Minor tweaks and improvements to the tunala demo.

- Add "-cipher" and "-out_state" command line arguments to control SSL
  cipher-suites and handshake debug output respectively.

- Implemented error handling for SSL handshakes that break down. This uses
  a cheat - storing a non-NULL pointer as "app_data" in the SSL structure
  when the SSL should be killed.

demos/tunala/Makefile

@@ -17,8 +17,8 @@ COMPILE=$(CC) $(CFLAGS) -c
 # Edit, particularly the "-ldl" if not building with "dlfcn" support
 LINK_FLAGS=-L$(SSL_LIBDIR) -lssl -lcrypto -ldl
 
-SRCS=buffer.c ip.c sm.c tunala.c
-OBJS=buffer.o ip.o sm.o tunala.o
+SRCS=buffer.c cb.c ip.c sm.c tunala.c
+OBJS=buffer.o cb.o ip.o sm.o tunala.o
 
 TARGETS=tunala
 
@@ -35,6 +35,7 @@ tunala: $(OBJS)
 
 # Extra dependencies, should really use makedepend
 buffer.o: buffer.c tunala.h
+cb.o: cb.c tunala.h
 ip.o: ip.c tunala.h
 sm.o: sm.c tunala.h
 tunala.o: tunala.c tunala.h

demos/tunala/buffer.c

@@ -101,6 +101,37 @@ int buffer_to_fd(buffer_t *buf, int fd)
 
 #ifndef NO_OPENSSL
 
+static void int_ssl_check(SSL *s, int ret)
+{
+	int e = SSL_get_error(s, ret);
+	switch(e) {
+		/* These seem to be harmless and already "dealt with" by our
+		 * non-blocking environment. NB: "ZERO_RETURN" is the clean
+		 * "error" indicating a successfully closed SSL tunnel. We let
+		 * this happen because our IO loop should not appear to have
+		 * broken on this condition - and outside the IO loop, the
+		 * "shutdown" state is checked. */
+	case SSL_ERROR_NONE:
+	case SSL_ERROR_WANT_READ:
+	case SSL_ERROR_WANT_WRITE:
+	case SSL_ERROR_WANT_X509_LOOKUP:
+	case SSL_ERROR_ZERO_RETURN:
+		return;
+		/* These seem to be indications of a genuine error that should
+		 * result in the SSL tunnel being regarded as "dead". */
+	case SSL_ERROR_SYSCALL:
+	case SSL_ERROR_SSL:
+		SSL_set_app_data(s, (char *)1);
+		return;
+	default:
+		break;
+	}
+	/* For any other errors that (a) exist, and (b) crop up - we need to
+	 * interpret what to do with them - so "politely inform" the caller that
+	 * the code needs updating here. */
+	abort();
+}
+
 void buffer_from_SSL(buffer_t *buf, SSL *ssl)
 {
 	int ret;
@@ -109,6 +140,8 @@ void buffer_from_SSL(buffer_t *buf, SSL *ssl)
 	ret = SSL_read(ssl, buf->data + buf->used, buffer_unused(buf));
 	if(ret > 0)
 		buf->used += ret;
+	if(ret < 0)
+		int_ssl_check(ssl, ret);
 }
 
 void buffer_to_SSL(buffer_t *buf, SSL *ssl)
@@ -119,6 +152,8 @@ void buffer_to_SSL(buffer_t *buf, SSL *ssl)
 	ret = SSL_write(ssl, buf->data, buf->used);
 	if(ret > 0)
 		buffer_takedata(buf, NULL, ret);
+	if(ret < 0)
+		int_ssl_check(ssl, ret);
 }
 
 void buffer_from_BIO(buffer_t *buf, BIO *bio)

demos/tunala/cb.c

+#include "tunala.h"
+
+#ifndef NO_OPENSSL
+
+/* For callbacks generating output, here are their file-descriptors. */
+static FILE *fp_cb_ssl_info = NULL;
+
+/* This function is largely borrowed from the one used in OpenSSL's "s_client"
+ * and "s_server" utilities. */
+void cb_ssl_info(SSL *s, int where, int ret)
+{
+	char *str1, *str2;
+	int w;
+
+	if(!fp_cb_ssl_info)
+		return;
+
+	w = where & ~SSL_ST_MASK;
+	str1 = (w & SSL_ST_CONNECT ? "SSL_connect" : (w & SSL_ST_ACCEPT ?
+				"SSL_accept" : "undefined")),
+	str2 = SSL_state_string_long(s);
+
+	if (where & SSL_CB_LOOP)
+		fprintf(stderr, "%s:%s\n", str1, str2);
+	else if (where & SSL_CB_EXIT) {
+		if (ret == 0)
+			fprintf(stderr, "%s:failed in %s\n", str1, str2);
+		else if (ret < 0)
+			fprintf(stderr, "%s:error in %s\n", str1, str2);
+	}
+}
+
+void cb_ssl_info_set_output(FILE *fp)
+{
+	fp_cb_ssl_info = fp;
+}
+
+#endif /* !defined(NO_OPENSSL) */
+

demos/tunala/sm.c

@@ -55,7 +55,7 @@ SSL *state_machine_get_SSL(state_machine_t *machine)
 	return machine->ssl;
 }
 
