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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 */
23static 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 */
67efault:
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 */
92long 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}
120EXPORT_SYMBOL(strnlen_user);
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 */
27static 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 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 */
78efault:
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 */
103long 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}
123EXPORT_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 */
140long 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}
157EXPORT_SYMBOL(strlen_user);