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DNS2SOCKS.c
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DNS2SOCKS.c
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#include "stdafx.h"
//helpful URLs:
// http://www.networksorcery.com/enp/protocol/dns.htm
// http://www.freesoft.org/CIE/RFC/1035/43.htm
// https://tools.ietf.org/html/rfc2671
// https://tools.ietf.org/html/rfc3225
// https://tools.ietf.org/html/rfc7871
//application name and version
#define APP_NAME "DNS2SOCKS V2.1"
//first output line in console
#define APP_STRING "\n" APP_NAME " (free software, use parameter /? to display help)\n"
//log file header line
#define LOG_HEADER APP_NAME " log opened"
//date/time format string for ISO 8601 format, but leave away the T delimiter as it's bad to read
#define DATE_TIME_FORMAT "%u-%02u-%02u %02u:%02u:%02u "
//127.0.0.1 for default SOCKS5 server
#define DEFAULT_SOCKS_SERVER "127.0.0.1"
//9050 for default SOCKS5 port
#define DEFAULT_SOCKS_PORT "9050"
//46.182.19.48 for default DNS server supporting TCP (Digitalcourage e.V.)
#define DEFAULT_DNS_SERVER "46.182.19.48"
//127.0.0.1 for local IP address for listening
#define DEFAULT_LISTEN_IP "127.0.0.1"
//53 for default DNS port
#define DEFAULT_DNS_PORT "53"
//defines for OutputToLog (bits)
#define OUTPUT_LINE_BREAK (1)
#define OUTPUT_DATE_TIME (2)
#define OUTPUT_CONSOLE (4)
#define OUTPUT_ALL (OUTPUT_LINE_BREAK|OUTPUT_DATE_TIME|OUTPUT_CONSOLE)
//on some systems a failing send command raises a signal; we want to disable that by passing MSG_NOSIGNAL
//some systems (Windows) don't define that -> define it to 0
#ifndef MSG_NOSIGNAL
#define MSG_NOSIGNAL (0)
#endif
union UClient
{
struct sockaddr_storage sAddr; //address of requesting client for UDP
SOCKET hSock; //socket handle for TCP
};
//entry for DNS request and answer (cache entry)
struct SEntry
{
struct SEntry* psNext; //next list entry or NULL
uint16_t* u16aAnswer; //pointer to answer or NULL
time_t iTime; //time when the answer was deliviered last time
union UClient client; //information on how to send response back to client
unsigned char uAddrLen; //length of used part of sAddr for UDP, sizeof(SOCKET) for TCP
uint16_t u16aRequest[1]; //extended dynamically at malloc for "struct SEntry" (use "uint16_t" to ensure according alignment, first element contains length in big endian format)
};
static struct SEntry* g_psFirst=NULL; //list of DNS requests and answers (cache)
static unsigned int g_uCacheCount=0; //amout of entries in list g_psFirst
static int g_bCacheEnabled=1; //!=0 when cache is enabled
static struct sockaddr_storage g_sDnsSrvAddr; //DNS server supporting TCP
static struct sockaddr_storage g_sSocksAddr; //SOCKS5 server
static CRITICAL_SECTION g_sCritSect; //to protect the list g_psFirst and g_uCacheCount
static SOCKET g_hSockUdp; //UDP socket
static unsigned char* g_uaUsrPwd=NULL; //authentication package for SOCKS
static int g_iUsrPwdLen; //length of g_caUsrPwd
static int g_iHttpProxyConnectLen=0; //length of CONNECT command in g_caHttpProxyConnect
static char g_caHttpProxyConnect[300]; //CONNECT command in case of using HTTP proxy
