1 #include <linux/kernel.h>
2 #include <linux/export.h>
3 #include <linux/uaccess.h>
5 #include <asm/word-at-a-time.h>
7 /* Set bits in the first 'n' bytes when loaded from memory */
9 # define aligned_byte_mask(n) ((1ul << 8*(n))-1)
11 # define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
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.
19 * Return 0 for exceptions (which includes hitting the address
20 * space maximum), or 'count+1' if hitting the user-supplied
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".
27 static inline long do_strnlen_user(const char __user
*src
, unsigned long count
, unsigned long max
)
29 const struct word_at_a_time constants
= WORD_AT_A_TIME_CONSTANTS
;
34 * Truncate 'max' to the user-specified limit, so that
35 * we only have one limit we need to check in the loop
41 * Do everything aligned. But that means that we
42 * need to also expand the maximum..
44 align
= (sizeof(long) - 1) & (unsigned long)src
;
48 if (unlikely(__get_user(c
,(unsigned long __user
*)src
)))
50 c
|= aligned_byte_mask(align
);
54 if (has_zero(c
, &data
, &constants
)) {
55 data
= prep_zero_mask(c
, data
, &constants
);
56 data
= create_zero_mask(data
);
57 return res
+ find_zero(data
) + 1 - align
;
59 res
+= sizeof(unsigned long);
60 if (unlikely(max
< sizeof(unsigned long)))
62 max
-= sizeof(unsigned long);
63 if (unlikely(__get_user(c
,(unsigned long __user
*)(src
+res
))))
69 * Uhhuh. We hit 'max'. But was that the user-specified maximum
70 * too? If so, return the marker for "too long".
76 * Nope: we hit the address space limit, and we still had more
77 * characters the caller would have wanted. That's 0.
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)
87 * Context: User context only. This function may sleep.
89 * Get the size of a NUL-terminated string in user space.
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.
95 long strnlen_user(const char __user
*str
, long count
)
97 unsigned long max_addr
, src_addr
;
99 if (unlikely(count
<= 0))
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 return do_strnlen_user(str
, count
, max
);
110 EXPORT_SYMBOL(strnlen_user
);
113 * strlen_user: - Get the size of a user string INCLUDING final NUL.
114 * @str: The string to measure.
116 * Context: User context only. This function may sleep.
118 * Get the size of a NUL-terminated string in user space.
120 * Returns the size of the string INCLUDING the terminating NUL.
121 * On exception, returns 0.
123 * If there is a limit on the length of a valid string, you may wish to
124 * consider using strnlen_user() instead.
126 long strlen_user(const char __user
*str
)
128 unsigned long max_addr
, src_addr
;
130 max_addr
= user_addr_max();
131 src_addr
= (unsigned long)str
;
132 if (likely(src_addr
< max_addr
)) {
133 unsigned long max
= max_addr
- src_addr
;
134 return do_strnlen_user(str
, ~0ul, max
);
138 EXPORT_SYMBOL(strlen_user
);
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