1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/compiler.h>
3 #include <linux/export.h>
4 #include <linux/kasan-checks.h>
5 #include <linux/thread_info.h>
6 #include <linux/uaccess.h>
7 #include <linux/kernel.h>
8 #include <linux/errno.h>
9
10 #include <asm/byteorder.h>
11 #include <asm/word-at-a-time.h>
12
13 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
14 #define IS_UNALIGNED(src, dst) 0
15 #else
16 #define IS_UNALIGNED(src, dst) \
17 (((long) dst | (long) src) & (sizeof(long) - 1))
18 #endif
19
20 /*
21 * Do a strncpy, return length of string without final '\0'.
22 * 'count' is the user-supplied count (return 'count' if we
23 * hit it), 'max' is the address space maximum (and we return
24 * -EFAULT if we hit it).
25 */
do_strncpy_from_user(char * dst,const char __user * src,unsigned long count,unsigned long max)26 static inline long do_strncpy_from_user(char *dst, const char __user *src,
27 unsigned long count, unsigned long max)
28 {
29 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
30 unsigned long res = 0;
31
32 if (IS_UNALIGNED(src, dst))
33 goto byte_at_a_time;
34
35 while (max >= sizeof(unsigned long)) {
36 unsigned long c, data;
37
38 /* Fall back to byte-at-a-time if we get a page fault */
39 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
40
41 *(unsigned long *)(dst+res) = c;
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);
46 }
47 res += sizeof(unsigned long);
48 max -= sizeof(unsigned long);
49 }
50
51 byte_at_a_time:
52 while (max) {
53 char c;
54
55 unsafe_get_user(c,src+res, efault);
56 dst[res] = c;
57 if (!c)
58 return res;
59 res++;
60 max--;
61 }
62
63 /*
64 * Uhhuh. We hit 'max'. But was that the user-specified maximum
65 * too? If so, that's ok - we got as much as the user asked for.
66 */
67 if (res >= count)
68 return res;
69
70 /*
71 * Nope: we hit the address space limit, and we still had more
72 * characters the caller would have wanted. That's an EFAULT.
73 */
74 efault:
75 return -EFAULT;
76 }
77
78 /**
79 * strncpy_from_user: - Copy a NUL terminated string from userspace.
80 * @dst: Destination address, in kernel space. This buffer must be at
81 * least @count bytes long.
82 * @src: Source address, in user space.
83 * @count: Maximum number of bytes to copy, including the trailing NUL.
84 *
85 * Copies a NUL-terminated string from userspace to kernel space.
86 *
87 * On success, returns the length of the string (not including the trailing
88 * NUL).
89 *
90 * If access to userspace fails, returns -EFAULT (some data may have been
91 * copied).
92 *
93 * If @count is smaller than the length of the string, copies @count bytes
94 * and returns @count.
95 */
strncpy_from_user(char * dst,const char __user * src,long count)96 long strncpy_from_user(char *dst, const char __user *src, long count)
97 {
98 unsigned long max_addr, src_addr;
99
100 if (unlikely(count <= 0))
101 return 0;
102
103 max_addr = user_addr_max();
104 src_addr = (unsigned long)src;
105 if (likely(src_addr < max_addr)) {
106 unsigned long max = max_addr - src_addr;
107 long retval;
108
109 /*
110 * Truncate 'max' to the user-specified limit, so that
111 * we only have one limit we need to check in the loop
112 */
113 if (max > count)
114 max = count;
115
116 kasan_check_write(dst, count);
117 check_object_size(dst, count, false);
118 if (user_access_begin(VERIFY_READ, src, max)) {
119 retval = do_strncpy_from_user(dst, src, count, max);
120 user_access_end();
121 return retval;
122 }
123 }
124 return -EFAULT;
125 }
126 EXPORT_SYMBOL(strncpy_from_user);
127