1
2#include <linux/kernel.h>
3#include <linux/export.h>
4#include <linux/uaccess.h>
5
6#include <asm/word-at-a-time.h>
7
8
9#ifdef __LITTLE_ENDIAN
10# define aligned_byte_mask(n) ((1ul << 8*(n))-1)
11#else
12# define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
13#endif
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28static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
29{
30 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
31 long align, res = 0;
32 unsigned long c;
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36
37
38 if (max > count)
39 max = count;
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44
45 align = (sizeof(long) - 1) & (unsigned long)src;
46 src -= align;
47 max += align;
48
49 unsafe_get_user(c, (unsigned long __user *)src, efault);
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
61 if (unlikely(max <= sizeof(unsigned long)))
62 break;
63 max -= sizeof(unsigned long);
64 unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
65 }
66 res -= align;
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72 if (res >= count)
73 return count+1;
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79efault:
80 return 0;
81}
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104long strnlen_user(const char __user *str, long count)
105{
106 unsigned long max_addr, src_addr;
107
108 if (unlikely(count <= 0))
109 return 0;
110
111 max_addr = user_addr_max();
112 src_addr = (unsigned long)str;
113 if (likely(src_addr < max_addr)) {
114 unsigned long max = max_addr - src_addr;
115 long retval;
116
117 user_access_begin();
118 retval = do_strnlen_user(str, count, max);
119 user_access_end();
120 return retval;
121 }
122 return 0;
123}
124EXPORT_SYMBOL(strnlen_user);
125