static uint8_t g_u8aEcsOption[8+16]; //EDNS Client Subnet EDNS0 option (maximum necessary bytes reserved, actual amount in g_iEcsOptionLen)
static int g_iEcsOptionLen=0; //actual amount bytes used of g_u8aEcsOption
static int g_bForceEcs=0; //!=0 to replace existing EDNS Client Subnet option by our one
//OS specific functionality
#ifdef _WIN32
//for Windows we can create an own console window, so here we use some OS specific functions;
//also for the file access we use the WIN32 API - we could use the C API as we do for the other OSes
//but as we need to take special care about the line break (\r\n) anyway and WIN32 should be a little
//bit faster, we use WIN32
static HANDLE g_hConsole=NULL; //handle for console output
static HANDLE g_hLogFile=INVALID_HANDLE_VALUE; //handle for log file
//passes a string and its length to a function
#define STRING_AND_LEN(szString) szString, sizeof(szString)-1
static char* GetSysError(int iErrNo)
{
char* szBuffer;
size_t uLen;
if(!FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS, NULL, iErrNo, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&szBuffer, 0, NULL))
{
szBuffer=(char*)LocalAlloc(LMEM_FIXED, 14);
memcpy(szBuffer, "Unknown error", 14);
}
else
{
//remove line breaks at the end
uLen=strlen(szBuffer);
while(uLen>0 && (szBuffer[uLen-1]=='\n' || szBuffer[uLen-1]=='\r'))
szBuffer[--uLen]='\0';
}
return szBuffer;
}
static void FreeSysError(char* szString)
{
LocalFree(szString);
}
static void OutputToLog(unsigned int uOutputSettingBits, const char* szFormatString, ...)
{
va_list pArgs;
int iLenPrefix;
int iLen;
DWORD uDummy;
char szBuf[1024];
//nothing to do?
if((!g_hConsole || !(uOutputSettingBits&OUTPUT_CONSOLE)) && g_hLogFile==INVALID_HANDLE_VALUE)
return;
//add line break?
if(uOutputSettingBits&OUTPUT_LINE_BREAK)
{
szBuf[0]='\r';
szBuf[1]='\n';
iLenPrefix=2;
}
else
iLenPrefix=0;
if(uOutputSettingBits&OUTPUT_DATE_TIME)
{
SYSTEMTIME sTime;
//add date/time string
GetLocalTime(&sTime);
iLen=_snprintf_s(szBuf+iLenPrefix, ARRAYSIZE(szBuf)-iLenPrefix, _TRUNCATE, DATE_TIME_FORMAT, sTime.wYear, sTime.wMonth, sTime.wDay, sTime.wHour, sTime.wMinute, sTime.wSecond);
if(iLen<0) //error?
return;
iLenPrefix+=iLen;
}
//add log string
va_start(pArgs, szFormatString);
iLen=_vsnprintf_s(szBuf+iLenPrefix, ARRAYSIZE(szBuf)-iLenPrefix, _TRUNCATE, szFormatString, pArgs);
if(iLen<0) //error?
return;
iLen+=iLenPrefix;
//output
if(g_hConsole && (uOutputSettingBits&OUTPUT_CONSOLE))
{
wchar_t wcBuf[1024];
//convert to wide char to avoid trouble with special characters
iLen=MultiByteToWideChar(CP_ACP, 0, szBuf, iLen, wcBuf, ARRAYSIZE(wcBuf));
if(iLen)
WriteConsoleW(g_hConsole, wcBuf, iLen, &uDummy, NULL);
}
if(g_hLogFile)
WriteFile(g_hLogFile, szBuf, iLen, &uDummy, NULL);
}
static void OpenLogFile(const char* szFilePath, int bAppend)
{
g_hLogFile=CreateFile(szFilePath, GENERIC_WRITE, FILE_SHARE_READ, NULL, bAppend?OPEN_ALWAYS:CREATE_ALWAYS, 0, NULL);
if(g_hLogFile==INVALID_HANDLE_VALUE)
{
char* szErrMsg=GetSysError(GetLastError());
OutputToLog(OUTPUT_ALL, "Failed to open log file \"%s\": %s", szFilePath, szErrMsg);
FreeSysError(szErrMsg);
}
else
{
//append and no new file was created?
