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 /* We already handled 'unsigned long' bytes. Did we do it all ? */
61 if (unlikely(max <= sizeof(unsigned long)))
63 max -= sizeof(unsigned long);
64 if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
70 * Uhhuh. We hit 'max'. But was that the user-specified maximum
71 * too? If so, return the marker for "too long".
77 * Nope: we hit the address space limit, and we still had more
78 * characters the caller would have wanted. That's 0.
84 * strnlen_user: - Get the size of a user string INCLUDING final NUL.
85 * @str: The string to measure.
86 * @count: Maximum count (including NUL character)
88 * Context: User context only. This function may sleep if pagefaults are
91 * Get the size of a NUL-terminated string in user space.
93 * Returns the size of the string INCLUDING the terminating NUL.
94 * If the string is too long, returns a number larger than @count. User
95 * has to check the return value against "> count".
96 * On exception (or invalid count), returns 0.
98 * NOTE! You should basically never use this function. There is
99 * almost never any valid case for using the length of a user space
100 * string, since the string can be changed at any time by other
101 * threads. Use "strncpy_from_user()" instead to get a stable copy
104 long strnlen_user(const char __user *str, long count)
106 unsigned long max_addr, src_addr;
108 if (unlikely(count <= 0))
111 max_addr = user_addr_max();
112 src_addr = (unsigned long)str;
113 if (likely(src_addr < max_addr)) {
114 unsigned long max = max_addr - src_addr;
115 return do_strnlen_user(str, count, max);
119 EXPORT_SYMBOL(strnlen_user);
122 * strlen_user: - Get the size of a user string INCLUDING final NUL.
123 * @str: The string to measure.
125 * Context: User context only. This function may sleep if pagefaults are
128 * Get the size of a NUL-terminated string in user space.
130 * Returns the size of the string INCLUDING the terminating NUL.
131 * On exception, returns 0.
133 * If there is a limit on the length of a valid string, you may wish to
134 * consider using strnlen_user() instead.
136 long strlen_user(const char __user *str)
138 unsigned long max_addr, src_addr;
140 max_addr = user_addr_max();
141 src_addr = (unsigned long)str;
142 if (likely(src_addr < max_addr)) {
143 unsigned long max = max_addr - src_addr;
144 return do_strnlen_user(str, ~0ul, max);
148 EXPORT_SYMBOL(strlen_user);