-void state_machine_set_SSL(state_machine_t *machine, SSL *ssl, int is_server)
+int state_machine_set_SSL(state_machine_t *machine, SSL *ssl, int is_server)
 {
 	if(machine->ssl)
 		/* Shouldn't ever be set twice */
@@ -75,7 +75,7 @@ void state_machine_set_SSL(state_machine_t *machine, SSL *ssl, int is_server)
 	/* If we're the first one to generate traffic - do it now otherwise we
 	 * go into the next select empty-handed and our peer will not send data
 	 * but will similarly wait for us. */
-	state_machine_churn(machine);
+	return state_machine_churn(machine);
 }
 
 /* Performs the data-IO loop and returns zero if the machine should close */
@@ -98,13 +98,14 @@ int state_machine_churn(state_machine_t *machine)
 			/* Still buffered data on the clean side to go out */
 			return 1;
 	}
-	if(SSL_get_shutdown(machine->ssl)) {
-		/* An SSL shutdown was underway */
-		if(buffer_empty(&machine->dirty_out)) {
-			/* Great, we can seal off the dirty side completely */
-			if(!state_machine_close_dirty(machine))
-				return 0;
-		}
+	/* We close on the SSL side if the info callback noticed some problems
+	 * or an SSL shutdown was underway and shutdown traffic had all been
+	 * sent. */
+	if(SSL_get_app_data(machine->ssl) || (SSL_get_shutdown(machine->ssl) &&
+				buffer_empty(&machine->dirty_out))) {
+		/* Great, we can seal off the dirty side completely */
+		if(!state_machine_close_dirty(machine))
+			return 0;
 	}
 	/* Either the SSL is alive and well, or the closing process still has
 	 * outgoing data waiting to be sent */

demos/tunala/tunala.c

@@ -67,7 +67,8 @@ typedef struct _tunala_world_t {
 /*****************************/
 
 static SSL_CTX *initialise_ssl_ctx(int server_mode, const char *engine_id,
-		const char *CAfile, const char *cert, const char *key);
+		const char *CAfile, const char *cert, const char *key,
+		const char *cipher_list, int out_state);
 static void selector_init(tunala_selector_t *selector);
 static void selector_add_listener(tunala_selector_t *selector, int fd);
 static void selector_add_tunala(tunala_selector_t *selector, tunala_item_t *t);
@@ -92,6 +93,8 @@ static const char *def_cert = NULL;
 static const char *def_key = NULL;
 static const char *def_engine_id = NULL;
 static int def_server_mode = 0;
+static const char *def_cipher_list = NULL;
+static int def_out_state = 0;
 
 static const char *helpstring =
 	"\n'Tunala' (A tunneler with a New Zealand accent)\n"
@@ -104,6 +107,8 @@ static const char *helpstring =
 	"    -key <path|NULL>       (default = whatever '-cert' is)\n"
 	"    -engine <id|NULL>      (default = NULL)\n"
 	"    -server <0|1>          (default = 0, ie. an SSL client)\n"
+	"    -cipher <list>         (specifies cipher list to use)\n"
+	"    -out_state             (prints SSL handshake states)\n"
 	"    -<h|help|?>            (displays this help screen)\n"
 	"NB: It is recommended to specify a cert+key when operating as an\n"
 	"SSL server. If you only specify '-cert', the same file must\n"
@@ -178,6 +183,8 @@ int main(int argc, char *argv[])
 	const char *key = def_key;
 	const char *engine_id = def_engine_id;
 	int server_mode = def_server_mode;
+	const char *cipher_list = def_cipher_list;
+	int out_state = def_out_state;
 
 /* Parse command-line arguments */
 next_arg:
@@ -242,6 +249,15 @@ next_arg:
 			if(!parse_server_mode(*argv, &server_mode))
 				return 1;
 			goto next_arg;
+		} else if(strcmp(*argv, "-cipher") == 0) {
+			if(argc < 2)
+				return usage("-cipher requires an argument", 0);
+			argc--; argv++;
+			cipher_list = *argv;
+			goto next_arg;
+		} else if(strcmp(*argv, "-out_state") == 0) {
+			out_state = 1;
+			goto next_arg;
 		} else if((strcmp(*argv, "-h") == 0) ||
 				(strcmp(*argv, "-help") == 0) ||
 				(strcmp(*argv, "-?") == 0)) {
@@ -257,7 +273,7 @@ next_arg:
 	err_str0("ip_initialise succeeded");
 	/* Create the SSL_CTX */
 	if((world.ssl_ctx = initialise_ssl_ctx(server_mode, engine_id,
-			cacert, cert, key)) == NULL)
+			cacert, cert, key, cipher_list, out_state)) == NULL)
 		return err_str1("initialise_ssl_ctx(engine_id=%s) failed",
 			(engine_id == NULL) ? "NULL" : engine_id);
 	err_str1("initialise_ssl_ctx(engine_id=%s) succeeded",
@@ -306,12 +322,11 @@ main_loop:
 					&newfd) == 1)) {
 		/* We have a new connection */
 		if(!tunala_world_new_item(&world, newfd,
-					proxy_ip, proxy_port)) {
+					proxy_ip, proxy_port))
 			fprintf(stderr, "tunala_world_new_item failed\n");
-			abort();
-		}
-		fprintf(stderr, "Info, new tunnel opened, now up to %d\n",
-				world.tunnels_used);
+		else
+			fprintf(stderr, "Info, new tunnel opened, now up to "
+					"%d\n", world.tunnels_used);
 	}
 	/* Give each tunnel its moment, note the while loop is because it makes
 	 * the logic easier than with "for" to deal with an array that may shift
@@ -344,7 +359,8 @@ main_loop:
 /****************/
 
