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 #include <linux/mm.h>
10
11 #include <asm/byteorder.h>
12 #include <asm/word-at-a-time.h>
13
14 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
15 #define IS_UNALIGNED(src, dst) 0
16 #else
17 #define IS_UNALIGNED(src, dst) \
18 (((long) dst | (long) src) & (sizeof(long) - 1))
19 #endif
20
21 /*
22 * Do a strncpy, return length of string without final '\0'.
23 * 'count' is the user-supplied count (return 'count' if we
24 * hit it), 'max' is the address space maximum (and we return
25 * -EFAULT if we hit it).
26 */
do_strncpy_from_user(char * dst,const char __user * src,unsigned long count,unsigned long max)27 static inline long do_strncpy_from_user(char *dst, const char __user *src,
28 unsigned long count, unsigned long max)
29 {
30 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
31 unsigned long res = 0;
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 if (IS_UNALIGNED(src, dst))
41 goto byte_at_a_time;
42
43 while (max >= sizeof(unsigned long)) {
44 unsigned long c, data;
45
46 /* Fall back to byte-at-a-time if we get a page fault */
47 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
48
49 *(unsigned long *)(dst+res) = c;
50 if (has_zero(c, &data, &constants)) {
51 data = prep_zero_mask(c, data, &constants);
52 data = create_zero_mask(data);
53 return res + find_zero(data);
54 }
55 res += sizeof(unsigned long);
56 max -= sizeof(unsigned long);
57 }
58
59 byte_at_a_time:
60 while (max) {
61 char c;
62
63 unsafe_get_user(c,src+res, efault);
64 dst[res] = c;
65 if (!c)
66 return res;
67 res++;
68 max--;
69 }
70
71 /*
72 * Uhhuh. We hit 'max'. But was that the user-specified maximum
73 * too? If so, that's ok - we got as much as the user asked for.
74 */
75 if (res >= count)
76 return res;
77
78 /*
79 * Nope: we hit the address space limit, and we still had more
80 * characters the caller would have wanted. That's an EFAULT.
81 */
82 efault:
83 return -EFAULT;
84 }
85
86 /**
87 * strncpy_from_user: - Copy a NUL terminated string from userspace.
88 * @dst: Destination address, in kernel space. This buffer must be at
89 * least @count bytes long.
90 * @src: Source address, in user space.
91 * @count: Maximum number of bytes to copy, including the trailing NUL.
92 *
93 * Copies a NUL-terminated string from userspace to kernel space.
94 *
95 * On success, returns the length of the string (not including the trailing
96 * NUL).
97 *
98 * If access to userspace fails, returns -EFAULT (some data may have been
99 * copied).
100 *
101 * If @count is smaller than the length of the string, copies @count bytes
102 * and returns @count.
103 */
strncpy_from_user(char * dst,const char __user * src,long count)104 long strncpy_from_user(char *dst, const char __user *src, long count)
105 {
106 unsigned long max_addr, src_addr;
107
108 if (unlikely(count <= 0))
109 return 0;
110
111 max_addr = user_addr_max();
112 src_addr = (unsigned long)untagged_addr(src);
113 if (likely(src_addr < max_addr)) {
114 unsigned long max = max_addr - src_addr;
115 long retval;
116
117 kasan_check_write(dst, count);
118 check_object_size(dst, count, false);
119 if (user_access_begin(src, max)) {
120 retval = do_strncpy_from_user(dst, src, count, max);
121 user_access_end();
122 return retval;
123 }
124 }
125 return -EFAULT;
126 }
127 EXPORT_SYMBOL(strncpy_from_user);
128
