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      180527 : static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
      24             : {
      25      180527 :         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
      26      180527 :         unsigned long align, res = 0;
      27      180527 :         unsigned long c;
      28             : 
      29             :         /*
      30             :          * Do everything aligned. But that means that we
      31             :          * need to also expand the maximum..
      32             :          */
      33      180527 :         align = (sizeof(unsigned long) - 1) & (unsigned long)src;
      34      180527 :         src -= align;
      35      180527 :         max += align;
      36             : 
      37      180527 :         unsafe_get_user(c, (unsigned long __user *)src, efault);
      38      180527 :         c |= aligned_byte_mask(align);
      39             : 
      40      659503 :         for (;;) {
      41      659503 :                 unsigned long data;
      42      659503 :                 if (has_zero(c, &data, &constants)) {
      43      180527 :                         data = prep_zero_mask(c, data, &constants);
      44      180527 :                         data = create_zero_mask(data);
      45      180527 :                         return res + find_zero(data) + 1 - align;
      46             :                 }
      47      478976 :                 res += sizeof(unsigned long);
      48             :                 /* We already handled 'unsigned long' bytes. Did we do it all ? */
      49      478976 :                 if (unlikely(max <= sizeof(unsigned long)))
      50             :                         break;
      51      478976 :                 max -= sizeof(unsigned long);
      52      478976 :                 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           0 : 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      180527 : long strnlen_user(const char __user *str, long count)
      93             : {
      94      180527 :         unsigned long max_addr, src_addr;
      95             : 
      96      180527 :         if (unlikely(count <= 0))
      97             :                 return 0;
      98             : 
      99      180527 :         max_addr = user_addr_max();
     100      180527 :         src_addr = (unsigned long)untagged_addr(str);
     101      180527 :         if (likely(src_addr < max_addr)) {
     102      180527 :                 unsigned long max = max_addr - src_addr;
     103      180527 :                 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      180527 :                 if (max > count)
     110             :                         max = count;
     111             : 
     112      180527 :                 if (user_read_access_begin(str, max)) {
     113      180527 :                         retval = do_strnlen_user(str, count, max);
     114      180527 :                         user_read_access_end();
     115      180527 :                         return retval;
     116             :                 }
     117             :         }
     118             :         return 0;
     119             : }
     120             : EXPORT_SYMBOL(strnlen_user);