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 */
 23static 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	align = (sizeof(unsigned long) - 1) & (unsigned long)src;
 34	src -= align;
 35	max += align;
 36
 37	unsafe_get_user(c, (unsigned long __user *)src, efault);
 38	c |= aligned_byte_mask(align);
 39
 40	for (;;) {
 41		unsigned long data;
 42		if (has_zero(c, &data, &constants)) {
 43			data = prep_zero_mask(c, data, &constants);
 44			data = create_zero_mask(data);
 45			return res + find_zero(data) + 1 - align;
 46		}
 47		res += sizeof(unsigned long);
 48		/* We already handled 'unsigned long' bytes. Did we do it all ? */
 49		if (unlikely(max <= sizeof(unsigned long)))
 50			break;
 51		max -= sizeof(unsigned long);
 52		unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
 53	}
 54	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	if (res >= count)
 61		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	 */
 67efault:
 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 */
 92long strnlen_user(const char __user *str, long count)
 93{
 94	unsigned long max_addr, src_addr;
 95
 96	if (unlikely(count <= 0))
 97		return 0;
 98
 99	max_addr = user_addr_max();
 
 
 
 
 
 
 
 
 
100	src_addr = (unsigned long)untagged_addr(str);
101	if (likely(src_addr < max_addr)) {
102		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		if (max > count)
110			max = count;
111
112		if (user_read_access_begin(str, max)) {
113			retval = do_strnlen_user(str, count, max);
114			user_read_access_end();
115			return retval;
116		}
117	}
118	return 0;
119}
120EXPORT_SYMBOL(strnlen_user);

  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 */
 23static __always_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	align = (sizeof(unsigned long) - 1) & (unsigned long)src;
 34	src -= align;
 35	max += align;
 36
 37	unsafe_get_user(c, (unsigned long __user *)src, efault);
 38	c |= aligned_byte_mask(align);
 39
 40	for (;;) {
 41		unsigned long data;
 42		if (has_zero(c, &data, &constants)) {
 43			data = prep_zero_mask(c, data, &constants);
 44			data = create_zero_mask(data);
 45			return res + find_zero(data) + 1 - align;
 46		}
 47		res += sizeof(unsigned long);
 48		/* We already handled 'unsigned long' bytes. Did we do it all ? */
 49		if (unlikely(max <= sizeof(unsigned long)))
 50			break;
 51		max -= sizeof(unsigned long);
 52		unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
 53	}
 54	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	if (res >= count)
 61		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	 */
 67efault:
 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 */
 92long strnlen_user(const char __user *str, long count)
 93{
 94	unsigned long max_addr, src_addr;
 95
 96	if (unlikely(count <= 0))
 97		return 0;
 98
 99	if (can_do_masked_user_access()) {
100		long retval;
101
102		str = masked_user_access_begin(str);
103		retval = do_strnlen_user(str, count, count);
104		user_read_access_end();
105		return retval;
106	}
107
108	max_addr = TASK_SIZE_MAX;
109	src_addr = (unsigned long)untagged_addr(str);
110	if (likely(src_addr < max_addr)) {
111		unsigned long max = max_addr - src_addr;
112		long retval;
113
114		/*
115		 * Truncate 'max' to the user-specified limit, so that
116		 * we only have one limit we need to check in the loop
117		 */
118		if (max > count)
119			max = count;
120
121		if (user_read_access_begin(str, max)) {
122			retval = do_strnlen_user(str, count, max);
123			user_read_access_end();
124			return retval;
125		}
126	}
127	return 0;
128}
129EXPORT_SYMBOL(strnlen_user);