Commit 96840aa0 authored by Davi Arnaut's avatar Davi Arnaut Committed by Linus Torvalds
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[PATCH] strndup_user()

This patch series creates a strndup_user() function to easy copying C strings
from userspace.  Also we avoid common pitfalls like userspace modifying the
final \0 after the strlen_user().
Signed-off-by: default avatarDavi Arnaut <>
Cc: David Howells <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 6687a97d
......@@ -18,6 +18,8 @@ extern char * strsep(char **,const char *);
extern __kernel_size_t strspn(const char *,const char *);
extern __kernel_size_t strcspn(const char *,const char *);
extern char *strndup_user(const char __user *, long);
* Include machine specific inline routines
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/module.h>
#include <linux/err.h>
#include <asm/uaccess.h>
* kzalloc - allocate memory. The memory is set to zero.
......@@ -37,3 +39,38 @@ char *kstrdup(const char *s, gfp_t gfp)
return buf;
* strndup_user - duplicate an existing string from user space
* @s: The string to duplicate
* @n: Maximum number of bytes to copy, including the trailing NUL.
char *strndup_user(const char __user *s, long n)
char *p;
long length;
length = strnlen_user(s, n);
if (!length)
return ERR_PTR(-EFAULT);
if (length > n)
return ERR_PTR(-EINVAL);
p = kmalloc(length, GFP_KERNEL);
if (!p)
return ERR_PTR(-ENOMEM);
if (copy_from_user(p, s, length)) {
return ERR_PTR(-EFAULT);
p[length - 1] = '\0';
return p;
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