serv_addr = NULL;
+	size_t serv_addr_sz = 0;
+	sa_family_t protol = AF_INET;
+
+	explicit_bzero(&addr4, sizeof(addr4));
+	explicit_bzero(&addr6, sizeof(addr6));
+
+	if (inet_pton(AF_INET, host, &addr4.sin_addr) == 1) {
+		serv_addr = (struct sockaddr *)&addr4;
+		serv_addr_sz = sizeof(addr4);
+		protol = addr4.sin_family = AF_INET;
+		addr4.sin_port = port;
+	}
+
+	if (!serv_addr && inet_pton(AF_INET6, host, &addr6.sin6_addr) == 1) {
+		serv_addr = (struct sockaddr *)&addr6;
+		serv_addr_sz = sizeof(addr6);
+		protol = addr6.sin6_family = AF_INET6;
+		addr6.sin6_port = port;
+	}
+
+	if (!serv_addr)
+		return KTLS_INVALID_FD;
+
+	return ktls_connect_or_bind(sock, is_sender, protol, serv_addr,
+				    serv_addr_sz);
+}
+
+int ktls_set_tls_mode(struct ktls_session *session, const char *mode)
+{
+	if (!session)
+		return EXIT_FAILURE;
+
+	if (!strcmp("none", mode))
+		session->tls_mode = KTLS_TLS_MODE_NONE;
+	else if (!strcmp("tls_12_128_gcm", mode))
+		session->tls_mode = KTLS_TLS_12_128_GCM;
+	else if (!strcmp("tls_13_128_gcm", mode))
+		session->tls_mode = KTLS_TLS_13_128_GCM;
+	else if (!strcmp("tls_12_256_gcm", mode))
+		session->tls_mode = KTLS_TLS_12_256_GCM;
+	else {
+		error("unknown tls mode: %s", mode);
+		return EXIT_FAILURE;
+	}
+	return EXIT_SUCCESS;
+}
+
+#define INIT_GCM_WITH_MODE(V, X)                                               \
+	{                                                                      \
+		struct tls12_crypto_info_aes_gcm_##X crypto_info;              \
+\
+		crypto_info.info.version = TLS_##V##_VERSION;                  \
+		crypto_info.info.cipher_type = TLS_CIPHER_AES_GCM_##X;         \
+		memcpy(crypto_info.iv, seq_number,                             \
+		       TLS_CIPHER_AES_GCM_##X##_IV_SIZE);                      \
+		memcpy(crypto_info.rec_seq, seq_number,                        \
+		       TLS_CIPHER_AES_GCM_##X##_REC_SEQ_SIZE);                 \
+		if (cipher_key.size != TLS_CIPHER_AES_GCM_##X##_KEY_SIZE) {    \
+			error("mismatch in send key size: %d != %d\n",         \
+			      cipher_key.size,                                 \
+			      TLS_CIPHER_AES_GCM_##X##_KEY_SIZE);              \
+			goto cleanup;                                          \
+		}                                                              \
+		memcpy(crypto_info.key, cipher_key.data,                       \
+		       TLS_CIPHER_AES_GCM_##X##_KEY_SIZE);                     \
+		memcpy(crypto_info.salt, iv.data,                              \
+		       TLS_CIPHER_AES_GCM_##X##_SALT_SIZE);                    \
+		if (setsockopt(sock, SOL_TLS, is_sender ? TLS_TX : TLS_RX,     \
+			       &crypto_info, sizeof(crypto_info))) {           \
+			error("fail to set kernel tls: %s", strerror(errno));  \
+			goto cleanup;                                          \
+		}                                                              \
+	}
+
+int ktls_handshake_tls(struct ktls_session *session, int sock)
+{
