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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 | */ |
27 | static 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 | if (unlikely(max < sizeof(unsigned long))) |
61 | break; |
62 | max -= sizeof(unsigned long); |
63 | if (unlikely(__get_user(c,(unsigned long __user *)(src+res)))) |
64 | return 0; |
65 | } |
66 | res -= align; |
67 | |
68 | /* |
69 | * Uhhuh. We hit 'max'. But was that the user-specified maximum |
70 | * too? If so, return the marker for "too long". |
71 | */ |
72 | if (res >= count) |
73 | return count+1; |
74 | |
75 | /* |
76 | * Nope: we hit the address space limit, and we still had more |
77 | * characters the caller would have wanted. That's 0. |
78 | */ |
79 | return 0; |
80 | } |
81 | |
82 | /** |
83 | * strnlen_user: - Get the size of a user string INCLUDING final NUL. |
84 | * @str: The string to measure. |
85 | * @count: Maximum count (including NUL character) |
86 | * |
87 | * Context: User context only. This function may sleep. |
88 | * |
89 | * Get the size of a NUL-terminated string in user space. |
90 | * |
91 | * Returns the size of the string INCLUDING the terminating NUL. |
92 | * If the string is too long, returns 'count+1'. |
93 | * On exception (or invalid count), returns 0. |
94 | */ |
95 | long strnlen_user(const char __user *str, long count) |
96 | { |
97 | unsigned long max_addr, src_addr; |
98 | |
99 | if (unlikely(count <= 0)) |
100 | return 0; |
101 | |
102 | max_addr = user_addr_max(); |
103 | src_addr = (unsigned long)str; |
104 | if (likely(src_addr < max_addr)) { |
105 | unsigned long max = max_addr - src_addr; |
106 | return do_strnlen_user(str, count, max); |
107 | } |
108 | return 0; |
109 | } |
110 | EXPORT_SYMBOL(strnlen_user); |
111 | |
112 | /** |
113 | * strlen_user: - Get the size of a user string INCLUDING final NUL. |
114 | * @str: The string to measure. |
115 | * |
116 | * Context: User context only. This function may sleep. |
117 | * |
118 | * Get the size of a NUL-terminated string in user space. |
119 | * |
120 | * Returns the size of the string INCLUDING the terminating NUL. |
121 | * On exception, returns 0. |
122 | * |
123 | * If there is a limit on the length of a valid string, you may wish to |
124 | * consider using strnlen_user() instead. |
125 | */ |
126 | long strlen_user(const char __user *str) |
127 | { |
128 | unsigned long max_addr, src_addr; |
129 | |
130 | max_addr = user_addr_max(); |
131 | src_addr = (unsigned long)str; |
132 | if (likely(src_addr < max_addr)) { |
133 | unsigned long max = max_addr - src_addr; |
134 | return do_strnlen_user(str, ~0ul, max); |
135 | } |
136 | return 0; |
137 | } |
138 | EXPORT_SYMBOL(strlen_user); |
139 |
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