linux-imx

// SPDX-License-Identifier: GPL-2.0

#include <linux/kernel.h>

#include <linux/export.h>

#include <linux/uaccess.h>

​

#include <asm/word-at-a-time.h>

​

/* Set bits in the first 'n' bytes when loaded from memory */

#ifdef __LITTLE_ENDIAN

#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)

#else

#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))

#endif

​

/*

 * Do a strnlen, return length of string *with* final '\0'.

 * 'count' is the user-supplied count, while 'max' is the

 * address space maximum.

 *

 * Return 0 for exceptions (which includes hitting the address

 * space maximum), or 'count+1' if hitting the user-supplied

 * maximum count.

 *

 * NOTE! We can sometimes overshoot the user-supplied maximum

 * if it fits in a aligned 'long'. The caller needs to check

 * the return value against "> max".

 */

static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)

{

    const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;

    long align, res = 0;

    unsigned long c;

​

    /*

     * Truncate 'max' to the user-specified limit, so that

     * we only have one limit we need to check in the loop

     */

    if (max > count)

        max = count;

​

    /*

     * Do everything aligned. But that means that we

     * need to also expand the maximum..

     */

    align = (sizeof(long) - 1) & (unsigned long)src;

    src -= align;

    max += align;

​

    unsafe_get_user(c, (unsigned long __user *)src, efault);

    c |= aligned_byte_mask(align);

​

    for (;;) {

        unsigned long data;

        if (has_zero(c, &data, &constants)) {

            data = prep_zero_mask(c, data, &constants);

            data = create_zero_mask(data);

            return res + find_zero(data) + 1 - align;

        }

        res += sizeof(unsigned long);

        /* We already handled 'unsigned long' bytes. Did we do it all ? */

        if (unlikely(max <= sizeof(unsigned long)))

            break;

        max -= sizeof(unsigned long);