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