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1// SPDX-License-Identifier: GPL-2.02#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 the13 * address space maximum.14 *15 * Return 0 for exceptions (which includes hitting the address16 * space maximum), or 'count+1' if hitting the user-supplied17 * maximum count.18 *19 * NOTE! We can sometimes overshoot the user-supplied maximum20 * if it fits in a aligned 'long'. The caller needs to check21 * 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 we31 * 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 maximum58 * 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 more65 * 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 are77 * 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. User83 * 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 is87 * almost never any valid case for using the length of a user space88 * string, since the string can be changed at any time by other89 * threads. Use "strncpy_from_user()" instead to get a stable copy90 * 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 that116 * we only have one limit we need to check in the loop117 */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);130