1#include <linux/kernel.h>
2#include <linux/export.h>
3#include <linux/uaccess.h>
4
5#include <asm/word-at-a-time.h>
6
7/* Set bits in the first 'n' bytes when loaded from memory */
8#ifdef __LITTLE_ENDIAN
9#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
10#else
11#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
12#endif
13
14/*
15 * Do a strnlen, return length of string *with* final '\0'.
16 * 'count' is the user-supplied count, while 'max' is the
17 * address space maximum.
18 *
19 * Return 0 for exceptions (which includes hitting the address
20 * space maximum), or 'count+1' if hitting the user-supplied
21 * maximum count.
22 *
23 * NOTE! We can sometimes overshoot the user-supplied maximum
24 * if it fits in a aligned 'long'. The caller needs to check
25 * the return value against "> max".
26 */
27static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
28{
29	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
30	long align, res = 0;
31	unsigned long c;
32
33	/*
34	 * Truncate 'max' to the user-specified limit, so that
35	 * we only have one limit we need to check in the loop
36	 */
37	if (max > count)
38		max = count;
39
40	/*
41	 * Do everything aligned. But that means that we
42	 * need to also expand the maximum..
43	 */
44	align = (sizeof(long) - 1) & (unsigned long)src;
45	src -= align;
46	max += align;
47
48	if (unlikely(__get_user(c,(unsigned long __user *)src)))
49		return 0;
50	c |= aligned_byte_mask(align);
51
52	for (;;) {
53		unsigned long data;
54		if (has_zero(c, &data, &constants)) {
55			data = prep_zero_mask(c, data, &constants);
56			data = create_zero_mask(data);
57			return res + find_zero(data) + 1 - align;
58		}
59		res += sizeof(unsigned long);
60		/* We already handled 'unsigned long' bytes. Did we do it all ? */
61		if (unlikely(max <= sizeof(unsigned long)))
62			break;
63		max -= sizeof(unsigned long);
64		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
65			return 0;
66	}
67	res -= align;
68
69	/*
70	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
71	 * too? If so, return the marker for "too long".
72	 */
73	if (res >= count)
74		return count+1;
75
76	/*
77	 * Nope: we hit the address space limit, and we still had more
78	 * characters the caller would have wanted. That's 0.
79	 */
80	return 0;
81}
82
83/**
84 * strnlen_user: - Get the size of a user string INCLUDING final NUL.
85 * @str: The string to measure.
86 * @count: Maximum count (including NUL character)
87 *
88 * Context: User context only.  This function may sleep.
89 *
90 * Get the size of a NUL-terminated string in user space.
91 *
92 * Returns the size of the string INCLUDING the terminating NUL.
93 * If the string is too long, returns a number larger than @count. User
94 * has to check the return value against "> count".
95 * On exception (or invalid count), returns 0.
96 *
97 * NOTE! You should basically never use this function. There is
98 * almost never any valid case for using the length of a user space
99 * string, since the string can be changed at any time by other
100 * threads. Use "strncpy_from_user()" instead to get a stable copy
101 * of the string.
102 */
103long strnlen_user(const char __user *str, long count)
104{
105	unsigned long max_addr, src_addr;
106
107	if (unlikely(count <= 0))
108		return 0;
109
110	max_addr = user_addr_max();
111	src_addr = (unsigned long)str;
112	if (likely(src_addr < max_addr)) {
113		unsigned long max = max_addr - src_addr;
114		return do_strnlen_user(str, count, max);
115	}
116	return 0;
117}
118EXPORT_SYMBOL(strnlen_user);
119
120/**
121 * strlen_user: - Get the size of a user string INCLUDING final NUL.
122 * @str: The string to measure.
123 *
124 * Context: User context only.  This function may sleep.
125 *
126 * Get the size of a NUL-terminated string in user space.
127 *
128 * Returns the size of the string INCLUDING the terminating NUL.
129 * On exception, returns 0.
130 *
131 * If there is a limit on the length of a valid string, you may wish to
132 * consider using strnlen_user() instead.
133 */
134long strlen_user(const char __user *str)
135{
136	unsigned long max_addr, src_addr;
137
138	max_addr = user_addr_max();
139	src_addr = (unsigned long)str;
140	if (likely(src_addr < max_addr)) {
141		unsigned long max = max_addr - src_addr;
142		return do_strnlen_user(str, ~0ul, max);
143	}
144	return 0;
145}
146EXPORT_SYMBOL(strlen_user);
147