杀毒软件实时杀毒的奥秘

杀毒软件实时杀毒的奥秘

作者：LuLin

市面上所有号称"虚拟机","防火墙"的实时监控杀毒软件无一不是使用的IFSHOOK技术.但是同时也有一些朋友不断写MAIL给我打听如何实现读写的监控.下面给出用VTOOLSD写的代码.也就是所有实时杀毒软件的奥秘.同时,很多拦截文件操作的软件,例如对目录加密,文件加密等,也采用了雷同的技术.
由于代码十分简单,不分析了.
//=============================================================================
//
//By Lu Lin 2000.5.10
// Apply with VtoolsD 3.01
// DDK version is available if requested.
//Abstract:
// Install a IFS hook, monitoring any read and write access
//
//=============================================================================
// IFSHOOK.c - main module for IFSHOOK

#define　 DEVICE_MAIN
#include　"ifshook.h"
#undef　　DEVICE_MAIN　

//typedef EventHdl(pevent pev,pioreq pir);

typedef struct _Monitored_Files{
struct _Monitored_Files *pNext_Monitored_Files;//pointer to next struct
struct _Monitored_Files *pPre_Monitored_Files;//pointer to previous struct
int sfn;//system file number
int open_count;
char path[260]; //ansi path name
}_Monitored_Files,*pMonitored_Files;

//
//Declare virtual device
//
Declare_Virtual_Device(IFSHOOK)

_Monitored_Files Monitored_Files;
ppIFSFileHookFunc PrevHook;

DefineControlHandler(SYS_VM_INIT, OnSysVMInit);
DefineControlHandler(SYS_DYNAMIC_DEVICE_INIT, OnSysDynamicDeviceInit);
DefineControlHandler(SYS_DYNAMIC_DEVICE_EXIT, OnSysDynamicDeviceExit);
DefineControlHandler(SYS_VM_TERMINATE, OnSysVMTerminate);

PCHAR ConvertPath( int drive, path_t ppath, PCHAR fullpathname )
{
　　int　i = 0;
　　_QWORD　result;

　　//
　　// Stick on the drive letter if we know it.
　　//
　　if( drive != 0xFF ) {

　　　　fullpathname[0] = drive+"A"-1;
　　　　fullpathname[1] = ":";
　　　　i = 2;
　　}
　　UniToBCSPath( &fullpathname[i], ppath->pp_elements, 260 , BCS_WANSI, &result );
　　return( fullpathname );
}

pMonitored_Files IsFileOpened(int i){
pMonitored_Files p=&Monitored_Files;

while (p){
　if (i==p->sfn){
　 return p;
　}
　p=p->pNext_Monitored_Files;
}
return 0;
}

BOOL ControlDispatcher(
DWORD dwControlMessage,
DWORD EBX,
DWORD EDX,
DWORD ESI,
DWORD EDI,
DWORD ECX)
{
START_CONTROL_DISPATCH

　ON_SYS_VM_INIT(OnSysVMInit);
　ON_SYS_DYNAMIC_DEVICE_INIT(OnSysDynamicDeviceInit);
　ON_SYS_DYNAMIC_DEVICE_EXIT(OnSysDynamicDeviceExit);

END_CONTROL_DISPATCH

return TRUE;
}

int _cdecl MyIfsHook(pIFSFunc pfn, int fn, int Drive, int ResType,
　int CodePage, pioreq pir)
{
int retvar,i;
char fullpathname[260];
_Monitored_Files *FileEntry;
switch(fn){
　case IFSFN_OPEN:{
　 retvar=(*PrevHook)(pfn, fn, Drive, ResType, CodePage, pir);
　 ConvertPath( Drive, pir->ir_ppath, fullpathname );
　 FileEntry=IsFileOpened(pir->ir_sfn);
　 if (FileEntry){
　　FileEntry->open_count++;
　 }else{
　　FileEntry=&Monitored_Files;
　　while(1){
　　 if (FileEntry->pNext_Monitored_Files){
　　　FileEntry=FileEntry->pNext_Monitored_Files;
　　 }
　　 else{
　　　break;
　　 }
　　}
　　FileEntry->pNext_Mon_itored_Files=/
　　 HeapAllocate( sizeof(_Monitored_Files),HEAPZEROINIT);
　　FileEntry->pNext_Monitored_Files->pPre_Mon_itored_Files=FileEntry;
　　FileEntry=FileEntry->pNext_Monitored_Files;
　　FileEntry->sfn=pir->ir_sfn;
　　FileEntry->open_count=1;
　　memcpy(FileEntry->path,fullpathname,260);
　 }
　 return retvar;
　}

　case IFSFN_READ:{
　 //Do something here,
　 //eg. Decrypt the file.
　 char *str;
　 int j;
　 str=pir->ir_data;
　 j=pir->ir_length;
　 retvar=(*PrevHook)(pfn, fn, Drive, ResType, CodePage, pir);
　 FileEntry=IsFileOpened(pir->ir_sfn);
　 if (!stricmp("c://test.txt",FileEntry->path)){
　　for (i=0;i<j;i++){
　　 str[i]--;
　　}
　 }
　 return retvar;
　}

　case IFSFN_WRITE:{
　 //Do something here
　 //eg. Encrypt the file
　 FileEntry=IsFileOpened(pir->ir_sfn);
　 if (FileEntry){
　　if (!stricmp("c://test.txt",FileEntry->path)){
　　 for (i=0;i<pir->ir_length;i++){
　　　(((char*)pir->ir_data)[i])++;
　　 }
　　}
　 }
　 return (*PrevHook)(pfn, fn, Drive, ResType, CodePage, pir);
　}

　case IFSFN_CLOSE:{
　 FileEntry=IsFileOpened(pir->ir_sfn);
　 if (FileEntry){　
　　FileEntry->open_count--;
　　if (!FileEntry->open_count){
　　 FileEntry->pPre_Monitored_Files->pNext_Mon_itored_Files=/
　　 FileEntry->pNext_Monitored_Files;
　　 FileEntry->pNext_Monitored_Files->pPre_Mon_itored_Files=/
　　　FileEntry->pPre_Monitored_Files;
　　 HeapFree(FileEntry,0);
　　 }
　 }
　 return (*PrevHook)(pfn, fn, Drive, ResType, CodePage, pir);
　}

}　

return (*PrevHook)(pfn, fn, Drive, ResType, CodePage, pir);
}

BOOL OnSysVMInit(VMHANDLE hVM){
return OnSysDynamicDeviceInit();
}

BOOL OnSysDynamicDeviceInit()
{
PrevHook = IFSMgr_InstallFileSystemApiHook(MyIfsHook);
Monitored_Files.pNext_Mon_itored_Files=0;
Monitored_Files.pPre_Mon_itored_Files=0;
Monitored_Files.sfn=-1;
Monitored_Files.open_count=0;
Monitored_Files.path[0]=0;

return TRUE;
}

BOOL OnSysDynamicDeviceExit()
{
IFSMgr_RemoveFileSystemApiHook(MyIfsHook);
return TRUE;
}

void OnSysVMTerminate(VMHANDLE hVM){
return OnSysDynamicDeviceExit();
}