bss中的静态指针溢出

Question

我正在使用 w00w00 练习处理 bss 中的静态指针溢出。我将缓冲区和缓冲区指针放入静态结构中以强制溢出指针。否则，它将指针放在缓冲区之前，并且不会发生溢出。

   #include <stdio.h>
   #include <stdlib.h>
   #include <unistd.h>
   #include <string.h>
   #include <errno.h>

   #define BUFSIZE 16
   #define ADDRLEN 4 /* # of bytes in an address */


int main()
   {
        u_long diff;
    struct buf {
    char buf[BUFSIZE];
    char *bufptr  ;
    } ;

    static struct buf a;

    a.bufptr = a.buf, diff = (u_long)a.buf - (u_long)&a.bufptr;

    printf("bufptr (%p) = %p, buf = %p, diff = 0x%x (%d) bytes\n",
            &a.bufptr,a.bufptr, a.buf, diff, diff);

    memset(a.buf, 'A', (u_int)(diff + ADDRLEN));

    printf("bufptr (%p) = %p, buf = %p, diff = 0x%x (%d) bytes\n",
            &a.bufptr, a.bufptr, a.buf, diff, diff);

      return 0;
   }

我目前在使用 AddressSanitizer 时遇到此错误

==27643==ERROR: AddressSanitizer: negative-size-param: (size=-12)

SUMMARY: AddressSanitizer: negative-size-param ??:0 __asan_memset
==27643==ABORTING

是否有强制溢出的标志或方法？

编辑： 我想通了。差异结果是-16。我很生气它看起来像这样

diff = (u_long)&a.bufptr - (u_long)a.buf

现在它工作正常。

Answer 1

尝试大于结构大小但又不足以被解释为负值的大小：

memset(a.buf, 'A', 1024);

还请确保使用 -fno-common 进行编译，如 Asan FAQ 中所述。

bss中的静态指针溢出

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