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0001 #include <linux/kernel.h>
0002 #include <linux/export.h>
0003 #include <linux/uaccess.h>
0004 
0005 #include <asm/word-at-a-time.h>
0006 
0007 /* Set bits in the first 'n' bytes when loaded from memory */
0008 #ifdef __LITTLE_ENDIAN
0009 #  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
0010 #else
0011 #  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
0012 #endif
0013 
0014 /*
0015  * Do a strnlen, return length of string *with* final '\0'.
0016  * 'count' is the user-supplied count, while 'max' is the
0017  * address space maximum.
0018  *
0019  * Return 0 for exceptions (which includes hitting the address
0020  * space maximum), or 'count+1' if hitting the user-supplied
0021  * maximum count.
0022  *
0023  * NOTE! We can sometimes overshoot the user-supplied maximum
0024  * if it fits in a aligned 'long'. The caller needs to check
0025  * the return value against "> max".
0026  */
0027 static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
0028 {
0029     const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
0030     long align, res = 0;
0031     unsigned long c;
0032 
0033     /*
0034      * Truncate 'max' to the user-specified limit, so that
0035      * we only have one limit we need to check in the loop
0036      */
0037     if (max > count)
0038         max = count;
0039 
0040     /*
0041      * Do everything aligned. But that means that we
0042      * need to also expand the maximum..
0043      */
0044     align = (sizeof(long) - 1) & (unsigned long)src;
0045     src -= align;
0046     max += align;
0047 
0048     unsafe_get_user(c, (unsigned long __user *)src, efault);
0049     c |= aligned_byte_mask(align);
0050 
0051     for (;;) {
0052         unsigned long data;
0053         if (has_zero(c, &data, &constants)) {
0054             data = prep_zero_mask(c, data, &constants);
0055             data = create_zero_mask(data);
0056             return res + find_zero(data) + 1 - align;
0057         }
0058         res += sizeof(unsigned long);
0059         /* We already handled 'unsigned long' bytes. Did we do it all ? */
0060         if (unlikely(max <= sizeof(unsigned long)))
0061             break;
0062         max -= sizeof(unsigned long);
0063         unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
0064     }
0065     res -= align;
0066 
0067     /*
0068      * Uhhuh. We hit 'max'. But was that the user-specified maximum
0069      * too? If so, return the marker for "too long".
0070      */
0071     if (res >= count)
0072         return count+1;
0073 
0074     /*
0075      * Nope: we hit the address space limit, and we still had more
0076      * characters the caller would have wanted. That's 0.
0077      */
0078 efault:
0079     return 0;
0080 }
0081 
0082 /**
0083  * strnlen_user: - Get the size of a user string INCLUDING final NUL.
0084  * @str: The string to measure.
0085  * @count: Maximum count (including NUL character)
0086  *
0087  * Context: User context only. This function may sleep if pagefaults are
0088  *          enabled.
0089  *
0090  * Get the size of a NUL-terminated string in user space.
0091  *
0092  * Returns the size of the string INCLUDING the terminating NUL.
0093  * If the string is too long, returns a number larger than @count. User
0094  * has to check the return value against "> count".
0095  * On exception (or invalid count), returns 0.
0096  *
0097  * NOTE! You should basically never use this function. There is
0098  * almost never any valid case for using the length of a user space
0099  * string, since the string can be changed at any time by other
0100  * threads. Use "strncpy_from_user()" instead to get a stable copy
0101  * of the string.
0102  */
0103 long strnlen_user(const char __user *str, long count)
0104 {
0105     unsigned long max_addr, src_addr;
0106 
0107     if (unlikely(count <= 0))
0108         return 0;
0109 
0110     max_addr = user_addr_max();
0111     src_addr = (unsigned long)str;
0112     if (likely(src_addr < max_addr)) {
0113         unsigned long max = max_addr - src_addr;
0114         long retval;
0115 
0116         user_access_begin();
0117         retval = do_strnlen_user(str, count, max);
0118         user_access_end();
0119         return retval;
0120     }
0121     return 0;
0122 }
0123 EXPORT_SYMBOL(strnlen_user);
0124 
0125 /**
0126  * strlen_user: - Get the size of a user string INCLUDING final NUL.
0127  * @str: The string to measure.
0128  *
0129  * Context: User context only. This function may sleep if pagefaults are
0130  *          enabled.
0131  *
0132  * Get the size of a NUL-terminated string in user space.
0133  *
0134  * Returns the size of the string INCLUDING the terminating NUL.
0135  * On exception, returns 0.
0136  *
0137  * If there is a limit on the length of a valid string, you may wish to
0138  * consider using strnlen_user() instead.
0139  */
0140 long strlen_user(const char __user *str)
0141 {
0142     unsigned long max_addr, src_addr;
0143 
0144     max_addr = user_addr_max();
0145     src_addr = (unsigned long)str;
0146     if (likely(src_addr < max_addr)) {
0147         unsigned long max = max_addr - src_addr;
0148         long retval;
0149 
0150         user_access_begin();
0151         retval = do_strnlen_user(str, ~0ul, max);
0152         user_access_end();
0153         return retval;
0154     }
0155     return 0;
0156 }
0157 EXPORT_SYMBOL(strlen_user);