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