if(bAppend && GetLastError()==ERROR_ALREADY_EXISTS)
{
DWORD uDummy;
//go to end of file for appending
SetFilePointer(g_hLogFile, 0, NULL, FILE_END);
//add line breaks for appending
WriteFile(g_hLogFile, STRING_AND_LEN("\r\n\r\n"), &uDummy, NULL);
}
//output header string in log
OutputToLog(OUTPUT_DATE_TIME, LOG_HEADER);
}
}
static void OpenConsole()
{
if(g_hConsole) //already openend?
return;
AllocConsole();
g_hConsole=GetStdHandle(STD_OUTPUT_HANDLE);
if(g_hConsole)
{
DWORD uDummy;
WriteConsole(g_hConsole, STRING_AND_LEN(APP_STRING), &uDummy, NULL);
}
}
static void OutputFatal(const char* szFormatString, ...)
{
HANDLE hReadConsole;
va_list pArgs;
int iLen;
DWORD uDummy;
INPUT_RECORD sRecord;
char szBuf[4096];
OpenConsole();
if(!g_hConsole) //console available?
return;
va_start(pArgs, szFormatString);
iLen=_vsnprintf_s(szBuf, ARRAYSIZE(szBuf), _TRUNCATE, szFormatString, pArgs);
if(iLen<0) //error?
return;
//output
WriteConsole(g_hConsole, szBuf, iLen, &uDummy, NULL);
WriteConsole(g_hConsole, STRING_AND_LEN("\nPress any key to close the application..."), &uDummy, NULL);
hReadConsole=GetStdHandle(STD_INPUT_HANDLE);
//wait for key
while(ReadConsoleInput(hReadConsole, &sRecord, 1, &uDummy) && (sRecord.EventType!=KEY_EVENT || !sRecord.Event.KeyEvent.bKeyDown))
;
}
//thread handling for Windows
#define THREAD_FUNCTION(threadFunction, pParam) static DWORD __stdcall threadFunction(LPVOID pParam)
int ThreadCreate(LPTHREAD_START_ROUTINE pThreadFunction, void* pParam)
{
DWORD uId;
HANDLE hThread=CreateThread(NULL, 0, pThreadFunction, pParam, 0, &uId);
if(!hThread)
{
char* szErrMsg=GetSysError(GetLastError());
OutputToLog(OUTPUT_ALL, "Creating new thread has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
return 0; //error
}
CloseHandle(hThread);
return 1; //o.k.
}
#else //#ifdef _WIN32
//on other OS create no own console window
static int g_bConsole=0; //console output enabled?
static FILE* g_pLogFile=NULL; //log file pointer
#define GetSysError(iErrNo) strerror(iErrNo)
#define FreeSysError(szString) //nothing to do
static void OutputToLog(unsigned int uOutputSettingBits, const char* szFormatString, ...)
{
va_list pArgs;
int iLenPrefix;
int iLen;
char szBuf[4096];
//nothing to do?
if((!g_bConsole || !(uOutputSettingBits&OUTPUT_CONSOLE)) && !g_pLogFile)
return;
//add line break?
if(uOutputSettingBits&OUTPUT_LINE_BREAK)
{
szBuf[0]='\n';
iLenPrefix=1;
}
else
iLenPrefix=0;
if(uOutputSettingBits&OUTPUT_DATE_TIME)
{
//add date/time string
time_t iTime;
struct tm* psTime;
if(time(&iTime)==(time_t)-1)
return; //error
psTime=localtime(&iTime);
if(!psTime) //error?
return;
iLen=snprintf(szBuf+iLenPrefix, sizeof(szBuf)-iLenPrefix, DATE_TIME_FORMAT, psTime->tm_year+1900, psTime->tm_mon+1, psTime->tm_mday, psTime->tm_hour, psTime->tm_min, psTime->tm_sec);
if(iLen<0) //error?
