LeetCode实现strStr触发heap-buffer-overflow错误原因咨询

该问题对应LeetCode平台的*实现strStr*编程题。本地编译运行自行编写的C语言题解代码可正常执行，但提交到LeetCode平台运行时触发异常报错，无法定位问题根源。

#include <stdio.h>
#include <stdlib.h>

int strStr(char *haystack, char *needle) {
    if (needle[0] == '\0')
        return 0;

    int i = 0;
    int j = 0;

    while (haystack[i] != '\0') {
        while (haystack[i] == needle[j] && haystack[i] != '\0' && needle[j] != '\0') {
            i++;
            j++;
        }

        if (needle[j] == '\0') {
            return i - j;
        } else {
            j = 0;
        }

        i++;
    }
    return -1;
}

int main() {

    printf("%d\n", strStr("aaa", "aaaa"));

    return 0;
}

=================================================================
==32==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000014 at pc 0x5620a8c4472e bp 0x7fff98a004c0 sp 0x7fff98a004b0
READ of size 1 at 0x602000000014 thread T0
    #2 0x7fdce2ee00b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
0x602000000014 is located 0 bytes to the right of 4-byte region [0x602000000010,0x602000000014)
allocated by thread T0 here:
    #0 0x7fdce3b25bc8 in malloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dbc8)
    #3 0x7fdce2ee00b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
Shadow bytes around the buggy address:
  0x0c047fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c047fff8000: fa fa[04]fa fa fa 05 fa fa fa fa fa fa fa fa fa
  0x0c047fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==32==ABORTING

该heap-buffer-overflow（堆缓冲区越界读）由代码下标访问逻辑错误导致，具体触发流程：

• 以测试用例haystack = "aaa"、needle = "aaaa"为例，两个字符串前3个字符完全匹配，内层while循环会连续执行3次i++、j++，执行后i=3（指向haystack的结束符\0，属于合法访问位置），j=3（指向needle的第4个字符'a'）。
• 内层循环判断条件顺序存在缺陷：优先判断haystack[i] == needle[j]，再校验字符串是否到达末尾。此时haystack[3]是结束符，和needle[3]的'a'不相等，内层循环退出。代码重置j=0后，执行外层循环逻辑里的i++，i变为4。
• 下一轮外层while循环启动时，首先访问haystack[4]，而"aaa"包含结束符总共仅占4字节内存，合法索引范围是0-3，访问索引4已经超出堆上分配的内存边界，直接触发地址消毒器的越界报错。
• 本地运行未报错是因为本地编译默认未开启地址消毒检测，越界位置的内存值恰好未触发程序崩溃，属于C语言未定义行为的偶然正常表现，不代表代码逻辑正确。

内容的提问来源于stack exchange，提问作者altair00