pwnable.kr brain fuck write-up

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int __cdecl main(int argc, const char **argv, const char **envp)
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{
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  size_t i; // [esp+28h] [ebp-40Ch]
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  char input[1024]; // [esp+2Ch] [ebp-408h] BYREF
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  unsigned int v6; // [esp+42Ch] [ebp-8h]
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  v6 = __readgsdword(0x14u);
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  setvbuf(stdout, 0, 2, 0);
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  setvbuf(stdin, 0, 1, 0);
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  p = (int)&tape;
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  puts("welcome to brainfuck testing system!!");
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  puts("type some brainfuck instructions except [ ]");
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  memset(input, 0, sizeof(input));
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  fgets(input, 1024, stdin);
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  for ( i = 0; i < strlen(input); ++i )
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    do_brainfuck(input[i]);
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  return 0;
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}

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int __cdecl do_brainfuck(char input)
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{
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  int result; // eax
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  _BYTE *v2; // ebx
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  result = input - 43;
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  switch ( input )
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  {
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    case '+':
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      result = p;
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      ++*(_BYTE *)p;
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      break;
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    case ',':
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      v2 = (_BYTE *)p;
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      result = getchar();
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      *v2 = result;
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      break;
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    case '-':
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      result = p;
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      --*(_BYTE *)p;
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      break;
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    case '.':
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      result = putchar(*(char *)p);
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      break;
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    case '<':
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      result = --p;
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      break;
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    case '>':
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      result = ++p;
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      break;
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    case '[':
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      result = puts("[ and ] not supported.");
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      break;
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    default:
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      return result;
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  }
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  return result;
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}