+	int rc = 0;
+	bool is_sender = false;
+	int handshake_retry = 3;
+	char tls_priority_list[KTLS_MAX_PRIORITY_STRING_LENTH];
+	const char *tls_priority_templ =
+		"NONE:+MAC-ALL:+COMP-NULL:+SIGN-ALL:+GROUP-ALL:+ECDHE-PSK:+DHE-PSK:%s:%s";
+	const char *tls_priority_ver_mode = NULL;
+
+	gnutls_datum_t mac_key;
+	gnutls_datum_t iv;
+	gnutls_datum_t cipher_key;
+	unsigned char seq_number[8];
+
+	if (!session || !session->session)
+		return EXIT_FAILURE;
+
+	switch (session->tls_mode) {
+	case KTLS_TLS_MODE_NONE:
+		return EXIT_SUCCESS;
+	case KTLS_TLS_12_128_GCM:
+		tls_priority_ver_mode = "+VERS-TLS1.2:+AES-128-GCM";
+		break;
+	case KTLS_TLS_13_128_GCM:
+		tls_priority_ver_mode = "+VERS-TLS1.3:+AES-128-GCM";
+		break;
+	case KTLS_TLS_12_256_GCM:
+		tls_priority_ver_mode = "+VERS-TLS1.2:+AES-256-GCM";
+		break;
+	default:
+		error("unknown tls mode");
+		goto cleanup;
+	}
+
+	is_sender = session->role == GNUTLS_CLIENT;
+
+	if (is_sender && session->psk_cred_client) {
+		rc = gnutls_credentials_set(session->session, GNUTLS_CRD_PSK,
+					    session->psk_cred_client);
+		if (rc != GNUTLS_E_SUCCESS) {
+			error("fail to set PSK for client: %s",
+			      gnutls_strerror(rc));
+			goto cleanup;
+		}
+	}
+
+	if (!is_sender && session->psk_cred_server) {
+		rc = gnutls_credentials_set(session->session, GNUTLS_CRD_PSK,
+					    session->psk_cred_server);
+		if (rc != GNUTLS_E_SUCCESS) {
+			error("fail to set PSK for server: %s",
+			      gnutls_strerror(rc));
+			goto cleanup;
+		}
+	}
+
+	if (session->crt_cred) {
+		rc = gnutls_credentials_set(session->session,
+					    GNUTLS_CRD_CERTIFICATE,
+					    session->crt_cred);
+
+		if (rc == GNUTLS_E_SUCCESS) {
+			error("fail to set certificate: %s",
+			      gnutls_strerror(rc));
+			goto cleanup;
+		}
+	}
+
+	snprintf(tls_priority_list, KTLS_MAX_PRIORITY_STRING_LENTH,
+		 tls_priority_templ,
+		 is_sender ? "+CTYPE-CLI-ALL" : "+CTYPE-SRV-ALL",
+		 tls_priority_ver_mode);
+
+	rc = gnutls_priority_set_direct(session->session, tls_priority_list,
+					NULL);
+	if (rc != GNUTLS_E_SUCCESS) {
+		error("fail to set priority: %s", gnutls_strerror(rc));
+		goto cleanup;
+	}
+
+	gnutls_transport_set_int(session->session, sock);
+
+	gnutls_handshake_set_timeout(session->session,
+				     GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
+
+	do {
+		if (handshake_retry < 0) {
+			error("exhaust retries on handshake");
+			break;
+		}
+		rc = gnutls_handshake(session->session);
+		handshake_retry--;
+	} while (rc < 0 && !gnutls_error_is_fatal(rc));
+
+	if (gnutls_error_is_fatal(rc)) {
+		error("fail on handshake: %s", gnutls_strerror(rc));
+		goto cleanup;
+	}
+	if (bconf.verbose > 0) {
+		char *desc = gnutls_session_get_desc(session->session);
+
+		printf("TLS session info: %s\n", desc);
+		gnutls_free(desc);
+	}
+
+	session->stage = KTLS_STAGE_HAS_HANDSHAKED;
+
+	rc = gnutls_record_get_state(session->session, is_sender ? 0 : 1,
+				     &mac_key, &iv, &cipher_key, seq_number);
