WinPcap权威指南(一)
WinPcap是一个开源的网络抓包模块,顾名思义,它只能工作在Windows下,但本文介绍的知识并不局限于任何操作系统和开发语言,因为网络协议本身是没有这些区别的。阅读本指南之前,请先下载WinPcap安装到自己的电脑上,目前WinPcap的最新版本是4.1.3,支持基于NT核心的所有操作系统(从NT4一直到Win8),读者可以从官方网站http://www.winpcap.org/install/default.htm下载。
网络其实是分层设计的,一个应用层的网络程序对外通信的时候,大概的流程如下:应用程序(调用WinSock)<--->SPI层<--->TDI层<--->NDIS层<--->MiniPort层<-->物理网卡,实际上,应用程序可以直接调用上面的某一层,例如:直接调用TDI驱动收发网络包;又例如,一般软件防火墙工作于NDIS层,如果你直接使用MiniPort HOOK进行收发数据,那么防火墙是完全不知情的,也不会有任何提示。应用层抓包的话,方法有很多:例如本机的可以使用API HOOK,截取WinSock的调用;或者直接安装一个SPI的HOOK;又或者直接使用RawSocket接口。WinPcap的驱动实际上位于NDIS层,属于NDIS过滤驱动,也就是说,它只是抓包,但不像软件防火墙的passthru模型还可以拦截。另外,它还可以发送数据包。注意:笔者曾经将它翻译为Delphi,发现在以太网环境下(例如局域网)它是通过自己的驱动发布,而对于拨号上网的PPPOE连接,它调用的是微软的NetMon接口,也就是说,如果你的电脑没有安装NetMon,那么在拨号上网的环境下WinpCap可能是无法预期工作的。
调用WinPcap有两种方式,一种是通过packet.dll调用它的驱动npf.sys,另外一种是通过wpcap.dll再间接调用packet.dll来调用它的驱动npf.sys,可能会有人问,既然可以直接调用packet.dll,为什么还要有调用wpcap.dll这种方式?原因很简单:在Unix下(或者Linux)下有一个抓包接口叫Pcap—这也是WinPcap的名称来由,wpcap.dll对外提供了相同的接口函数,便于程序员在不同的平台下移植。本文介绍的是packet.dll调用方式,对wpcap.dll接口感兴趣的朋友可以参考韩国程序员写的一个控件包Snoop2,我将它的下载放在本文的末尾(说句题外话,WinPcap的安装程序,实际上是释放sys和dll到系统,然后安装sys为服务,具体可以参考这个Snoop2(Jingtao修改版),里面直接集成了sys和dll,所以无需先安装WinPcap了,但是由于当时这个版本时间很早,所以还支持Win98系统,读者可以将里面的sys和dll文件替换成现在的最新版本再编译)。
要调用WinPcap,第一步当然是打开需要操作的网卡,因为有可能一台电脑上有好几张网卡。WinPcap提供了一个函数叫PacketGetAdapterNames,用于获取系统已经安装的所有网卡,函数声明如下:
TPacketGetAdapterNames = function(pStr: PAnsiChar; BufferSize: PULONG): Byte; cdecl;
其中pStr是一个用于接收网卡名称的缓冲区,BufferSize是该缓冲区的大小,如果函数成功,则返回非0值。需要注意的是,网络的名称有多种形式,一种是设备名称,一种是友好名称,这个函数返回的格式是:设备名称+两个0+网卡名称,在WinPcap里面打开某块网卡,需要提供的是设备名称,packet.dll的源代码里面大概的实现如下:
function PacketGetAdaptersNPF(): Byte; var LinkageKey, AdapKey, OneAdapKey: HKEY; RegKeySize: DWORD; Status: Longint; i: Integer; dim: DWORD; RegType: DWORD; TName: array[0..255] of AnsiChar; TAName: array[0..255] of AnsiChar; AdapName: array[0..255] of AnsiChar; TcpBindingsMultiString: PAnsiChar; FireWireFlag: UINT; // // Old registry based WinPcap names // // CHAR npfCompleteDriverPrefix[MAX_WINPCAP_KEY_CHARS]; // UINT RegQueryLen; npfCompleteDriverPrefix: array[0..MAX_WINPCAP_KEY_CHARS - 1] of AnsiChar; // = NPF_DRIVER_COMPLETE_DEVICE_PREFIX; DeviceGuidName: array[0..255] of AnsiChar; label tcpip_linkage; begin RegKeySize := 0; FillChar(npfCompleteDriverPrefix, sizeof(npfCompleteDriverPrefix), #0); StrCopy(npfCompleteDriverPrefix, NPF_DRIVER_COMPLETE_DEVICE_PREFIX); //TRACE_ENTER("PacketGetAdaptersNPF"); // // Old registry based WinPcap names // // Get device prefixes from the registry Status := RegOpenKeyEx(HKEY_LOCAL_MACHINE, 'SYSTEMCurrentControlSetControlClass{4D36E972-E325-11CE-BFC1-08002BE10318}', 0, KEY_READ, AdapKey); if (Status <> ERROR_SUCCESS) then begin //TRACE_PRINT("PacketGetAdaptersNPF: RegOpenKeyEx ( Class\{networkclassguid} ) Failed"); goto tcpip_linkage; end; i := 0; //TRACE_PRINT("PacketGetAdaptersNPF: RegOpenKeyEx ( Class\{networkclassguid} ) was successful"); //TRACE_PRINT("PacketGetAdaptersNPF: Cycling through the adapters in the registry:"); // // Cycle through the entries inside the {4D36E972-E325-11CE-BFC1-08002BE10318} key // To get the names of the adapters // //while((Result = RegEnumKey(AdapKey, i, AdapName, sizeof(AdapName)/2)) == ERROR_SUCCESS) while ((RegEnumKey(AdapKey, i, AdapName, sizeof(AdapName) div 2)) = ERROR_SUCCESS) do begin Inc(i); FireWireFlag := 0; // // Get the adapter name from the registry key // Status := RegOpenKeyEx(AdapKey, AdapName, 0, KEY_READ, OneAdapKey); if (Status <> ERROR_SUCCESS) then begin //TRACE_PRINT1("%d) RegOpenKey( OneAdapKey ) Failed, skipping the adapter.",i); continue; end; // // // Check if this is a FireWire adapter, looking for "1394" in its ComponentId string. // We