Branch data     Line data    Source code

       1                 :            : // SPDX-License-Identifier: GPL-2.0
       2                 :            : #include <linux/kernel.h>
       3                 :            : #include <linux/export.h>
       4                 :            : #include <linux/uaccess.h>
       5                 :            : #include <linux/mm.h>
       6                 :            : #include <linux/bitops.h>
       7                 :            : 
       8                 :            : #include <asm/word-at-a-time.h>
       9                 :            : 
      10                 :            : /*
      11                 :            :  * Do a strnlen, return length of string *with* final '\0'.
      12                 :            :  * 'count' is the user-supplied count, while 'max' is the
      13                 :            :  * address space maximum.
      14                 :            :  *
      15                 :            :  * Return 0 for exceptions (which includes hitting the address
      16                 :            :  * space maximum), or 'count+1' if hitting the user-supplied
      17                 :            :  * maximum count.
      18                 :            :  *
      19                 :            :  * NOTE! We can sometimes overshoot the user-supplied maximum
      20                 :            :  * if it fits in a aligned 'long'. The caller needs to check
      21                 :            :  * the return value against "> max".
      22                 :            :  */
      23                 :          3 : static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
      24                 :            : {
      25                 :            :         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
      26                 :            :         unsigned long align, res = 0;
      27                 :            :         unsigned long c;
      28                 :            : 
      29                 :            :         /*
      30                 :            :          * Do everything aligned. But that means that we
      31                 :            :          * need to also expand the maximum..
      32                 :            :          */
      33                 :          3 :         align = (sizeof(unsigned long) - 1) & (unsigned long)src;
      34                 :          3 :         src -= align;
      35                 :          3 :         max += align;
      36                 :            : 
      37                 :          3 :         unsafe_get_user(c, (unsigned long __user *)src, efault);
      38                 :          3 :         c |= aligned_byte_mask(align);
      39                 :            : 
      40                 :            :         for (;;) {
      41                 :            :                 unsigned long data;
      42                 :          3 :                 if (has_zero(c, &data, &constants)) {
      43                 :          3 :                         data = prep_zero_mask(c, data, &constants);
      44                 :            :                         data = create_zero_mask(data);
      45                 :          3 :                         return res + find_zero(data) + 1 - align;
      46                 :            :                 }
      47                 :          3 :                 res += sizeof(unsigned long);
      48                 :            :                 /* We already handled 'unsigned long' bytes. Did we do it all ? */
      49                 :          3 :                 if (unlikely(max <= sizeof(unsigned long)))
      50                 :            :                         break;
      51                 :          3 :                 max -= sizeof(unsigned long);
      52                 :          3 :                 unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
      53                 :            :         }
      54                 :          0 :         res -= align;
      55                 :            : 
      56                 :            :         /*
      57                 :            :          * Uhhuh. We hit 'max'. But was that the user-specified maximum
      58                 :            :          * too? If so, return the marker for "too long".
      59                 :            :          */
      60                 :          0 :         if (res >= count)
      61                 :          0 :                 return count+1;
      62                 :            : 
      63                 :            :         /*
      64                 :            :          * Nope: we hit the address space limit, and we still had more
      65                 :            :          * characters the caller would have wanted. That's 0.
      66                 :            :          */
      67                 :            : efault:
      68                 :            :         return 0;
      69                 :            : }
      70                 :            : 
      71                 :            : /**
      72                 :            :  * strnlen_user: - Get the size of a user string INCLUDING final NUL.
      73                 :            :  * @str: The string to measure.
      74                 :            :  * @count: Maximum count (including NUL character)
      75                 :            :  *
      76                 :            :  * Context: User context only. This function may sleep if pagefaults are
      77                 :            :  *          enabled.
      78                 :            :  *
      79                 :            :  * Get the size of a NUL-terminated string in user space.
      80                 :            :  *
      81                 :            :  * Returns the size of the string INCLUDING the terminating NUL.
      82                 :            :  * If the string is too long, returns a number larger than @count. User
      83                 :            :  * has to check the return value against "> count".
      84                 :            :  * On exception (or invalid count), returns 0.
      85                 :            :  *
      86                 :            :  * NOTE! You should basically never use this function. There is
      87                 :            :  * almost never any valid case for using the length of a user space
      88                 :            :  * string, since the string can be changed at any time by other
      89                 :            :  * threads. Use "strncpy_from_user()" instead to get a stable copy
      90                 :            :  * of the string.
      91                 :            :  */
      92                 :          3 : long strnlen_user(const char __user *str, long count)
      93                 :            : {
      94                 :            :         unsigned long max_addr, src_addr;
      95                 :            : 
      96                 :          3 :         if (unlikely(count <= 0))
      97                 :            :                 return 0;
      98                 :            : 
      99                 :          3 :         max_addr = user_addr_max();
     100                 :          3 :         src_addr = (unsigned long)untagged_addr(str);
     101                 :          3 :         if (likely(src_addr < max_addr)) {
     102                 :          3 :                 unsigned long max = max_addr - src_addr;
     103                 :            :                 long retval;
     104                 :            : 
     105                 :            :                 /*
     106                 :            :                  * Truncate 'max' to the user-specified limit, so that
     107                 :            :                  * we only have one limit we need to check in the loop
     108                 :            :                  */
     109                 :          3 :                 if (max > count)
     110                 :            :                         max = count;
     111                 :            : 
     112                 :          3 :                 if (user_access_begin(str, max)) {
     113                 :          3 :                         retval = do_strnlen_user(str, count, max);
     114                 :            :                         user_access_end();
     115                 :          3 :                         return retval;
     116                 :            :                 }
     117                 :            :         }
     118                 :            :         return 0;
     119                 :            : }
     120                 :            : EXPORT_SYMBOL(strnlen_user);