Connections are now using tokens

client.c

@@ -32,6 +32,7 @@
 #include <unistd.h>
 
 #include "tmux.h"
+#include "tmate.h"
 
 struct imsgbuf	client_ibuf;
 struct event	client_event;
@@ -206,8 +207,8 @@ client_main(int argc, char **argv, int flags)
 	}
 
 #ifdef TMATE_SLAVE
-	cmdflags &= ~CMD_STARTSERVER;
-#endif
+	fd = tmux_socket_fd;
+#else
 
 	/*
 	 * Check if this could be a nested session, if the command can't nest:
@@ -227,6 +228,7 @@ client_main(int argc, char **argv, int flags)
 		fprintf(stderr, "failed to connect to server\n");
 		return (1);
 	}
+#endif
 
 	/* Set process title, log and signals now this is the client. */
 #ifdef HAVE_SETPROCTITLE
@@ -293,8 +295,9 @@ client_main(int argc, char **argv, int flags)
 
 	/* Print the exit message, if any, and exit. */
 	if (client_attached) {
-		if (client_exitreason != CLIENT_EXIT_NONE && !login_shell)
-			printf("[%s]\n", client_exit_message());
+		if (client_exitreason != CLIENT_EXIT_NONE && !login_shell) {
+			printf("[%s]\r\n", client_exit_message());
+		}
 
 		ppid = getppid();
 		if (client_exittype == MSG_DETACHKILL && ppid > 1)

server.c

@@ -97,9 +97,7 @@ server_create_socket(void)
 		fatal("listen failed");
 	setblocking(fd, 0);
 
-	server_update_socket();
-
-	return (fd);
+	server_update_socket(); return (fd);
 }
 
 /* Fork new server. */
@@ -162,9 +160,10 @@ server_start(int lockfd, char *lockfile)
 	setproctitle("server (%s)", socket_path);
 #endif
 
+#ifdef TMATE_SLAVE
+	server_fd = tmux_socket_fd;
+#else
 	server_fd = server_create_socket();
-
-#ifndef TMATE_SLAVE
 	server_client_create(pair[1]);
 
 	unlink(lockfile);
@@ -397,10 +396,12 @@ server_signal_callback(int sig, unused short events, unused void *data)
 		server_child_signal();
 		break;
 	case SIGUSR1:
+#ifndef TMATE_SLAVE
 		event_del(&server_ev_accept);
 		close(server_fd);
 		server_fd = server_create_socket();
 		server_add_accept(0);
+#endif
 		break;
 	}
 }

tmate-slave.c

@@ -1,8 +1,16 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <libssh/libssh.h>
 #include "tmate.h"
 
+struct tmate_encoder *tmate_encoder;
+int tmux_socket_fd;
+const char *tmate_session_token;
+
+extern int server_create_socket(void);
+extern int client_connect(char *path, int start_server);
+
 static void usage(void)
 {
 	fprintf(stderr, "usage: tmate-slave [-p PORT]\n");
@@ -14,8 +22,6 @@ int main(int argc, char **argv)
 	int port = 22;
 	char *log_path = NULL; /* stderr */
 
-	strcpy(socket_path, "/tmp/tmate-slave");
-
 	while ((opt = getopt(argc, argv, "p:l:v")) != -1) {
 		switch (opt) {
 		case 'p':
@@ -38,16 +44,62 @@ int main(int argc, char **argv)
 	return 0;
 }
 
-struct tmate_encoder *tmate_encoder;
-
-void tmate_spawn_slave_server(struct tmate_ssh_client *client)
+static void set_session_token(const char *token)
 {
+	tmate_session_token = xstrdup(token);
+	strcpy(socket_path, "/tmp/tmate-slave-");
+	strcat(socket_path, token);
+}
+
+static char tmate_token_digits[] = "abcdefghijklmnopqrstuvwxyz"
+				   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+				   "0123456789";
+#define NUM_DIGITS (sizeof(tmate_token_digits) - 1)
+
+static char *get_random_token(void)
+{
+	int i;
+	char *token = xmalloc(TMATE_TOKEN_LEN + 1);
+
+	ssh_get_random(token, TMATE_TOKEN_LEN, 0);
+	for (i = 0; i < TMATE_TOKEN_LEN; i++)
+		token[i] = tmate_token_digits[token[i] % NUM_DIGITS];
+	token[i] = 0;
+
+	return token;
+}
+
+static int validate_token(const char *token)
+{
+	int len = strlen(token);
+	int i;
+
+	if (len != TMATE_TOKEN_LEN)
+		return -1;
+
+	for (i = 0; i < len; i++) {
+		if (!strchr(tmate_token_digits, token[i]))
+			return -1;
+	}
+
+	return 0;
+}
+
+static void tmate_spawn_slave_server(struct tmate_ssh_client *client)
+{
+	char *token;
 	struct tmate_encoder encoder;
 	struct tmate_decoder decoder;
 
-	tmate_debug("Spawn tmux slave server");
+	token = get_random_token();
+	set_session_token(token);
+	free(token);
 
-	ev_base = osdep_event_init();
+	tmate_debug("Spawning tmux slave server %s", tmate_session_token);
+
+	tmux_socket_fd = server_create_socket();
+	if (tmux_socket_fd < 0)
+		tmate_fatal("Cannot create to the tmux socket");
 
 	tmate_encoder_init(&encoder);
 	tmate_decoder_init(&decoder);
@@ -59,22 +111,68 @@ void tmate_spawn_slave_server(struct tmate_ssh_client *client)
 	/* never reached */
 }
 