prevent listing FireWire adapters because winpcap can open them, but their interface // with the OS is broken and they can cause blue screens. // dim := sizeof(TName); Status := RegQueryValueEx(OneAdapKey, 'ComponentId', nil, nil, PBYTE(@TName[0]), @dim); if (Status = ERROR_SUCCESS) then begin if (IsFireWire(TName) <> 0) then begin FireWireFlag := INFO_FLAG_DONT_EXPORT; end; end; Status := RegOpenKeyEx(OneAdapKey, 'Linkage', 0, KEY_READ, LinkageKey); if (Status <> ERROR_SUCCESS) then begin RegCloseKey(OneAdapKey); //TRACE_PRINT1("%d) RegOpenKeyEx ( LinkageKey ) Failed, skipping the adapter",i); continue; end; dim := sizeof(DeviceGuidName); Status := RegQueryValueExA(LinkageKey, 'Export', nil, nil, PBYTE(@DeviceGuidName[0]), @dim); if (Status <> ERROR_SUCCESS) then begin RegCloseKey(OneAdapKey); RegCloseKey(LinkageKey); //TRACE_PRINT1("%d) Name = SKIPPED (error reading the key)", i); continue; end; if (strlen(DeviceGuidName) >= strlen('Device')) then begin // Put the DeviceNPF_ string at the beginning of the name StrPCopy(TAName, Format('%s%s', [npfCompleteDriverPrefix, DeviceGuidName + strlen('Device')])); end else continue; //terminate the string, just in case TAName[sizeof(TAName) - 1] := #0; //TRACE_PRINT2("%d) Successfully retrieved info for adapter %s, trying to add it to the global list...", i, TAName); // If the adapter is valid, add it to the list. PacketAddAdapterNPF(TAName, FireWireFlag); RegCloseKey(OneAdapKey); RegCloseKey(LinkageKey); end; // while enum reg keys RegCloseKey(AdapKey); tcpip_linkage: // // no adapters were found under {4D36E972-E325-11CE-BFC1-08002BE10318}. This means with great probability // that we are under Windows NT 4, so we try to look under the tcpip bindings. // //TRACE_PRINT("Adapters not found under SYSTEM\CurrentControlSet\Control\Class. Using the TCP/IP bindings."); Status := RegOpenKeyEx(HKEY_LOCAL_MACHINE, 'SYSTEMCurrentControlSetServicesTcpipLinkage', 0, KEY_READ, LinkageKey); if (Status = ERROR_SUCCESS) then begin // Retrieve the length of th binde key // This key contains the name of the devices as devicefoo //in ASCII, separated by a single '\0'. The list is terminated //by another '\0' Status := RegQueryValueExA(LinkageKey, 'bind', nil, @RegType, nil, @RegKeySize); // Allocate the buffer TcpBindingsMultiString := GlobalAllocPtr(GMEM_MOVEABLE or GMEM_ZEROINIT, RegKeySize + 2); if (TcpBindingsMultiString = nil) then begin //TRACE_PRINT("GlobalAlloc failed allocating memory for the registry key, returning."); //TRACE_EXIT("PacketGetAdaptersNPF"); Result := 0; Exit; end; // Query the key again to get its content Status := RegQueryValueExA(LinkageKey, 'bind', nil, @RegType, PBYTE(@TcpBindingsMultiString[0]), @RegKeySize); RegCloseKey(LinkageKey); // Scan the buffer with the device names i := 0; while True do begin if (TcpBindingsMultiString[i] = #0) then break; StrPCopy(TAName, Format('%s%s', [npfCompleteDriverPrefix, TcpBindingsMultiString + i + strlen('Device')])); // // TODO GV: this cast to avoid a compilation warning is // actually stupid. We shouls check not to go over the buffer boundary! // Inc(i, strlen(PAnsiChar(TcpBindingsMultiString + i)) + 1); // If the adapter is valid, add it to the list. PacketAddAdapterNPF(TAName, 0); end; GlobalFreePtr(TcpBindingsMultiString); end else begin end; Result := 1; end;
另外,IpHlp函数也提供了获取网卡信息的接口,而且网卡名称跟WinPcap的一样。由于IpHlp可以获取网卡的更多信息,例如:IP地址、物理地址、网关IP等信息,所以我们可以结合它来实现更加友好的选择界面。下面是本讲实现的最终效果图:
附件下载:
Snoop2(Jingtao修改版)
本讲演示代码
后面的系列将讲解ARP欺骗、如何实现一个路由器、如何实现一个TCP协议等内容,敬请关注。
分类:网络相关
发表评论
XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>
TrackBack URL | RSS feed for comments on this post.