diff --git a/sys/compat/linuxkpi/common/include/linux/string.h b/sys/compat/linuxkpi/common/include/linux/string.h
--- a/sys/compat/linuxkpi/common/include/linux/string.h
+++ b/sys/compat/linuxkpi/common/include/linux/string.h
@@ -98,6 +98,15 @@
 	return (dst);
 }
 
+static inline char *
+strndup_user(const char __user *ustr, long n)
+{
+	if (n < 1)
+		return (ERR_PTR(-EINVAL));
+
+	return (memdup_user_nul(ustr, n - 1));
+}
+
 static inline char *
 kstrdup(const char *string, gfp_t gfp)
 {