+	if (rc != GNUTLS_E_SUCCESS) {
+		error("fail on retrieve TLS record: %s", gnutls_strerror(rc));
+		goto cleanup;
+	}
+
+	if (setsockopt(sock, SOL_TCP, TCP_ULP, "tls", sizeof("tls"))) {
+		error("fail to set kernel TLS on socket: %s", strerror(errno));
+		goto cleanup;
+	}
+
+	switch (session->tls_mode) {
+	case KTLS_TLS_12_128_GCM:
+		INIT_GCM_WITH_MODE(1_2, 128);
+		break;
+	case KTLS_TLS_13_128_GCM:
+		INIT_GCM_WITH_MODE(1_3, 128);
+		break;
+	case KTLS_TLS_12_256_GCM:
+		INIT_GCM_WITH_MODE(1_2, 256);
+		break;
+	default:
+		error("unknown tls mode");
+		goto cleanup;
+	}
+
+	if (bconf.verbose > 0)
+		fprintf(stderr, "ktls init done\n");
+
+	return EXIT_SUCCESS;
+
+cleanup:
+	return EXIT_FAILURE;
+}
+
+static int ktls_cp_datum(gnutls_datum_t *to, const gnutls_datum_t *from)
+{
+	if (!to || !from)
+		return EXIT_FAILURE;
+
+	to->size = from->size;
+	to->data = (unsigned char *)gnutls_malloc(to->size);
+	memmove(to->data, from->data, to->size);
+
+	return EXIT_SUCCESS;
+}
+
+static int ktls_cmp_datum(const gnutls_datum_t *lhs, const gnutls_datum_t *rhs)
+{
+	if (!lhs && !rhs)
+		return EXIT_SUCCESS;
+
+	if (!lhs || !rhs)
+		return EXIT_FAILURE;
+
+	if (lhs->size != rhs->size)
+		return EXIT_FAILURE;
+
+	return memcmp(lhs->data, rhs->data, lhs->size);
+}
+
+static int ktls_set_datum(gnutls_datum_t *to, const unsigned char *from,
+			  int from_size)
+{
+	if (!to || !from || !from_size)
+		return EXIT_FAILURE;
+
+	if (from_size < 0)
+		from_size = strlen((const char *)from);
+
+	to->size = from_size;
+	to->data = (unsigned char *)gnutls_malloc(to->size);
+	memmove(to->data, from, from_size);
+
+	return EXIT_SUCCESS;
+}
+
+static int tls_psk_client_callback(gnutls_session_t session,
+				   gnutls_datum_t *username,
+				   gnutls_datum_t *key)
+{
+	if (ktls_cp_datum(username, &ktls_psk_username) ||
+	    ktls_cp_datum(key, &ktls_psk_key))
+		return EXIT_FAILURE;
+
+	return EXIT_SUCCESS;
+}
+
+static int tls_psk_server_callback(gnutls_session_t session,
+				   const gnutls_datum_t *username,
+				   gnutls_datum_t *key)
+{
+	if (ktls_cmp_datum(username, &ktls_psk_username) ||
+	    ktls_cp_datum(key, &ktls_psk_key))
+		return EXIT_FAILURE;
+
+	return EXIT_SUCCESS;
+}
+
+int ktls_set_psk_session(struct ktls_session *session, const char *username,
+			 const unsigned char *passwd, const size_t sz_passwd)
+{
+	bool is_sender = false;
+	int rc = 0;
+
+	if (!session || !session->session)
+		goto cleanup;
+
+	is_sender = session->role == GNUTLS_CLIENT;
+
+	if (!is_sender && !session->psk_cred_server) {
+		rc = gnutls_psk_allocate_server_credentials(
+			&session->psk_cred_server);
+		if (rc != GNUTLS_E_SUCCESS) {
+			error("fail on set psk for server: %s",
+			      gnutls_strerror(rc));
+			goto cleanup;
+		}
+		gnutls_psk_set_server_credentials_function2(
+			session->psk_cred_server, tls_psk_server_callback);
+	}
+
+	if (is_sender && !session->psk_cred_client) {
+		rc = gnutls_psk_allocate_client_credentials(
+			&session->psk_cred_client);
