4 files changed, 24 insertions, 10 deletions
diff --git a/src/config.c b/src/config.c
index 725c4e4..511d4e7 100644
--- a/src/config.c
+++ b/src/config.c
@@ -98,6 +98,18 @@ void fastd_config_method(fastd_peer_group_t *group, const char *name) {
 	*method = fastd_string_stack_dup(name);
 }
 
+bool fastd_config_ifname(fastd_peer_t *peer, const char *ifname) {
+	if (strchr(ifname, '/'))
+		return false;
+
+	char **name = peer ? &peer->ifname : &conf.ifname;
+
+	free(*name);
+	*name = fastd_strdup(ifname);
+
+	return true;
+}
+
 /** Handles the configuration of a cipher implementation */
 void fastd_config_cipher(const char *name, const char *impl) {
 	if (!fastd_cipher_config(name, impl))
@@ -533,11 +545,6 @@ void fastd_configure(int argc, char *const argv[]) {
 
 /** Performs some basic checks on the configuration */
 static void config_check_base(void) {
-	if (conf.ifname) {
-		if (strchr(conf.ifname, '/'))
-			exit_error("config error: invalid interface name");
-	}
-
 #ifndef USE_PACKET_MARK
 	if (conf.packet_mark)
 		exit_error("config error: setting a packet mark is not supported on this system");
diff --git a/src/config.h b/src/config.h
index b96247f..0d1bffc 100644
--- a/src/config.h
+++ b/src/config.h
@@ -47,6 +47,7 @@ struct fastd_parser_state {
 
 void fastd_config_protocol(const char *name);
 void fastd_config_method(fastd_peer_group_t *group, const char *name);
+bool fastd_config_ifname(fastd_peer_t *peer, const char *ifname);
 void fastd_config_cipher(const char *name, const char *impl);
 void fastd_config_mac(const char *name, const char *impl);
 void fastd_config_bind_address(const fastd_peer_address_t *address, const char *bindtodev, bool default_v4, bool default_v6);
diff --git a/src/config.y b/src/config.y
index 36b7368..fb2ceee 100644
--- a/src/config.y
+++ b/src/config.y
@@ -302,7 +302,12 @@ log_level:	TOK_FATAL	{ $$ = LL_FATAL; }
 	|	TOK_DEBUG2	{ $$ = LL_DEBUG2; }
 	;
 
-interface:	TOK_STRING	{ free(conf.ifname); conf.ifname = fastd_strdup($1->str); }
+interface:	TOK_STRING	{
+			if (!fastd_config_ifname(NULL, $1->str)) {
+				fastd_config_error(&@$, state, "invalid interface name");
+				YYERROR;
+			}
+		}
 	;
 
 bind:		bind_address maybe_bind_interface maybe_bind_default {
@@ -528,8 +533,10 @@ peer_key:	TOK_STRING {
 	;
 
 peer_interface:	TOK_STRING {
-			free(state->peer->ifname);
-			state->peer->ifname = fastd_strdup($1->str);
+			if (!fastd_config_ifname(state->peer, $1->str)) {
+				fastd_config_error(&@$, state, "invalid interface name");
+				YYERROR;
+			}
 		}
 	;
 
diff --git a/src/options.c b/src/options.c
index 44b097b..a84830b 100644
--- a/src/options.c
+++ b/src/options.c
@@ -228,8 +228,7 @@ static void option_mode(const char *arg) {
 
 /** Handles the --interface option */
 static void option_interface(const char *arg) {
-	free(conf.ifname);
-	conf.ifname = fastd_strdup(arg);
+	fastd_config_ifname(NULL, arg);
 }
 
 /** Handles the --mtu option */