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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
a08c5356 LT |
2 | #include <linux/kernel.h> |
3 | #include <linux/export.h> | |
4 | #include <linux/uaccess.h> | |
903f433f | 5 | #include <linux/mm.h> |
a08c5356 LT |
6 | |
7 | #include <asm/word-at-a-time.h> | |
8 | ||
9 | /* Set bits in the first 'n' bytes when loaded from memory */ | |
10 | #ifdef __LITTLE_ENDIAN | |
11 | # define aligned_byte_mask(n) ((1ul << 8*(n))-1) | |
12 | #else | |
69ea6405 | 13 | # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n))) |
a08c5356 LT |
14 | #endif |
15 | ||
16 | /* | |
17 | * Do a strnlen, return length of string *with* final '\0'. | |
18 | * 'count' is the user-supplied count, while 'max' is the | |
19 | * address space maximum. | |
20 | * | |
21 | * Return 0 for exceptions (which includes hitting the address | |
22 | * space maximum), or 'count+1' if hitting the user-supplied | |
23 | * maximum count. | |
24 | * | |
25 | * NOTE! We can sometimes overshoot the user-supplied maximum | |
26 | * if it fits in a aligned 'long'. The caller needs to check | |
27 | * the return value against "> max". | |
28 | */ | |
29 | static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) | |
30 | { | |
31 | const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; | |
29da93fe | 32 | unsigned long align, res = 0; |
a08c5356 LT |
33 | unsigned long c; |
34 | ||
35 | /* | |
36 | * Truncate 'max' to the user-specified limit, so that | |
37 | * we only have one limit we need to check in the loop | |
38 | */ | |
39 | if (max > count) | |
40 | max = count; | |
41 | ||
42 | /* | |
43 | * Do everything aligned. But that means that we | |
44 | * need to also expand the maximum.. | |
45 | */ | |
29da93fe | 46 | align = (sizeof(unsigned long) - 1) & (unsigned long)src; |
a08c5356 LT |
47 | src -= align; |
48 | max += align; | |
49 | ||
1bd4403d | 50 | unsafe_get_user(c, (unsigned long __user *)src, efault); |
a08c5356 LT |
51 | c |= aligned_byte_mask(align); |
52 | ||
53 | for (;;) { | |
54 | unsigned long data; | |
55 | if (has_zero(c, &data, &constants)) { | |
56 | data = prep_zero_mask(c, data, &constants); | |
57 | data = create_zero_mask(data); | |
58 | return res + find_zero(data) + 1 - align; | |
59 | } | |
60 | res += sizeof(unsigned long); | |
f18c34e4 JK |
61 | /* We already handled 'unsigned long' bytes. Did we do it all ? */ |
62 | if (unlikely(max <= sizeof(unsigned long))) | |
a08c5356 LT |
63 | break; |
64 | max -= sizeof(unsigned long); | |
1bd4403d | 65 | unsafe_get_user(c, (unsigned long __user *)(src+res), efault); |
a08c5356 LT |
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 | */ | |
1bd4403d | 80 | efault: |
a08c5356 LT |
81 | return 0; |
82 | } | |
83 | ||
84 | /** | |
85 | * strnlen_user: - Get the size of a user string INCLUDING final NUL. | |
86 | * @str: The string to measure. | |
87 | * @count: Maximum count (including NUL character) | |
88 | * | |
b3c395ef DH |
89 | * Context: User context only. This function may sleep if pagefaults are |
90 | * enabled. | |
a08c5356 LT |
91 | * |
92 | * Get the size of a NUL-terminated string in user space. | |
93 | * | |
94 | * Returns the size of the string INCLUDING the terminating NUL. | |
226a07ef JK |
95 | * If the string is too long, returns a number larger than @count. User |
96 | * has to check the return value against "> count". | |
a08c5356 | 97 | * On exception (or invalid count), returns 0. |
226a07ef JK |
98 | * |
99 | * NOTE! You should basically never use this function. There is | |
100 | * almost never any valid case for using the length of a user space | |
101 | * string, since the string can be changed at any time by other | |
102 | * threads. Use "strncpy_from_user()" instead to get a stable copy | |
103 | * of the string. | |
a08c5356 LT |
104 | */ |
105 | long strnlen_user(const char __user *str, long count) | |
106 | { | |
107 | unsigned long max_addr, src_addr; | |
108 | ||
109 | if (unlikely(count <= 0)) | |
110 | return 0; | |
111 | ||
112 | max_addr = user_addr_max(); | |
903f433f | 113 | src_addr = (unsigned long)untagged_addr(str); |
a08c5356 LT |
114 | if (likely(src_addr < max_addr)) { |
115 | unsigned long max = max_addr - src_addr; | |
9fd4470f LT |
116 | long retval; |
117 | ||
594cc251 LT |
118 | if (user_access_begin(str, max)) { |
119 | retval = do_strnlen_user(str, count, max); | |
120 | user_access_end(); | |
121 | return retval; | |
122 | } | |
a08c5356 LT |
123 | } |
124 | return 0; | |
125 | } | |
126 | EXPORT_SYMBOL(strnlen_user); |