blob: 9ff4f3bbb1aae8861249dcede7208527710f502e
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 | unsigned 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(unsigned long) - 1) & (unsigned long)src; |
45 | src -= align; |
46 | max += align; |
47 | |
48 | unsafe_get_user(c, (unsigned long __user *)src, efault); |
49 | c |= aligned_byte_mask(align); |
50 | |
51 | for (;;) { |
52 | unsigned long data; |
53 | if (has_zero(c, &data, &constants)) { |
54 | data = prep_zero_mask(c, data, &constants); |
55 | data = create_zero_mask(data); |
56 | return res + find_zero(data) + 1 - align; |
57 | } |
58 | res += sizeof(unsigned long); |
59 | /* We already handled 'unsigned long' bytes. Did we do it all ? */ |
60 | if (unlikely(max <= sizeof(unsigned long))) |
61 | break; |
62 | max -= sizeof(unsigned long); |
63 | unsafe_get_user(c, (unsigned long __user *)(src+res), efault); |
64 | } |
65 | res -= align; |
66 | |
67 | /* |
68 | * Uhhuh. We hit 'max'. But was that the user-specified maximum |
69 | * too? If so, return the marker for "too long". |
70 | */ |
71 | if (res >= count) |
72 | return count+1; |
73 | |
74 | /* |
75 | * Nope: we hit the address space limit, and we still had more |
76 | * characters the caller would have wanted. That's 0. |
77 | */ |
78 | efault: |
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 if pagefaults are |
88 | * enabled. |
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 | */ |
103 | long 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 | long retval; |
115 | |
116 | user_access_begin(); |
117 | retval = do_strnlen_user(str, count, max); |
118 | user_access_end(); |
119 | return retval; |
120 | } |
121 | return 0; |
122 | } |
123 | EXPORT_SYMBOL(strnlen_user); |
124 | |
125 | /** |
126 | * strlen_user: - Get the size of a user string INCLUDING final NUL. |
127 | * @str: The string to measure. |
128 | * |
129 | * Context: User context only. This function may sleep if pagefaults are |
130 | * enabled. |
131 | * |
132 | * Get the size of a NUL-terminated string in user space. |
133 | * |
134 | * Returns the size of the string INCLUDING the terminating NUL. |
135 | * On exception, returns 0. |
136 | * |
137 | * If there is a limit on the length of a valid string, you may wish to |
138 | * consider using strnlen_user() instead. |
139 | */ |
140 | long strlen_user(const char __user *str) |
141 | { |
142 | unsigned long max_addr, src_addr; |
143 | |
144 | max_addr = user_addr_max(); |
145 | src_addr = (unsigned long)str; |
146 | if (likely(src_addr < max_addr)) { |
147 | unsigned long max = max_addr - src_addr; |
148 | long retval; |
149 | |
150 | user_access_begin(); |
151 | retval = do_strnlen_user(str, ~0ul, max); |
152 | user_access_end(); |
153 | return retval; |
154 | } |
155 | return 0; |
156 | } |
157 | EXPORT_SYMBOL(strlen_user); |
158 |