blob: 33f655ef48cd1668604a1f60c4a97e4acbf52508 [file] [log] [blame]
Rasmus Villemoesbf3c2d62015-02-12 15:03:16 -08001#include <linux/compiler.h>
2#include <linux/export.h>
Andrey Ryabinin1771c6e2016-05-20 16:59:31 -07003#include <linux/kasan-checks.h>
David S. Miller29225852012-05-24 13:12:28 -07004#include <linux/uaccess.h>
5#include <linux/kernel.h>
6#include <linux/errno.h>
7
8#include <asm/byteorder.h>
Linus Torvalds36126f82012-05-26 10:43:17 -07009#include <asm/word-at-a-time.h>
David S. Miller29225852012-05-24 13:12:28 -070010
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 */
24static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
25{
Linus Torvalds36126f82012-05-26 10:43:17 -070026 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
David S. Miller29225852012-05-24 13:12:28 -070027 long res = 0;
28
29 /*
30 * Truncate 'max' to the user-specified limit, so that
31 * we only have one limit we need to check in the loop
32 */
33 if (max > count)
34 max = count;
35
36 if (IS_UNALIGNED(src, dst))
37 goto byte_at_a_time;
38
39 while (max >= sizeof(unsigned long)) {
Linus Torvalds36126f82012-05-26 10:43:17 -070040 unsigned long c, data;
David S. Miller29225852012-05-24 13:12:28 -070041
42 /* Fall back to byte-at-a-time if we get a page fault */
Linus Torvalds9fd44702015-12-17 10:05:19 -080043 if (unlikely(unsafe_get_user(c,(unsigned long __user *)(src+res))))
David S. Miller29225852012-05-24 13:12:28 -070044 break;
David S. Miller29225852012-05-24 13:12:28 -070045 *(unsigned long *)(dst+res) = c;
Linus Torvalds36126f82012-05-26 10:43:17 -070046 if (has_zero(c, &data, &constants)) {
47 data = prep_zero_mask(c, data, &constants);
48 data = create_zero_mask(data);
49 return res + find_zero(data);
David S. Miller29225852012-05-24 13:12:28 -070050 }
51 res += sizeof(unsigned long);
52 max -= sizeof(unsigned long);
53 }
54
55byte_at_a_time:
56 while (max) {
57 char c;
58
Linus Torvalds9fd44702015-12-17 10:05:19 -080059 if (unlikely(unsafe_get_user(c,src+res)))
David S. Miller29225852012-05-24 13:12:28 -070060 return -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 return -EFAULT;
80}
81
82/**
83 * strncpy_from_user: - Copy a NUL terminated string from userspace.
84 * @dst: Destination address, in kernel space. This buffer must be at
85 * least @count bytes long.
86 * @src: Source address, in user space.
87 * @count: Maximum number of bytes to copy, including the trailing NUL.
88 *
89 * Copies a NUL-terminated string from userspace to kernel space.
90 *
91 * On success, returns the length of the string (not including the trailing
92 * NUL).
93 *
94 * If access to userspace fails, returns -EFAULT (some data may have been
95 * copied).
96 *
97 * If @count is smaller than the length of the string, copies @count bytes
98 * and returns @count.
99 */
100long strncpy_from_user(char *dst, const char __user *src, long count)
101{
102 unsigned long max_addr, src_addr;
103
104 if (unlikely(count <= 0))
105 return 0;
106
107 max_addr = user_addr_max();
108 src_addr = (unsigned long)src;
109 if (likely(src_addr < max_addr)) {
110 unsigned long max = max_addr - src_addr;
Linus Torvalds9fd44702015-12-17 10:05:19 -0800111 long retval;
112
Andrey Ryabinin1771c6e2016-05-20 16:59:31 -0700113 kasan_check_write(dst, count);
Linus Torvalds9fd44702015-12-17 10:05:19 -0800114 user_access_begin();
115 retval = do_strncpy_from_user(dst, src, count, max);
116 user_access_end();
117 return retval;
David S. Miller29225852012-05-24 13:12:28 -0700118 }
119 return -EFAULT;
120}
121EXPORT_SYMBOL(strncpy_from_user);