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 +98,23 @@
 	return (dst);
 }
 
+static inline char *
+strndup_user(const char __user *ustr, long n)
+{
+	char *kstr;
+
+	if (n < 1)
+		return (ERR_PTR(-EINVAL));
+
+	kstr = memdup_user(ustr, n);
+	if (IS_ERR(kstr))
+		return (kstr);
+
+	kstr[n-1] = '\0';
+
+	return (kstr);
+}
+
 static inline char *
 kstrdup(const char *string, gfp_t gfp)
 {