// SPDX-License-Identifier: GPL-2.0#include <linux/kernel.h>#include <linux/export.h>#include <linux/uaccess.h>#include <linux/mm.h>#include <linux/bitops.h> #include <asm/word-at-a-time.h> /* * 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 __always_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;	unsigned long align, res = 0;	unsigned long c; 	/*	 * Do everything aligned. But that means that we	 * need to also expand the maximum..	 */	align = (sizeof(unsigned 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);		unsafe_get_user(c, (unsigned long __user *)(src+res), efault);	}	res -= align; 	/*	 * Uhhuh. We hit 'max'. But was that the user-specified maximum	 * too? If so, return the marker for "too long".	 */	if (res >= count)		return count+1; 	/*	 * Nope: we hit the address space limit, and we still had more	 * characters the caller would have wanted. That's 0.	 */efault:	return 0;} /** * strnlen_user: - Get the size of a user string INCLUDING final NUL. * @str: The string to measure. * @count: Maximum count (including NUL character) * * Context: User context only. This function may sleep if pagefaults are *          enabled. * * Get the size of a NUL-terminated string in user space. * * Returns the size of the string INCLUDING the terminating NUL. * If the string is too long, returns a number larger than @count. User * has to check the return value against "> count". * On exception (or invalid count), returns 0. * * NOTE! You should basically never use this function. There is * almost never any valid case for using the length of a user space * string, since the string can be changed at any time by other * threads. Use "strncpy_from_user()" instead to get a stable copy * of the string. */long strnlen_user(const char __user *str, long count){	unsigned long max_addr, src_addr; 	if (unlikely(count <= 0))		return 0; 	if (can_do_masked_user_access()) {		long retval; 		str = masked_user_read_access_begin(str);		retval = do_strnlen_user(str, count, count);		user_read_access_end();		return retval;	} 	max_addr = TASK_SIZE_MAX;	src_addr = (unsigned long)untagged_addr(str);	if (likely(src_addr < max_addr)) {		unsigned long max = max_addr - src_addr;		long retval; 		/*		 * 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; 		if (user_read_access_begin(str, max)) {			retval = do_strnlen_user(str, count, max);			user_read_access_end();			return retval;		}	}	return 0;}EXPORT_SYMBOL(strnlen_user);