-void tmate_spawn_slave_client(struct tmate_ssh_client *ssh_client)
+static void ssh_echo(struct tmate_ssh_client *ssh_client,
+		     const char *str)
+{
+	ssh_channel_write(ssh_client->channel, str, strlen(str));
+}
+
+#define BAD_TOKEN_ERROR_STR						\
+"  "								 "\r\n" \
+"  Dear guest,"							 "\r\n" \
+"  "								 "\r\n" \
+"  There isn't much I can do without a valid session token."	 "\r\n" \
+"  Feel free to reach out if you are having issues."		 "\r\n" \
+"  "								 "\r\n" \
+"  Thanks,"							 "\r\n" \
+"  Nico"							 "\r\n" \
+"  "								 "\r\n"
+
+#define EXPIRED_TOKEN_ERROR_STR						\
+"  "								 "\r\n" \
+"  Dear guest,"							 "\r\n" \
+"  "								 "\r\n" \
+"  The provided session token is invalid, or has expired."	 "\r\n" \
+"  Feel free to reach out if you are having issues."		 "\r\n" \
+"  "								 "\r\n" \
+"  Thanks,"							 "\r\n" \
+"  Nico"							 "\r\n" \
+"  "								 "\r\n"
+
+static void random_sleep(void)
+{
+	usleep(50000 + (rand() % 50000));
+}
+
+static void tmate_spawn_slave_client(struct tmate_ssh_client *ssh_client)
 {
 	struct tmate_ssh_client_pty _client;
 	struct tmate_ssh_client_pty *client = &_client;
+	char *argv[] = {(char *)"attach", NULL};
+	char *token = ssh_client->username;
 	int slave_pty;
 	int ret;
-	char *argv[] = {(char *)"attach", NULL};
+
+	if (validate_token(token) < 0) {
+		ssh_echo(ssh_client, BAD_TOKEN_ERROR_STR);
+		tmate_fatal("Bad token");
+	}
+
+	set_session_token(token);
+
+	tmate_debug("Spawn tmux slave client %s", tmate_session_token);
+
+	tmux_socket_fd = client_connect(socket_path, 0);
+	if (tmux_socket_fd < 0) {
+		random_sleep(); /* for timing attacks */
+		ssh_echo(ssh_client, EXPIRED_TOKEN_ERROR_STR);
+		tmate_fatal("Expired token");
+	}
 
 	client->session = ssh_client->session;
 	client->channel = ssh_client->channel;
 	client->winsize_pty = ssh_client->winsize_pty;
 
-	tmate_debug("Spawn tmux slave client");
-
-	ev_base = osdep_event_init();
-
 	if (openpty(&client->pty, &slave_pty, NULL, NULL, NULL) < 0)
 		tmate_fatal("Cannot allocate pty");
 
@@ -89,3 +187,13 @@ void tmate_spawn_slave_client(struct tmate_ssh_client *ssh_client)
 	tmate_flush_pty(client);
 	exit(ret);
 }
+
+void tmate_spawn_slave(struct tmate_ssh_client *client)
+{
+	ev_base = osdep_event_init();
+
+	if (client->role == TMATE_ROLE_SERVER)
+		tmate_spawn_slave_server(client);
+	else
+		tmate_spawn_slave_client(client);
+}

tmate-ssh-server.c

@@ -105,18 +105,19 @@ static int init_client_step(struct tmate_ssh_client *client,
 	if (ssh_message_type(msg) == SSH_REQUEST_CHANNEL &&
 	    ssh_message_subtype(msg) == SSH_CHANNEL_REQUEST_SUBSYSTEM &&
 	    !strcmp(ssh_message_channel_request_subsystem(msg), "tmate")) {
-		alarm(0);
-		ssh_message_channel_request_reply_success(msg);
-		tmate_spawn_slave_server(client);
-		/* never reached */
+		client->role = TMATE_ROLE_SERVER;
 	}
 
 	/* shell request (slave client) */
 	if (ssh_message_type(msg) == SSH_REQUEST_CHANNEL &&
 	    ssh_message_subtype(msg) == SSH_CHANNEL_REQUEST_SHELL) {
+		client->role = TMATE_ROLE_CLIENT;
+	}
+
+	if (client->role) {
 		alarm(0);
 		ssh_message_channel_request_reply_success(msg);
-		tmate_spawn_slave_client(client);
+		tmate_spawn_slave(client);
 		/* never reached */
 	}
 

tmate.h

@@ -60,10 +60,15 @@ extern void tmate_decoder_commit(struct tmate_decoder *decoder, size_t len);
 typedef struct ssh_session_struct* ssh_session;
 typedef struct ssh_channel_struct* ssh_channel;
 
+#define TMATE_ROLE_SERVER 1
+#define TMATE_ROLE_CLIENT 2
+
 struct tmate_ssh_client {
 	ssh_session session;
 	ssh_channel channel;
 
+	int role;
+
 	struct tmate_encoder *encoder;
 	struct tmate_decoder *decoder;
 
@@ -102,10 +107,12 @@ extern void tmate_ssh_server_main(int port);
 
 /* tmate-slave.c */
 
-extern struct tmate_encoder *tmate_encoder;
+#define TMATE_TOKEN_LEN 25
 
-extern void tmate_spawn_slave_server(struct tmate_ssh_client *client);
-extern void tmate_spawn_slave_client(struct tmate_ssh_client *client);
+extern struct tmate_encoder *tmate_encoder;
+extern int tmux_socket_fd;
+
+extern void tmate_spawn_slave(struct tmate_ssh_client *client);
 
 /* tmate-debug.c */
 extern void tmate_print_trace(void);