 static SSL_CTX *initialise_ssl_ctx(int server_mode, const char *engine_id,
-		const char *CAfile, const char *cert, const char *key)
+		const char *CAfile, const char *cert, const char *key,
+		const char *cipher_list, int out_state)
 {
 	SSL_CTX *ctx, *ret = NULL;
 	SSL_METHOD *meth;
@@ -439,6 +455,23 @@ static SSL_CTX *initialise_ssl_ctx(int server_mode, const char *engine_id,
 	} else
 		fprintf(stderr, "Info, operating without a cert or key\n");
 
+	/* cipher_list */
+	if(cipher_list) {
+		if(!SSL_CTX_set_cipher_list(ctx, cipher_list)) {
+			fprintf(stderr, "Error setting cipher list '%s'\n",
+					cipher_list);
+			goto err;
+		}
+		fprintf(stderr, "Info, set cipher list '%s'\n", cipher_list);
+	} else
+		fprintf(stderr, "Info, operating with default cipher list\n");
+
+	/* out_state (output of SSL handshake states to screen). */
+	if(out_state) {
+		SSL_CTX_set_info_callback(ctx, cb_ssl_info);
+		cb_ssl_info_set_output(stderr);
+	}
+
 	/* Success! */
 	ret = ctx;
 err:
@@ -577,9 +610,15 @@ static int tunala_world_new_item(tunala_world_t *world, int fd,
 {
 	tunala_item_t *item;
 	int newfd;
+	SSL *new_ssl = NULL;
 
 	if(!tunala_world_make_room(world))
 		return 0;
+	if((new_ssl = SSL_new(world->ssl_ctx)) == NULL) {
+		fprintf(stderr, "Error creating new SSL\n");
+		ERR_print_errors_fp(stderr);
+		return 0;
+	}
 	item = world->tunnels + (world->tunnels_used++);
 	state_machine_init(&item->sm);
 	item->clean_read = item->clean_send =
@@ -596,11 +635,13 @@ static int tunala_world_new_item(tunala_world_t *world, int fd,
 		item->clean_read = item->clean_send = fd;
 		item->dirty_read = item->dirty_send = newfd;
 	}
-	state_machine_set_SSL(&item->sm, SSL_new(world->ssl_ctx),
-			world->server_mode);
+	/* We use the SSL's "app_data" to indicate a call-back induced "kill" */
+	SSL_set_app_data(new_ssl, NULL);
+	if(!state_machine_set_SSL(&item->sm, new_ssl, world->server_mode))
+		goto err;
 	return 1;
 err:
-	state_machine_close(&item->sm);
+	tunala_world_del_item(world, world->tunnels_used - 1);
 	return 0;
 
 }

demos/tunala/tunala.h

@@ -89,6 +89,10 @@ void buffer_from_SSL(buffer_t *buf, SSL *ssl);
 void buffer_to_SSL(buffer_t *buf, SSL *ssl);
 void buffer_from_BIO(buffer_t *buf, BIO *bio);
 void buffer_to_BIO(buffer_t *buf, BIO *bio);
+
+/* Callbacks */
+void cb_ssl_info(SSL *s, int where, int ret);
+void cb_ssl_info_set_output(FILE *fp); /* Called if output should be sent too */
 #endif /* !defined(NO_OPENSSL) */
 #endif /* !defined(NO_BUFFER) */
 
@@ -111,7 +115,7 @@ void state_machine_init(state_machine_t *machine);
 void state_machine_close(state_machine_t *machine);
 buffer_t *state_machine_get_buffer(state_machine_t *machine, sm_buffer_t type);
 SSL *state_machine_get_SSL(state_machine_t *machine);
-void state_machine_set_SSL(state_machine_t *machine, SSL *ssl, int is_server);
+int state_machine_set_SSL(state_machine_t *machine, SSL *ssl, int is_server);
 /* Performs the data-IO loop and returns zero if the machine should close */
 int state_machine_churn(state_machine_t *machine);
 /* Is used to handle closing conditions - namely when one side of the tunnel has