1 #include <linux/kernel.h>
2 #include <linux/export.h>
3 #include <linux/uaccess.h>
4
5 #include <asm/word-at-a-time.h>
6
7 /* Set bits in the first 'n' bytes when loaded from memory */
8 #ifdef __LITTLE_ENDIAN
9 # define aligned_byte_mask(n) ((1ul << 8*(n))-1)
10 #else
11 # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
12 #endif
13
14 /*
15 * Do a strnlen, return length of string *with* final '\0'.
16 * 'count' is the user-supplied count, while 'max' is the
17 * address space maximum.
18 *
19 * Return 0 for exceptions (which includes hitting the address
20 * space maximum), or 'count+1' if hitting the user-supplied
21 * maximum count.
22 *
23 * NOTE! We can sometimes overshoot the user-supplied maximum
24 * if it fits in a aligned 'long'. The caller needs to check
25 * the return value against "> max".
26 */
do_strnlen_user(const char __user * src,unsigned long count,unsigned long max)27 static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
28 {
29 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
30 long align, res = 0;
31 unsigned long c;
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 /*
41 * Do everything aligned. But that means that we
42 * need to also expand the maximum..
43 */
44 align = (sizeof(long) - 1) & (unsigned long)src;
45 src -= align;
46 max += align;
47
48 unsafe_get_user(c, (unsigned long __user *)src, efault);
49 c |= aligned_byte_mask(align);
50
51 for (;;) {
52 unsigned long data;
53 if (has_zero(c, &data, &constants)) {
54 data = prep_zero_mask(c, data, &constants);
55 data = create_zero_mask(data);
56 return res + find_zero(data) + 1 - align;
57 }
58 res += sizeof(unsigned long);
59 /* We already handled 'unsigned long' bytes. Did we do it all ? */
60 if (unlikely(max <= sizeof(unsigned long)))
61 break;
62 max -= sizeof(unsigned long);
63 unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
64 }
65 res -= align;
66
67 /*
68 * Uhhuh. We hit 'max'. But was that the user-specified maximum
69 * too? If so, return the marker for "too long".
70 */
71 if (res >= count)
72 return count+1;
73
74 /*
75 * Nope: we hit the address space limit, and we still had more
76 * characters the caller would have wanted. That's 0.
77 */
78 efault:
79 return 0;
80 }
81
82 /**
83 * strnlen_user: - Get the size of a user string INCLUDING final NUL.
84 * @str: The string to measure.
85 * @count: Maximum count (including NUL character)
86 *
87 * Context: User context only. This function may sleep.
88 *
89 * Get the size of a NUL-terminated string in user space.
90 *
91 * Returns the size of the string INCLUDING the terminating NUL.
92 * If the string is too long, returns 'count+1'.
93 * On exception (or invalid count), returns 0.
94 */
strnlen_user(const char __user * str,long count)95 long strnlen_user(const char __user *str, long count)
96 {
97 unsigned long max_addr, src_addr;
98
99 if (unlikely(count <= 0))
100 return 0;
101
102 max_addr = user_addr_max();
103 src_addr = (unsigned long)str;
104 if (likely(src_addr < max_addr)) {
105 unsigned long max = max_addr - src_addr;
106 long retval;
107
108 user_access_begin();
109 retval = do_strnlen_user(str, count, max);
110 user_access_end();
111 return retval;
112 }
113 return 0;
114 }
115 EXPORT_SYMBOL(strnlen_user);
116
117 /**
118 * strlen_user: - Get the size of a user string INCLUDING final NUL.
119 * @str: The string to measure.
120 *
121 * Context: User context only. This function may sleep.
122 *
123 * Get the size of a NUL-terminated string in user space.
124 *
125 * Returns the size of the string INCLUDING the terminating NUL.
126 * On exception, returns 0.
127 *
128 * If there is a limit on the length of a valid string, you may wish to
129 * consider using strnlen_user() instead.
130 */
strlen_user(const char __user * str)131 long strlen_user(const char __user *str)
132 {
133 unsigned long max_addr, src_addr;
134
135 max_addr = user_addr_max();
136 src_addr = (unsigned long)str;
137 if (likely(src_addr < max_addr)) {
138 unsigned long max = max_addr - src_addr;
139 long retval;
140
141 user_access_begin();
142 retval = do_strnlen_user(str, ~0ul, max);
143 user_access_end();
144 return retval;
145 }
146 return 0;
147 }
148 EXPORT_SYMBOL(strlen_user);
149