1
2#include <linux/compiler.h>
3#include <linux/export.h>
4#include <linux/fault-inject-usercopy.h>
5#include <linux/kasan-checks.h>
6#include <linux/thread_info.h>
7#include <linux/uaccess.h>
8#include <linux/kernel.h>
9#include <linux/errno.h>
10#include <linux/mm.h>
11
12#include <asm/byteorder.h>
13#include <asm/word-at-a-time.h>
14
15#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
16#define IS_UNALIGNED(src, dst) 0
17#else
18#define IS_UNALIGNED(src, dst) \
19 (((long) dst | (long) src) & (sizeof(long) - 1))
20#endif
21
22
23
24
25
26
27
28static inline long do_strncpy_from_user(char *dst, const char __user *src,
29 unsigned long count, unsigned long max)
30{
31 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
32 unsigned long res = 0;
33
34 if (IS_UNALIGNED(src, dst))
35 goto byte_at_a_time;
36
37 while (max >= sizeof(unsigned long)) {
38 unsigned long c, data, mask;
39
40
41 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
42
43
44
45
46
47
48
49
50
51
52
53
54 if (has_zero(c, &data, &constants)) {
55 data = prep_zero_mask(c, data, &constants);
56 data = create_zero_mask(data);
57 mask = zero_bytemask(data);
58 *(unsigned long *)(dst+res) = c & mask;
59 return res + find_zero(data);
60 }
61
62 *(unsigned long *)(dst+res) = c;
63
64 res += sizeof(unsigned long);
65 max -= sizeof(unsigned long);
66 }
67
68byte_at_a_time:
69 while (max) {
70 char c;
71
72 unsafe_get_user(c,src+res, efault);
73 dst[res] = c;
74 if (!c)
75 return res;
76 res++;
77 max--;
78 }
79
80
81
82
83
84 if (res >= count)
85 return res;
86
87
88
89
90
91efault:
92 return -EFAULT;
93}
94
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111
112
113long strncpy_from_user(char *dst, const char __user *src, long count)
114{
115 unsigned long max_addr, src_addr;
116
117 might_fault();
118 if (should_fail_usercopy())
119 return -EFAULT;
120 if (unlikely(count <= 0))
121 return 0;
122
123 max_addr = user_addr_max();
124 src_addr = (unsigned long)untagged_addr(src);
125 if (likely(src_addr < max_addr)) {
126 unsigned long max = max_addr - src_addr;
127 long retval;
128
129
130
131
132
133 if (max > count)
134 max = count;
135
136 kasan_check_write(dst, count);
137 check_object_size(dst, count, false);
138 if (user_read_access_begin(src, max)) {
139 retval = do_strncpy_from_user(dst, src, count, max);
140 user_read_access_end();
141 return retval;
142 }
143 }
144 return -EFAULT;
145}
146EXPORT_SYMBOL(strncpy_from_user);
147