blob: b53e1b5d80f429e611cd0be58e9ec1079fb68ead [file] [log] [blame]
Greg Kroah-Hartmanb2441312017-11-01 15:07:57 +01001// SPDX-License-Identifier: GPL-2.0
Rasmus Villemoesbf3c2d62015-02-12 15:03:16 -08002#include <linux/compiler.h>
3#include <linux/export.h>
Andrey Ryabinin1771c6e2016-05-20 16:59:31 -07004#include <linux/kasan-checks.h>
Mark Rutlandbf90e562016-10-11 13:51:27 -07005#include <linux/thread_info.h>
David S. Miller29225852012-05-24 13:12:28 -07006#include <linux/uaccess.h>
7#include <linux/kernel.h>
8#include <linux/errno.h>
9
10#include <asm/byteorder.h>
Linus Torvalds36126f82012-05-26 10:43:17 -070011#include <asm/word-at-a-time.h>
David S. Miller29225852012-05-24 13:12:28 -070012
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 */
26static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
27{
Linus Torvalds36126f82012-05-26 10:43:17 -070028 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
David S. Miller29225852012-05-24 13:12:28 -070029 long res = 0;
30
31 /*
32 * Truncate 'max' to the user-specified limit, so that
33 * we only have one limit we need to check in the loop
34 */
35 if (max > count)
36 max = count;
37
38 if (IS_UNALIGNED(src, dst))
39 goto byte_at_a_time;
40
41 while (max >= sizeof(unsigned long)) {
Linus Torvalds36126f82012-05-26 10:43:17 -070042 unsigned long c, data;
David S. Miller29225852012-05-24 13:12:28 -070043
44 /* Fall back to byte-at-a-time if we get a page fault */
Linus Torvalds1bd44032016-08-08 13:02:01 -070045 unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
46
David S. Miller29225852012-05-24 13:12:28 -070047 *(unsigned long *)(dst+res) = c;
Linus Torvalds36126f82012-05-26 10:43:17 -070048 if (has_zero(c, &data, &constants)) {
49 data = prep_zero_mask(c, data, &constants);
50 data = create_zero_mask(data);
51 return res + find_zero(data);
David S. Miller29225852012-05-24 13:12:28 -070052 }
53 res += sizeof(unsigned long);
54 max -= sizeof(unsigned long);
55 }
56
57byte_at_a_time:
58 while (max) {
59 char c;
60
Linus Torvalds1bd44032016-08-08 13:02:01 -070061 unsafe_get_user(c,src+res, efault);
David S. Miller29225852012-05-24 13:12:28 -070062 dst[res] = c;
63 if (!c)
64 return res;
65 res++;
66 max--;
67 }
68
69 /*
70 * Uhhuh. We hit 'max'. But was that the user-specified maximum
71 * too? If so, that's ok - we got as much as the user asked for.
72 */
73 if (res >= count)
74 return res;
75
76 /*
77 * Nope: we hit the address space limit, and we still had more
78 * characters the caller would have wanted. That's an EFAULT.
79 */
Linus Torvalds1bd44032016-08-08 13:02:01 -070080efault:
David S. Miller29225852012-05-24 13:12:28 -070081 return -EFAULT;
82}
83
84/**
85 * strncpy_from_user: - Copy a NUL terminated string from userspace.
86 * @dst: Destination address, in kernel space. This buffer must be at
87 * least @count bytes long.
88 * @src: Source address, in user space.
89 * @count: Maximum number of bytes to copy, including the trailing NUL.
90 *
91 * Copies a NUL-terminated string from userspace to kernel space.
92 *
93 * On success, returns the length of the string (not including the trailing
94 * NUL).
95 *
96 * If access to userspace fails, returns -EFAULT (some data may have been
97 * copied).
98 *
99 * If @count is smaller than the length of the string, copies @count bytes
100 * and returns @count.
101 */
102long strncpy_from_user(char *dst, const char __user *src, long count)
103{
104 unsigned long max_addr, src_addr;
105
106 if (unlikely(count <= 0))
107 return 0;
108
109 max_addr = user_addr_max();
110 src_addr = (unsigned long)src;
111 if (likely(src_addr < max_addr)) {
112 unsigned long max = max_addr - src_addr;
Linus Torvalds9fd44702015-12-17 10:05:19 -0800113 long retval;
114
Andrey Ryabinin1771c6e2016-05-20 16:59:31 -0700115 kasan_check_write(dst, count);
Mark Rutlandbf90e562016-10-11 13:51:27 -0700116 check_object_size(dst, count, false);
Linus Torvalds9fd44702015-12-17 10:05:19 -0800117 user_access_begin();
118 retval = do_strncpy_from_user(dst, src, count, max);
119 user_access_end();
120 return retval;
David S. Miller29225852012-05-24 13:12:28 -0700121 }
122 return -EFAULT;
123}
124EXPORT_SYMBOL(strncpy_from_user);