+		if (rc != GNUTLS_E_SUCCESS) {
+			error("fail on set psk for client: %s",
+			      gnutls_strerror(rc));
+			goto cleanup;
+		}
+		gnutls_psk_set_client_credentials_function2(
+			session->psk_cred_client, tls_psk_client_callback);
+	}
+
+	if (!ktls_psk_key.size)
+		gnutls_free(ktls_psk_key.data);
+
+	if (!ktls_psk_username.size)
+		gnutls_free(ktls_psk_username.data);
+
+	if (ktls_set_datum(&ktls_psk_username, (const unsigned char *)username,
+			   -1) ||
+	    ktls_set_datum(&ktls_psk_key, passwd, sz_passwd))
+		goto cleanup;
+
+	return EXIT_SUCCESS;
+
+cleanup:
+	return EXIT_FAILURE;
+}
+
+int ktls_create_sock_oneshot(struct ktls_session *session, const char *host,
+			     const char *port)
+{
+	int sock = 0;
+	int nport = 0;
+	bool is_sender;
+
+	if (!session || !session->session)
+		return EXIT_FAILURE;
+
+	is_sender = session->role == GNUTLS_CLIENT;
+
+	nport = atoi(port);
+
+	if (nport >= 0 && nport <= 65535)
+		nport = htons((uint16_t)nport);
+
+	if (ktls_connect_ip(&sock, is_sender, host, (uint16_t)nport))
+		if (ktls_connect_domain(&sock, is_sender, host, nport))
+			goto cleanup;
+
+	if (!is_sender) {
+		int accepted_sock = KTLS_INVALID_FD;
+
+		accepted_sock = accept(sock, (struct sockaddr *)NULL, NULL);
+		close(sock);
+		sock = accepted_sock;
+	}
+
+	if (ktls_handshake_tls(session, sock))
+		goto cleanup;
+
+	return sock;
+
+cleanup:
+	close(sock);
+	return KTLS_INVALID_FD;
+}
diff --git a/common/ktls.h b/common/ktls.h
new file mode 100644
index 00000000..d744e18e
--- /dev/null
+++ b/common/ktls.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2020 Sheng Mao.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef __BTRFS_KTLS_H__
+#define __BTRFS_KTLS_H__
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct ktls_session;
+
+enum { KTLS_INVALID_FD = -1 };
+
+struct ktls_session *ktls_create_session(bool is_sender);
+void ktls_destroy_session(struct ktls_session *session);
+
+// ktls_set_psk_session sets PSK (pre-shared key). username is NULL-terminated
+// string; passwd is sized string. Memory of both strings are managed by
+// caller. currently, this API only allows to set PSK before calling
+// ktls_handshake_*()
+int ktls_set_psk_session(struct ktls_session *session, const char *username,
+			 const unsigned char *passwd, const size_t sz_passwd);
+
+int ktls_set_psk_session_from_password_prompt(struct ktls_session *session,
+					      const char *username);
+
+int ktls_set_psk_session_from_keyfile(struct ktls_session *session,
+				      const char *username,
+				      const char *key_file);
+
+int ktls_set_tls_mode(struct ktls_session *session, const char *mode);
+
+int ktls_handshake_tls(struct ktls_session *session, int sock);
+
+// ktls_create_sock_oneshot returns a sock fd on success.
+int ktls_create_sock_oneshot(struct ktls_session *session, const char *host,
+			     const char *port);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // __BTRFS_KTLS_H__
-- 
2.29.2