return;
iLenPrefix+=iLen;
}
//add log string
va_start(pArgs, szFormatString);
iLen=vsnprintf(szBuf+iLenPrefix, sizeof(szBuf)-iLenPrefix, szFormatString, pArgs);
va_end(pArgs);
if(iLen<0) //error?
return;
iLen+=iLenPrefix;
if(iLen>=sizeof(szBuf)) //truncated? -> make sure to add \0
{
szBuf[sizeof(szBuf)-1]='\0';
iLen=sizeof(szBuf)-1;
}
//output
if(g_bConsole && (uOutputSettingBits&OUTPUT_CONSOLE))
fputs(szBuf, stdout);
if(g_pLogFile)
fwrite(szBuf, 1, iLen, g_pLogFile);
}
static void OpenLogFile(const char* szFilePath, int bAppend)
{
g_pLogFile=fopen(szFilePath, bAppend?"ab":"wb");
if(!g_pLogFile)
OutputToLog(OUTPUT_ALL, "Failed to open log file \"%s\": %s", szFilePath, strerror(errno));
else
{
//append and file is not empty?
if(bAppend && ftell(g_pLogFile))
{
//add line breaks for appending
fputs("\n\n", g_pLogFile);
}
setbuf(g_pLogFile, NULL); //disable buffering (no newline needed for actual output)
//output header string in log
OutputToLog(OUTPUT_DATE_TIME, LOG_HEADER);
}
}
static void OpenConsole()
{
if(g_bConsole) //already openend?
return;
g_bConsole=1;
setbuf(stdout, NULL); //disable buffering (no newline needed for actual output)
printf(APP_STRING);
}
//for OutputFatal we can just use a macro to prefix the parameters
#define OutputFatal OpenConsole(); printf
//thread handling via pthread
#define THREAD_FUNCTION(threadFunction, pParam) static void* threadFunction(void* pParam)
int ThreadCreate(void* (*pThreadFunction)(void*), void* pParam)
{
pthread_t hThread;
int iErrNo=pthread_create(&hThread, NULL, pThreadFunction, pParam);
if(iErrNo)
{
OutputToLog(OUTPUT_ALL, "Creating new thread has failed: error code %d", iErrNo);
return 0; //error
}
pthread_detach(hThread);
return 1; //o.k.
}
#endif //#ifdef _WIN32
//returns the internal length of a socket address (IPv4 / IPv6)
static unsigned int GetAddrLen(const struct sockaddr_storage* psAddr)
{
if(psAddr->ss_family==AF_INET)
return sizeof(struct sockaddr_in);
return sizeof(struct sockaddr_in6);
}
//sends UDP answer
static void SendAnswer(struct SEntry* psEntry)
{
//ignore error here
//UDP?
if(psEntry->uAddrLen!=sizeof(SOCKET))
//+2 because DNS on UDP doesn't include the length
sendto(g_hSockUdp, (char*)(psEntry->u16aAnswer+1), ntohs(*psEntry->u16aAnswer), MSG_NOSIGNAL, (struct sockaddr*)&psEntry->client.sAddr, psEntry->uAddrLen);
else
{
//TCP
send(*(SOCKET*)&psEntry->client.hSock, (char*)psEntry->u16aAnswer, ntohs(*psEntry->u16aAnswer)+2, MSG_NOSIGNAL);
closesocket(psEntry->client.hSock);
}
}
//searches for an entry in the cache list and removes it - also closes a socket and outputs an error message
static void RemoveEntry(struct SEntry* psEntry, SOCKET hSock, int bUseCriticalSection)
{
struct SEntry** ppsPrev;
struct SEntry* psEntry2;
//close the socket created by the caller
if(hSock!=SOCKET_ERROR)
closesocket(hSock);
if(bUseCriticalSection)
EnterCriticalSection(&g_sCritSect);
ppsPrev=&g_psFirst;
for(psEntry2=g_psFirst; psEntry2; psEntry2=psEntry2->psNext)
{
//found entry?
