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1 | // SPDX-License-Identifier: GPL-2.0 | |
2 | #include <linux/kernel.h> | |
3 | #include <linux/export.h> | |
4 | #include <linux/uaccess.h> | |
5 | #include <linux/mm.h> | |
6 | #include <linux/bitops.h> | |
7 | ||
8 | #include <asm/word-at-a-time.h> | |
9 | ||
10 | /* | |
11 | * Do a strnlen, return length of string *with* final '\0'. | |
12 | * 'count' is the user-supplied count, while 'max' is the | |
13 | * address space maximum. | |
14 | * | |
15 | * Return 0 for exceptions (which includes hitting the address | |
16 | * space maximum), or 'count+1' if hitting the user-supplied | |
17 | * maximum count. | |
18 | * | |
19 | * NOTE! We can sometimes overshoot the user-supplied maximum | |
20 | * if it fits in a aligned 'long'. The caller needs to check | |
21 | * the return value against "> max". | |
22 | */ | |
23 | static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) | |
24 | { | |
25 | const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; | |
26 | unsigned long align, res = 0; | |
27 | unsigned long c; | |
28 | ||
29 | /* | |
30 | * Do everything aligned. But that means that we | |
31 | * need to also expand the maximum.. | |
32 | */ | |
33 | align = (sizeof(unsigned long) - 1) & (unsigned long)src; | |
34 | src -= align; | |
35 | max += align; | |
36 | ||
37 | unsafe_get_user(c, (unsigned long __user *)src, efault); | |
38 | c |= aligned_byte_mask(align); | |
39 | ||
40 | for (;;) { | |
41 | unsigned long data; | |
42 | if (has_zero(c, &data, &constants)) { | |
43 | data = prep_zero_mask(c, data, &constants); | |
44 | data = create_zero_mask(data); | |
45 | return res + find_zero(data) + 1 - align; | |
46 | } | |
47 | res += sizeof(unsigned long); | |
48 | /* We already handled 'unsigned long' bytes. Did we do it all ? */ | |
49 | if (unlikely(max <= sizeof(unsigned long))) | |
50 | break; | |
51 | max -= sizeof(unsigned long); | |
52 | unsafe_get_user(c, (unsigned long __user *)(src+res), efault); | |
53 | } | |
54 | res -= align; | |
55 | ||
56 | /* | |
57 | * Uhhuh. We hit 'max'. But was that the user-specified maximum | |
58 | * too? If so, return the marker for "too long". | |
59 | */ | |
60 | if (res >= count) | |
61 | return count+1; | |
62 | ||
63 | /* | |
64 | * Nope: we hit the address space limit, and we still had more | |
65 | * characters the caller would have wanted. That's 0. | |
66 | */ | |
67 | efault: | |
68 | return 0; | |
69 | } | |
70 | ||
71 | /** | |
72 | * strnlen_user: - Get the size of a user string INCLUDING final NUL. | |
73 | * @str: The string to measure. | |
74 | * @count: Maximum count (including NUL character) | |
75 | * | |
76 | * Context: User context only. This function may sleep if pagefaults are | |
77 | * enabled. | |
78 | * | |
79 | * Get the size of a NUL-terminated string in user space. | |
80 | * | |
81 | * Returns the size of the string INCLUDING the terminating NUL. | |
82 | * If the string is too long, returns a number larger than @count. User | |
83 | * has to check the return value against "> count". | |
84 | * On exception (or invalid count), returns 0. | |
85 | * | |
86 | * NOTE! You should basically never use this function. There is | |
87 | * almost never any valid case for using the length of a user space | |
88 | * string, since the string can be changed at any time by other | |
89 | * threads. Use "strncpy_from_user()" instead to get a stable copy | |
90 | * of the string. | |
91 | */ | |
92 | long strnlen_user(const char __user *str, long count) | |
93 | { | |
94 | unsigned long max_addr, src_addr; | |
95 | ||
96 | if (unlikely(count <= 0)) | |
97 | return 0; | |
98 | ||
99 | max_addr = user_addr_max(); | |
100 | src_addr = (unsigned long)untagged_addr(str); | |
101 | if (likely(src_addr < max_addr)) { | |
102 | unsigned long max = max_addr - src_addr; | |
103 | long retval; | |
104 | ||
105 | /* | |
106 | * Truncate 'max' to the user-specified limit, so that | |
107 | * we only have one limit we need to check in the loop | |
108 | */ | |
109 | if (max > count) | |
110 | max = count; | |
111 | ||
112 | if (user_read_access_begin(str, max)) { | |
113 | retval = do_strnlen_user(str, count, max); | |
114 | user_read_access_end(); | |
115 | return retval; | |
116 | } | |
117 | } | |
118 | return 0; | |
119 | } | |
120 | EXPORT_SYMBOL(strnlen_user); |