[mirror_ubuntu-artful-kernel.git] / lib / strncpy_from_user.c

#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/kasan-checks.h>
#include <linux/thread_info.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 */
		unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);

		*(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;

		unsafe_get_user(c,src+res, 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.
	 */
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;
		long retval;

		kasan_check_write(dst, count);
		check_object_size(dst, count, false);
		user_access_begin();
		retval = do_strncpy_from_user(dst, src, count, max);
		user_access_end();
		return retval;
	}
	return -EFAULT;
}
EXPORT_SYMBOL(strncpy_from_user);
Commit	Line	Data
bf3c2d6d RV	1	#include <linux/compiler.h>
bf3c2d6d RV	2	#include <linux/export.h>
1771c6e1	3	#include <linux/kasan-checks.h>
bf90e56e	4	#include <linux/thread_info.h>
2922585b DM	5	#include <linux/uaccess.h>
	6	#include <linux/kernel.h>
	7	#include <linux/errno.h>
	8
	9	#include <asm/byteorder.h>
36126f8f	10	#include <asm/word-at-a-time.h>
2922585b DM	11
	12	#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
	13	#define IS_UNALIGNED(src, dst) 0
	14	#else
	15	#define IS_UNALIGNED(src, dst) \
	16	(((long) dst \| (long) src) & (sizeof(long) - 1))
	17	#endif
	18
	19	/*
	20	* Do a strncpy, return length of string without final '\0'.
	21	* 'count' is the user-supplied count (return 'count' if we
	22	* hit it), 'max' is the address space maximum (and we return
	23	* -EFAULT if we hit it).
	24	*/
	25	static inline long do_strncpy_from_user(char dst, const char __user src, long count, unsigned long max)
	26	{
36126f8f	27	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
2922585b DM	28	long res = 0;
	29
	30	/*
	31	* Truncate 'max' to the user-specified limit, so that
	32	* we only have one limit we need to check in the loop
	33	*/
	34	if (max > count)
	35	max = count;
	36
	37	if (IS_UNALIGNED(src, dst))
	38	goto byte_at_a_time;
	39
	40	while (max >= sizeof(unsigned long)) {
36126f8f	41	unsigned long c, data;
2922585b DM	42
2922585b DM	43	/* Fall back to byte-at-a-time if we get a page fault */
1bd4403d LT	44	unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
1bd4403d LT	45
2922585b	46	(unsigned long )(dst+res) = c;
36126f8f LT	47	if (has_zero(c, &data, &constants)) {
	48	data = prep_zero_mask(c, data, &constants);
	49	data = create_zero_mask(data);
	50	return res + find_zero(data);
2922585b DM	51	}
	52	res += sizeof(unsigned long);
	53	max -= sizeof(unsigned long);
	54	}
	55
	56	byte_at_a_time:
	57	while (max) {
	58	char c;
	59
1bd4403d	60	unsafe_get_user(c,src+res, efault);
2922585b DM	61	dst[res] = c;
	62	if (!c)
	63	return res;
	64	res++;
	65	max--;
	66	}
	67
	68	/*
	69	* Uhhuh. We hit 'max'. But was that the user-specified maximum
	70	* too? If so, that's ok - we got as much as the user asked for.
	71	*/
	72	if (res >= count)
	73	return res;
	74
	75	/*
	76	* Nope: we hit the address space limit, and we still had more
	77	* characters the caller would have wanted. That's an EFAULT.
	78	*/
1bd4403d	79	efault:
2922585b DM	80	return -EFAULT;
	81	}
	82
	83	/**
	84	* strncpy_from_user: - Copy a NUL terminated string from userspace.
	85	* @dst: Destination address, in kernel space. This buffer must be at
	86	* least @count bytes long.
	87	* @src: Source address, in user space.
	88	* @count: Maximum number of bytes to copy, including the trailing NUL.
	89	*
	90	* Copies a NUL-terminated string from userspace to kernel space.
	91	*
	92	* On success, returns the length of the string (not including the trailing
	93	* NUL).
	94	*
	95	* If access to userspace fails, returns -EFAULT (some data may have been
	96	* copied).
	97	*
	98	* If @count is smaller than the length of the string, copies @count bytes
	99	* and returns @count.
	100	*/
	101	long strncpy_from_user(char dst, const char __user src, long count)
	102	{
	103	unsigned long max_addr, src_addr;
	104
	105	if (unlikely(count <= 0))
	106	return 0;
	107
	108	max_addr = user_addr_max();
	109	src_addr = (unsigned long)src;
	110	if (likely(src_addr < max_addr)) {
	111	unsigned long max = max_addr - src_addr;
9fd4470f LT	112	long retval;
9fd4470f LT	113
1771c6e1	114	kasan_check_write(dst, count);
bf90e56e	115	check_object_size(dst, count, false);
9fd4470f LT	116	user_access_begin();
	117	retval = do_strncpy_from_user(dst, src, count, max);
	118	user_access_end();
	119	return retval;
2922585b DM	120	}
	121	return -EFAULT;
	122	}
	123	EXPORT_SYMBOL(strncpy_from_user);