if(psEntry==psEntry2)
{
//remove entry from list
*ppsPrev=psEntry->psNext;
--g_uCacheCount;
break;
}
ppsPrev=&psEntry2->psNext;
}
//free the entry
free(psEntry->u16aAnswer); //should be NULL anyway
//close socket in case of TCP
if(psEntry->uAddrLen==sizeof(SOCKET))
closesocket(psEntry->client.hSock);
free(psEntry);
if(bUseCriticalSection)
LeaveCriticalSection(&g_sCritSect);
}
//outputs error for TTL check (i32TimeOffset>=0) or searching OPT pseudo-RR (i32TimeOffset<0)
static int InvalidDnsMsgErrorOutput(int32_t i32TimeOffset)
{
if(i32TimeOffset>=0)
OutputToLog(OUTPUT_ALL, "Invalid DNS answer detected while calculating TTL");
else
OutputToLog(OUTPUT_ALL, "Invalid DNS requested detected while searching OPT pseudo-RR");
return 0; //error
}
//iterates through DNS message parts
//either to update/check TTL (i32TimeOffset>=0) or to find OPT pseudo-RR (i32TimeOffset<0)
//returns 0 on error/TTL expiration, 1 on success or offset of OPT pseudo-RR
static int IterateDnsMessage(uint16_t* u16aMessage, int32_t i32TimeOffset)
{
int32_t i32TimeToLive;
uint16_t u16ContentLen;
uint16_t u16AmountQuestions;
uint16_t u16Len;
uint8_t* pu8Pos;
uint8_t* pu8MessageEnd;
uint8_t u8NameLen;
u16Len=ntohs(*u16aMessage);
if(u16Len<=12)
return InvalidDnsMsgErrorOutput(i32TimeOffset); //answer has no useful information
pu8Pos=(uint8_t*)u16aMessage+2;
pu8MessageEnd=pu8Pos+u16Len;
u16AmountQuestions=ntohs(((uint16_t*)pu8Pos)[2]);
pu8Pos+=12; //go behind header
//ignore questions
for(; u16AmountQuestions; --u16AmountQuestions)
{
//ignore name
for(;;)
{
if(pu8Pos>=pu8MessageEnd)
return InvalidDnsMsgErrorOutput(i32TimeOffset); //failed
u8NameLen=*pu8Pos;
if(!u8NameLen)
break; //end of name
if(u8NameLen>=0xc0) //compression used? (reference to other name via offset)
{
++pu8Pos; //ignore 2nd part of offset
break;
}
pu8Pos+=u8NameLen+1;
}
pu8Pos+=5; //ignore type and class
}
//for finding OPT pseudo-RR the DNS request might end after the questions
if(i32TimeOffset<0 && pu8Pos==pu8MessageEnd)
return 1; //found no OPT pseudo-RR
//for all records
do
{
//ignore name of resource record
for(;;)
{
if(pu8Pos>=pu8MessageEnd)
return InvalidDnsMsgErrorOutput(i32TimeOffset); //failed
u8NameLen=*pu8Pos;
if(!u8NameLen)
break; //end of name
if(u8NameLen>=0xc0) //compression used? (reference to other name via offset)
{
++pu8Pos; //ignore 2nd part of offset
break;
}
pu8Pos+=u8NameLen+1;
}
pu8Pos+=5; //jump behind type and class
if(pu8Pos>pu8MessageEnd-6) //6: TTL + RDLEN
return InvalidDnsMsgErrorOutput(i32TimeOffset); //failed
//type is OPT pseudo-RR which has no real TTL value?
if(ntohs(*(uint16_t*)(pu8Pos-4))==41)
{
//searching OPT pseudo-RR?
