C语言 gcc 编译器是否总是将整数放在内存中的字符数组之前?

Question

我正在尝试从HTAOE书中用C语言进行简单的缓冲区溢出。这是代码：

#include<stdio.h>
#include<string.h>
int main(int argc, char *argv[]){
int val0=10;
char buffer_two[8], buffer_one[8];
int val1=5;
strcpy(buffer_one, "one");
strcpy(buffer_two, "two");
printf("[BEFORE] buffer_two is at @%p contains '%s'n", buffer_two, buffer_two);
printf("[BEFORE] buffer_one is at @%p contains '%s'n", buffer_one, buffer_one);
printf("[BEFORE] val1 is @%p and contains '%d' [0x%08x]n", &val1, val1, val1);
printf("[BEFORE] val0 is @%p and contains '%d' [0x%08x]n", &val0, val0, val0);
printf("Copying the argv[1], which is %ld bytes, into buffer_two..n", strlen(argv[1]));
strcpy(buffer_two, argv[1]);
printf("[AFTER] buffer_two is at @%p contains '%s'n", buffer_two, buffer_two);
printf("[AFTER] val1 is @%p and contains '%d' [0x%08x]n", &val1, val1, val1);
printf("[AFTER] val0 is @%p and contains '%d' [0x%08x]n", &val0, val0, val0);
return 0;
}

正常编译后(没有其他标志(，我使用

./overflow_example "啊

其中"AA....."是第一个参数，A 的数量大于 16。正如预期的那样，溢出发生在buffer_one.但我预计溢出也会发生在整数val0或val1中。失败。 我注意到整数放在堆栈中的字符数组之前，例如为什么？所以那里没有发生溢出。输出：

[BEFORE] buffer_two is at @0x7fffa43fa1a8 contains 'two'
[BEFORE] buffer_one is at @0x7fffa43fa1b0 contains 'one'
[BEFORE] val1 is @0x7fffa43fa1a4 and contains '5' [0x00000005]
[BEFORE] val0 is @0x7fffa43fa1a0 and contains '10' [0x0000000a]
Copying the argv[1], which is 45 bytes, into buffer_two..
[AFTER] buffer_two is at @0x7fffa43fa1a8 contains 'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
[AFTER] buffer_one is at @0x7fffa43fa1b0 contains 'AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
[AFTER] val1 is @0x7fffa43fa1a4 and contains '5' [0x00000005]
[AFTER] val0 is @0x7fffa43fa1a0 and contains '10' [0x0000000a]
*** stack smashing detected ***: <unknown> terminated
Aborted (core dumped)

我的问题是我如何指示编译器不将整数放在字符数组之前，而是将它们放在堆栈中的字符数组之后，以便可以溢出。我期待不可能的事情吗？可以这样做吗？还是微不足道的，例如使用 gcc 命令提供标志？

请帮忙。

:)

PS ： 运行 Ubuntu X86-64 机器

Answer 1

你要求帮助你以合理的方式调用未定义的行为，这通常会让你投反对票，因为Stack Overflow是用来编写好的软件，而不是故意利用的软件。

也就是说，您可以尝试将相关变量放在结构中：

int main(int argc, char *argv[]){
struct {
int val0;
char buffer_two[8];
char buffer_one[8];
int val1;
} group = {
.val0 = 10,
.val1 = 5,
};

strcpy(group.buffer_one, "one");
strcpy(group.buffer_two, "two");
// ...
}