int fd = open(“/home/wsxk/test.txt”, O_RDWR)
printf(“%d\n”, fd)

#include <stdio.h>
#include <sys/fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int main(){
    char buf[0x1000];
    int fd = open("/dev/urandom",O_RDONLY);
    for(int i=0;i<50000;i++){
        read(fd,buf,0x20);
    }
    return 0;
}

#include <stdio.h>
#include <sys/fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int main(){
    char buf[0x1000];
    FILE * file = fopen("/dev/urandom","r");
    for(int i=0;i<50000;i++){
        fread(buf,1,0x20,file);
    }
    return 0;
}

/* The tag name of this struct is _IO_FILE to preserve historic
   C++ mangled names for functions taking FILE* arguments.
   That name should not be used in new code.  */
struct _IO_FILE
{
  int _flags;		/* High-order word is _IO_MAGIC; rest is flags. */

  /* The following pointers correspond to the C++ streambuf protocol. */
  char *_IO_read_ptr;	/* Current read pointer */
  char *_IO_read_end;	/* End of get area. */
  char *_IO_read_base;	/* Start of putback+get area. */
  char *_IO_write_base;	/* Start of put area. */
  char *_IO_write_ptr;	/* Current put pointer. */
  char *_IO_write_end;	/* End of put area. */
  char *_IO_buf_base;	/* Start of reserve area. */
  char *_IO_buf_end;	/* End of reserve area. */

  /* The following fields are used to support backing up and undo. */
  char *_IO_save_base; /* Pointer to start of non-current get area. */
  char *_IO_backup_base;  /* Pointer to first valid character of backup area */
  char *_IO_save_end; /* Pointer to end of non-current get area. */

  struct _IO_marker *_markers;

  struct _IO_FILE *_chain;

  int _fileno;
  int _flags2;
  __off_t _old_offset; /* This used to be _offset but it's too small.  */

  /* 1+column number of pbase(); 0 is unknown. */
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];

  _IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};

struct _IO_FILE_complete
{
  struct _IO_FILE _file;
#endif
  __off64_t _offset;
  /* Wide character stream stuff.  */
  struct _IO_codecvt *_codecvt;
  struct _IO_wide_data *_wide_data;
  struct _IO_FILE *_freeres_list;
  void *_freeres_buf;
  size_t __pad5;
  int _mode;
  /* Make sure we don't get into trouble again.  */
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
};

int _flags;		/* High-order word is _IO_MAGIC; rest is flags. */
//字面意思，高2字节代表file struct结构
#define _IO_MAGIC         0xFBAD0000 /* Magic number */ 
//低2字节就表示某些标识
#define _IO_UNBUFFERED        0x0002 //有这个标志就表示关闭buffer功能，本质上和open/read/write一样
#define _IO_NO_READS          0x0004 /* Reading not allowed.  */
#define _IO_NO_WRITES         0x0008 /* Writing not allowed.  */
#define _IO_CURRENTLY_PUTTING 0x0800
#define _IO_IS_APPENDING      0x1000

/* The following pointers correspond to the C++ streambuf protocol. */
char *_IO_read_ptr;	/* Current read pointer */
char *_IO_read_end;	/* End of get area. */
char *_IO_read_base;	/* Start of putback+get area. */
char *_IO_write_base;	/* Start of put area. */
char *_IO_write_ptr;	/* Current put pointer. */
char *_IO_write_end;	/* End of put area. */
char *_IO_buf_base;	/* Start of reserve area. */
char *_IO_buf_end;	/* End of reserve area. */

int _fileno;

#include <stdio.h>
#include <unistd.h>

int win_war = 0;

void win(){
    puts("you win");
}
int main(){
    char buf[256];

    printf("global win_war addr: %p\n",&win_war);
    FILE * file = fopen("./secret","r");
    read(0,file,0x100);
    puts("calling fread!");
    fread(buf,1,10,file);

    if(win_war){
        win();
    }
}

#include <stdio.h>
#include <unistd.h>

char * secret_message = "flag{wsxkwsxk}";

int main(){
    printf("secret_message: %p\n",secret_message);

    FILE * file = fopen("/dev/null","w");
    read(0,file,0x100);

    char buf[256];
    puts("calling fwrite");
    fwrite(buf,1,0x10,file);

    return 0;
}

struct _IO_FILE_plus
{
  FILE file;
  const struct _IO_jump_t *vtable;
};

struct _IO_wide_data
{
  wchar_t *_IO_read_ptr;	/* Current read pointer */
  wchar_t *_IO_read_end;	/* End of get area. */
  wchar_t *_IO_read_base;	/* Start of putback+get area. */
  wchar_t *_IO_write_base;	/* Start of put area. */
  wchar_t *_IO_write_ptr;	/* Current put pointer. */
  wchar_t *_IO_write_end;	/* End of put area. */
  wchar_t *_IO_buf_base;	/* Start of reserve area. */
  wchar_t *_IO_buf_end;		/* End of reserve area. */
  /* The following fields are used to support backing up and undo. */
  wchar_t *_IO_save_base;	/* Pointer to start of non-current get area. */
  wchar_t *_IO_backup_base;	/* Pointer to first valid character of
				   backup area */
  wchar_t *_IO_save_end;	/* Pointer to end of non-current get area. */

  __mbstate_t _IO_state;
  __mbstate_t _IO_last_state;
  struct _IO_codecvt _codecvt;

  wchar_t _shortbuf[1];

  const struct _IO_jump_t *_wide_vtable;
};