Index: uspace/srv/fs/exfat/exfat_dentry.c
===================================================================
--- uspace/srv/fs/exfat/exfat_dentry.c	(revision ff0c270eaae7fb0bcea1e0d39986792efa5d9d5b)
+++ uspace/srv/fs/exfat/exfat_dentry.c	(revision 9fe4db3f6a27e5011cbcd44c201417d304469e1c)
@@ -101,11 +101,30 @@
 bool exfat_valid_char(wchar_t ch)
 {
-	/* TODO */
-	return true;
+	switch (ch) {
+	case 0x01 ... 0x1F:
+	case '/':
+	case '\\':
+	case '?':
+	case '|':
+	case '>':
+	case '<':
+	case '"':
+	case '*':
+	case ':':
+		return false;
+	default:
+		return true;
+	}
 }
 
 bool exfat_valid_name(const char *name)
 {
-	/* TODO */
+	size_t off = 0;
+	wchar_t ch;
+
+	while ((ch = str_decode(name, &off, STR_NO_LIMIT)) != 0) {
+		if (!exfat_valid_char(ch))
+			return false;
+	}
 	return true;
 }