[linux.git] / lib / strncpy_from_user.c

#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/errno.h>

#include <asm/byteorder.h>
#include <asm/word-at-a-time.h>

#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
#define IS_UNALIGNED(src, dst)	0
#else
#define IS_UNALIGNED(src, dst)	\
	(((long) dst | (long) src) & (sizeof(long) - 1))
#endif

/*
 * Do a strncpy, return length of string without final '\0'.
 * 'count' is the user-supplied count (return 'count' if we
 * hit it), 'max' is the address space maximum (and we return
 * -EFAULT if we hit it).
 */
static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
{
	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
	long res = 0;

	/*
	 * Truncate 'max' to the user-specified limit, so that
	 * we only have one limit we need to check in the loop
	 */
	if (max > count)
		max = count;

	if (IS_UNALIGNED(src, dst))
		goto byte_at_a_time;

	while (max >= sizeof(unsigned long)) {
		unsigned long c, data;

		/* Fall back to byte-at-a-time if we get a page fault */
		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
			break;
		*(unsigned long *)(dst+res) = c;
		if (has_zero(c, &data, &constants)) {
			data = prep_zero_mask(c, data, &constants);
			data = create_zero_mask(data);
			return res + find_zero(data);
		}
		res += sizeof(unsigned long);
		max -= sizeof(unsigned long);
	}

byte_at_a_time:
	while (max) {
		char c;

		if (unlikely(__get_user(c,src+res)))
			return -EFAULT;
		dst[res] = c;
		if (!c)
			return res;
		res++;
		max--;
	}

	/*
	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
	 * too? If so, that's ok - we got as much as the user asked for.
	 */
	if (res >= count)
		return res;

	/*
	 * Nope: we hit the address space limit, and we still had more
	 * characters the caller would have wanted. That's an EFAULT.
	 */
	return -EFAULT;
}

/**
 * strncpy_from_user: - Copy a NUL terminated string from userspace.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @src:   Source address, in user space.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from userspace to kernel space.
 *
 * On success, returns the length of the string (not including the trailing
 * NUL).
 *
 * If access to userspace fails, returns -EFAULT (some data may have been
 * copied).
 *
 * If @count is smaller than the length of the string, copies @count bytes
 * and returns @count.
 */
long strncpy_from_user(char *dst, const char __user *src, long count)
{
	unsigned long max_addr, src_addr;

	if (unlikely(count <= 0))
		return 0;

	max_addr = user_addr_max();
	src_addr = (unsigned long)src;
	if (likely(src_addr < max_addr)) {
		unsigned long max = max_addr - src_addr;
		return do_strncpy_from_user(dst, src, count, max);
	}
	return -EFAULT;
}
EXPORT_SYMBOL(strncpy_from_user);
Commit	Line	Data
2922585b DM	1	#include <linux/module.h>
	2	#include <linux/uaccess.h>
	3	#include <linux/kernel.h>
	4	#include <linux/errno.h>
	5
	6	#include <asm/byteorder.h>
36126f8f	7	#include <asm/word-at-a-time.h>
2922585b DM	8
	9	#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
	10	#define IS_UNALIGNED(src, dst) 0
	11	#else
	12	#define IS_UNALIGNED(src, dst) \
	13	(((long) dst \| (long) src) & (sizeof(long) - 1))
	14	#endif
	15
	16	/*
	17	* Do a strncpy, return length of string without final '\0'.
	18	* 'count' is the user-supplied count (return 'count' if we
	19	* hit it), 'max' is the address space maximum (and we return
	20	* -EFAULT if we hit it).
	21	*/
	22	static inline long do_strncpy_from_user(char dst, const char __user src, long count, unsigned long max)
	23	{
36126f8f	24	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
2922585b DM	25	long res = 0;
	26
	27	/*
	28	* Truncate 'max' to the user-specified limit, so that
	29	* we only have one limit we need to check in the loop
	30	*/
	31	if (max > count)
	32	max = count;
	33
	34	if (IS_UNALIGNED(src, dst))
	35	goto byte_at_a_time;
	36
	37	while (max >= sizeof(unsigned long)) {
36126f8f	38	unsigned long c, data;
2922585b DM	39
	40	/* Fall back to byte-at-a-time if we get a page fault */
	41	if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
	42	break;
2922585b	43	(unsigned long )(dst+res) = c;
36126f8f LT	44	if (has_zero(c, &data, &constants)) {
	45	data = prep_zero_mask(c, data, &constants);
	46	data = create_zero_mask(data);
	47	return res + find_zero(data);
2922585b DM	48	}
	49	res += sizeof(unsigned long);
	50	max -= sizeof(unsigned long);
	51	}
	52
	53	byte_at_a_time:
	54	while (max) {
	55	char c;
	56
	57	if (unlikely(__get_user(c,src+res)))
	58	return -EFAULT;
	59	dst[res] = c;
	60	if (!c)
	61	return res;
	62	res++;
	63	max--;
	64	}
	65
	66	/*
	67	* Uhhuh. We hit 'max'. But was that the user-specified maximum
	68	* too? If so, that's ok - we got as much as the user asked for.
	69	*/
	70	if (res >= count)
	71	return res;
	72
	73	/*
	74	* Nope: we hit the address space limit, and we still had more
	75	* characters the caller would have wanted. That's an EFAULT.
	76	*/
	77	return -EFAULT;
	78	}
	79
	80	/**
	81	* strncpy_from_user: - Copy a NUL terminated string from userspace.
	82	* @dst: Destination address, in kernel space. This buffer must be at
	83	* least @count bytes long.
	84	* @src: Source address, in user space.
	85	* @count: Maximum number of bytes to copy, including the trailing NUL.
	86	*
	87	* Copies a NUL-terminated string from userspace to kernel space.
	88	*
	89	* On success, returns the length of the string (not including the trailing
	90	* NUL).
	91	*
	92	* If access to userspace fails, returns -EFAULT (some data may have been
	93	* copied).
	94	*
	95	* If @count is smaller than the length of the string, copies @count bytes
	96	* and returns @count.
	97	*/
	98	long strncpy_from_user(char dst, const char __user src, long count)
	99	{
	100	unsigned long max_addr, src_addr;
	101
	102	if (unlikely(count <= 0))
	103	return 0;
	104
	105	max_addr = user_addr_max();
	106	src_addr = (unsigned long)src;
	107	if (likely(src_addr < max_addr)) {
	108	unsigned long max = max_addr - src_addr;
	109	return do_strncpy_from_user(dst, src, count, max);
	110	}
	111	return -EFAULT;
112	}
113	EXPORT_SYMBOL(strncpy_from_user);