Index: head/sys/compat/linuxkpi/common/include/linux/string.h
===================================================================
--- head/sys/compat/linuxkpi/common/include/linux/string.h	(revision 363204)
+++ head/sys/compat/linuxkpi/common/include/linux/string.h	(revision 363205)
@@ -1,166 +1,170 @@
 /*-
  * Copyright (c) 2010 Isilon Systems, Inc.
  * Copyright (c) 2010 iX Systems, Inc.
  * Copyright (c) 2010 Panasas, Inc.
  * Copyright (c) 2013-2017 Mellanox Technologies, Ltd.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice unmodified, this list of conditions, and the following
  *    disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  * $FreeBSD$
  */
 #ifndef	_LINUX_STRING_H_
 #define	_LINUX_STRING_H_
 
 #include <sys/ctype.h>
 
 #include <linux/types.h>
 #include <linux/gfp.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/err.h>
 
 #include <sys/libkern.h>
 
 #define	strnicmp(...) strncasecmp(__VA_ARGS__)
 
 static inline int
 match_string(const char *const *table, int n, const char *key)
 {
 	int i;
 
 	for (i = 0; i != n && table[i] != NULL; i++) {
 		if (strcmp(table[i], key) == 0)
 			return (i);
 	}
 	return (-EINVAL);
 }
 
 static inline void *
 memdup_user(const void *ptr, size_t len)
 {
 	void *retval;
 	int error;
 
 	retval = malloc(len, M_KMALLOC, M_WAITOK);
 	error = linux_copyin(ptr, retval, len);
 	if (error != 0) {
 		free(retval, M_KMALLOC);
 		return (ERR_PTR(error));
 	}
 	return (retval);
 }
 
 static inline void *
 memdup_user_nul(const void *ptr, size_t len)
 {
 	char *retval;
 	int error;
 
 	retval = malloc(len + 1, M_KMALLOC, M_WAITOK);
 	error = linux_copyin(ptr, retval, len);
 	if (error != 0) {
 		free(retval, M_KMALLOC);
 		return (ERR_PTR(error));
 	}
 	retval[len] = '\0';
 	return (retval);
 }
 
 static inline void *
 kmemdup(const void *src, size_t len, gfp_t gfp)
 {
 	void *dst;
 
 	dst = kmalloc(len, gfp);
 	if (dst != NULL)
 		memcpy(dst, src, len);
 	return (dst);
 }
 
 static inline char *
 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)
 		memcpy(retval, string, len);
 	return (retval);
 }
 
 static inline char *
 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);
 	return (retval);
 }
 
 static inline const char *
 kstrdup_const(const char *src, gfp_t gfp)
 {
 	return (kmemdup(src, strlen(src) + 1, gfp));
 }
 
 static inline char *
 skip_spaces(const char *str)
 {
 	while (isspace(*str))
 		++str;
 	return (__DECONST(char *, str));
 }
 
 static inline void *
 memchr_inv(const void *start, int c, size_t length)
 {
 	const u8 *ptr;
 	const u8 *end;
 	u8 ch;
 
 	ch = c;
 	ptr = start;
 	end = ptr + length;
 
 	while (ptr != end) {
 		if (*ptr != ch)
 			return (__DECONST(void *, ptr));
 		ptr++;
 	}
 	return (NULL);
 }
 
 static inline size_t
 str_has_prefix(const char *str, const char *prefix)
 {
 	size_t len;
 
 	len = strlen(prefix);
 	return (strncmp(str, prefix, len) == 0 ? len : 0);
 }
 
 #endif					/* _LINUX_STRING_H_ */