1 #include <linux/compiler.h>
2 #include <linux/export.h>
3 #include <linux/thread_info.h>
4 #include <linux/uaccess.h>
5 #include <linux/kernel.h>
6 #include <linux/errno.h>
7
8 #include <asm/byteorder.h>
9 #include <asm/word-at-a-time.h>
10
11 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
12 #define IS_UNALIGNED(src, dst) 0
13 #else
14 #define IS_UNALIGNED(src, dst) \
15 (((long) dst | (long) src) & (sizeof(long) - 1))
16 #endif
17
18 /*
19 * Do a strncpy, return length of string without final '\0'.
20 * 'count' is the user-supplied count (return 'count' if we
21 * hit it), 'max' is the address space maximum (and we return
22 * -EFAULT if we hit it).
23 */
do_strncpy_from_user(char * dst,const char __user * src,unsigned long count,unsigned long max)24 static inline long do_strncpy_from_user(char *dst, const char __user *src,
25 unsigned long count, unsigned long max)
26 {
27 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
28 unsigned long res = 0;
29
30 /*
31 * Truncate 'max' to the user-specified limit, so that
32 * we only have one limit we need to check in the loop
33 */
34 if (max > count)
35 max = count;
36
37 if (IS_UNALIGNED(src, dst))
38 goto byte_at_a_time;
39
40 while (max >= sizeof(unsigned long)) {
41 unsigned long c, data;
42
43 /* Fall back to byte-at-a-time if we get a page fault */
44 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
45
46 *(unsigned long *)(dst+res) = c;
47 if (has_zero(c, &data, &constants)) {
48 data = prep_zero_mask(c, data, &constants);
49 data = create_zero_mask(data);
50 return res + find_zero(data);
51 }
52 res += sizeof(unsigned long);
53 max -= sizeof(unsigned long);
54 }
55
56 byte_at_a_time:
57 while (max) {
58 char c;
59
60 unsafe_get_user(c,src+res, efault);
61 dst[res] = c;
62 if (!c)
63 return res;
64 res++;
65 max--;
66 }
67
68 /*
69 * Uhhuh. We hit 'max'. But was that the user-specified maximum
70 * too? If so, that's ok - we got as much as the user asked for.
71 */
72 if (res >= count)
73 return res;
74
75 /*
76 * Nope: we hit the address space limit, and we still had more
77 * characters the caller would have wanted. That's an EFAULT.
78 */
79 efault:
80 return -EFAULT;
81 }
82
83 /**
84 * strncpy_from_user: - Copy a NUL terminated string from userspace.
85 * @dst: Destination address, in kernel space. This buffer must be at
86 * least @count bytes long.
87 * @src: Source address, in user space.
88 * @count: Maximum number of bytes to copy, including the trailing NUL.
89 *
90 * Copies a NUL-terminated string from userspace to kernel space.
91 *
92 * On success, returns the length of the string (not including the trailing
93 * NUL).
94 *
95 * If access to userspace fails, returns -EFAULT (some data may have been
96 * copied).
97 *
98 * If @count is smaller than the length of the string, copies @count bytes
99 * and returns @count.
100 */
strncpy_from_user(char * dst,const char __user * src,long count)101 long strncpy_from_user(char *dst, const char __user *src, long count)
102 {
103 unsigned long max_addr, src_addr;
104
105 if (unlikely(count <= 0))
106 return 0;
107
108 max_addr = user_addr_max();
109 src_addr = (unsigned long)src;
110 if (likely(src_addr < max_addr)) {
111 unsigned long max = max_addr - src_addr;
112 long retval;
113
114 check_object_size(dst, count, false);
115 user_access_begin();
116 retval = do_strncpy_from_user(dst, src, count, max);
117 user_access_end();
118 return retval;
119 }
120 return -EFAULT;
121 }
122 EXPORT_SYMBOL(strncpy_from_user);
123