From 34c2f79d835569e758b3d448e672a2ca81541f0a Mon Sep 17 00:00:00 2001
From: Vladimir Kondratyev <wulf@FreeBSD.org>
Date: Tue, 14 Jul 2020 21:56:59 +0000
Subject: [PATCH] linuxkpi: Ignore NULL pointers passed to string parameter of
 kstr(n)dup

That follows Linux and fixes related drm-kmod-5.3 panic.

Reviewed by:	imp, hselasky
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D25657
---
 sys/compat/linuxkpi/common/include/linux/string.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sys/compat/linuxkpi/common/include/linux/string.h b/sys/compat/linuxkpi/common/include/linux/string.h
index d8d509778adb..39201e203162 100644
--- a/sys/compat/linuxkpi/common/include/linux/string.h
+++ b/sys/compat/linuxkpi/common/include/linux/string.h
@@ -103,6 +103,8 @@ kstrdup(const char *string, gfp_t gfp)
 	char *retval;
 	size_t len;
 
+	if (string == NULL)
+		return (NULL);
 	len = strlen(string) + 1;
 	retval = kmalloc(len, gfp);
 	if (retval != NULL)
@@ -115,6 +117,8 @@ kstrndup(const char *string, size_t len, gfp_t gfp)
 {
 	char *retval;
 
+	if (string == NULL)
+		return (NULL);
 	retval = kmalloc(len + 1, gfp);
 	if (retval != NULL)
 		strncpy(retval, string, len);