ipc: linux: enforce IFNAMSIZ limit

libmnl doesn't check lengths, so do our own checking before copying the
interface name to the netlink buffer.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/ipc-linux.h

@@ -479,6 +479,12 @@ static int kernel_get_device(struct wgdevice **device, const char *iface)
 	struct nlmsghdr *nlh;
 	struct mnlg_socket *nlg;
 
+	/* libmnl doesn't check the buffer size, so enforce that before using. */
+	if (strlen(iface) >= IFNAMSIZ) {
+		errno = ENAMETOOLONG;
+		return -ENAMETOOLONG;
+	}
+
 try_again:
 	ret = 0;
 	*device = calloc(1, sizeof(**device));