linux/mm/util.c
Alexey Dobriyan 1a2f67b459 [PATCH] kmemdup: introduce
One of idiomatic ways to duplicate a region of memory is

	dst = kmalloc(len, GFP_KERNEL);
	if (!dst)
		return -ENOMEM;
	memcpy(dst, src, len);

which is neat code except a programmer needs to write size twice.  Which
sometimes leads to mistakes.  If len passed to kmalloc is smaller that len
passed to memcpy, it's straight overwrite-beyond-end.  If len passed to
memcpy is smaller than len passed to kmalloc, it's either a) legit
behaviour ;-), or b) cloned buffer will contain garbage in second half.

Slight trolling of commit lists shows several duplications bugs
done exactly because of diverged lenghts:

	Linux:
		[CRYPTO]: Fix memcpy/memset args.
		[PATCH] memcpy/memset fixes
	OpenBSD:
		kerberosV/src/lib/asn1: der_copy.c:1.4

If programmer is given only one place to play with lengths, I believe, such
mistakes could be avoided.

With kmemdup, the snippet above will be rewritten as:

	dst = kmemdup(src, len, GFP_KERNEL);
	if (!dst)
		return -ENOMEM;

This also leads to smaller code (kzalloc effect). Quick grep shows
200+ places where kmemdup() can be used.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-01 00:39:19 -07:00

95 lines
1.7 KiB
C

#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.
* @size: how many bytes of memory are required.
* @flags: the type of memory to allocate.
*/
void *__kzalloc(size_t size, gfp_t flags)
{
void *ret = ____kmalloc(size, flags);
if (ret)
memset(ret, 0, size);
return ret;
}
EXPORT_SYMBOL(__kzalloc);
/*
* kstrdup - allocate space for and copy an existing string
*
* @s: the string to duplicate
* @gfp: the GFP mask used in the kmalloc() call when allocating memory
*/
char *kstrdup(const char *s, gfp_t gfp)
{
size_t len;
char *buf;
if (!s)
return NULL;
len = strlen(s) + 1;
buf = ____kmalloc(len, gfp);
if (buf)
memcpy(buf, s, len);
return buf;
}
EXPORT_SYMBOL(kstrdup);
/**
* kmemdup - duplicate region of memory
*
* @src: memory region to duplicate
* @len: memory region length
* @gfp: GFP mask to use
*/
void *kmemdup(const void *src, size_t len, gfp_t gfp)
{
void *p;
p = ____kmalloc(len, gfp);
if (p)
memcpy(p, src, len);
return p;
}
EXPORT_SYMBOL(kmemdup);
/*
* 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)) {
kfree(p);
return ERR_PTR(-EFAULT);
}
p[length - 1] = '\0';
return p;
}
EXPORT_SYMBOL(strndup_user);