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 */
 27static 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	if (unlikely(__get_user(c,(unsigned long __user *)src)))
 49		return 0;
 50	c |= aligned_byte_mask(align);
 51
 52	for (;;) {
 53		unsigned long data;
 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;
 58		}
 59		res += sizeof(unsigned long);
 60		if (unlikely(max < sizeof(unsigned long)))
 61			break;
 62		max -= sizeof(unsigned long);
 63		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
 64			return 0;
 65	}
 66	res -= align;
 67
 68	/*
 69	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
 70	 * too? If so, return the marker for "too long".
 71	 */
 72	if (res >= count)
 73		return count+1;
 74
 75	/*
 76	 * Nope: we hit the address space limit, and we still had more
 77	 * characters the caller would have wanted. That's 0.
 78	 */
 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 */
 95long 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		return do_strnlen_user(str, count, max);
107	}
108	return 0;
109}
110EXPORT_SYMBOL(strnlen_user);
111
112/**
113 * strlen_user: - Get the size of a user string INCLUDING final NUL.
114 * @str: The string to measure.
115 *
116 * Context: User context only.  This function may sleep.
117 *
118 * Get the size of a NUL-terminated string in user space.
119 *
120 * Returns the size of the string INCLUDING the terminating NUL.
121 * On exception, returns 0.
122 *
123 * If there is a limit on the length of a valid string, you may wish to
124 * consider using strnlen_user() instead.
125 */
126long strlen_user(const char __user *str)
127{
128	unsigned long max_addr, src_addr;
129
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);
135	}
136	return 0;
137}
138EXPORT_SYMBOL(strlen_user);