Exit gracefully if conf.intf does not exist

If the interface named in 'conf.intf' does not exist then there is a
segfault. The user is not notified of the problem.
So, print an error message informing the user and exit gracefully instead
of a segfault.

This has been reported in Ubuntu.

Signed-off-by: Sudip Mukherjee <[email protected]>

main.c

@@ -28,6 +28,7 @@
 #include <err.h>
 #include <sys/socket.h>
 #include <net/if.h>
+#include <ifaddrs.h>
 
 #include <uwifi/packet_sock.h>
 #include <uwifi/util.h>
@@ -570,6 +571,25 @@ static void generate_mon_ifname(char *const buf, const size_t buf_size)
 	}
 }
 
+static bool check_if_exists(const char *const interface)
+{
+	struct ifaddrs *ifaddr, *ifa;
+	bool found = false;
+
+	if (getifaddrs(&ifaddr) == -1) {
+		printf("can not check interface names, continuing\n");
+		return true;
+	}
+	for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+		if (strcmp(ifa->ifa_name, interface) == 0) {
+			found = true;
+			break;
+		}
+	}
+	freeifaddrs(ifaddr);
+	return found;
+}
+
 int main(int argc, char** argv)
 {
 	sigset_t workmask;
@@ -612,6 +632,10 @@ int main(int argc, char** argv)
 		conf.intf.sock = net_open_client_socket(conf.serveraddr, conf.port);
 		cc_list_head_init(&conf.intf.wlan_nodes);
 	} else {
+		if (!check_if_exists(conf.intf.ifname)) {
+			fprintf(stderr, "invalid interface name, please check configuration\n");
+			return(-EINVAL);
+		}
 		ifctrl_init();
 		ifctrl_iwget_interface_info(&conf.intf);