if(i32TimeOffset<0)
return (int)((pu8Pos+6)-(uint8_t*)u16aMessage); //return offset to data
}
else if(i32TimeOffset>=0)
{
//check time to live field (0 means "omitted")
i32TimeToLive=ntohl(*(uint32_t*)pu8Pos);
if(i32TimeToLive>0)
{
i32TimeToLive-=i32TimeOffset;
if(i32TimeToLive<=0)
return 0; //expired
*(uint32_t*)pu8Pos=htonl(i32TimeToLive); //update field
}
else if(i32TimeToLive<0)
return 0; //failed, TTL must be positive; mark as expired, however: no error output in this case
}
//ignore record content
u16ContentLen=ntohs(*(uint16_t*)(pu8Pos+4));
pu8Pos+=6+u16ContentLen;
if(pu8Pos>pu8MessageEnd)
return InvalidDnsMsgErrorOutput(i32TimeOffset); //failed
}
while(pu8Pos<pu8MessageEnd);
return 1; //succeeded
}
//updates the time to live fields of an entry and checks for expiration (returns 0 if expired)
static int CalculateTimeToLive(struct SEntry* psEntry)
{
time_t iCurTime;
int32_t i32TimeOffset;
if(psEntry->iTime==(time_t)-1)
return 1; //getting time failed last time; without a working timer we ignore time to live stuff completely
//calculate amount of seconds since last delivery
if(time(&iCurTime)==(time_t)-1)
return 1; //error, can't get current time -> ignore time to live stuff completely
i32TimeOffset=(int32_t)(iCurTime-psEntry->iTime);
if(i32TimeOffset<0)
return 0; //time increased; overflow? Mark as expired
psEntry->iTime=iCurTime; //store current time for next delivery
return IterateDnsMessage(psEntry->u16aAnswer, i32TimeOffset);
}
//receives a specific amount of bytes
static int ReceiveBytes(SOCKET hSock, unsigned int uAmount, uint16_t* u16aBuf)
{
unsigned int uPos=0;
int iLen;
char* szErrMsg;
for(;;)
{
iLen=recv(hSock, (char*)u16aBuf+uPos, uAmount, 0);
switch(iLen)
{
case SOCKET_ERROR:
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Receiving from SOCKS server has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
return 0; //failed
case 0:
OutputToLog(OUTPUT_ALL, "The SOCKS server has closed the connection unexpectedly");
return 0; //failed
default:
uAmount-=iLen;
if(!uAmount)
return 1; //succeeded
uPos+=iLen;
}
}
}
//for sending DNS requests where we add/manipulate the ECS option
//returns 0 on error, -1 to send original message or the new message length otherwise
static int AddEcsOption(uint16_t* u16aRequest, uint16_t* u16aDestBuf)
{
//try to find OPT pseudo-RR
int iOffset=IterateDnsMessage(u16aRequest, -1);
switch(iOffset)
{
case 0: //error
return 0;
case 1: //no OPT pseudo-RR
{
//add it
uint16_t u16Len=ntohs(*(uint16_t*)u16aRequest);
uint32_t u32NewLen=u16Len+g_iEcsOptionLen+11;
uint8_t* u8aDest;
//new length exceeds maximum?
if(u32NewLen>65535)
{
OutputToLog(OUTPUT_ALL, "Cannot add EDNS client subnet info to DNS request as it would exceed the maximum size");
return 0;
}
//create new DNS request; starts with length as we use TCP
*u16aDestBuf=htons((uint16_t)u32NewLen);
memcpy(u16aDestBuf+1, u16aRequest+1, u16Len); //copy original request
u16aDestBuf[6]=htons(ntohs(u16aDestBuf[6])+1); //increase "additional count"
u8aDest=((uint8_t*)(u16aDestBuf+1))+u16Len; //jump after original message
//add OPT pseudo-RR
u8aDest[0]=0; //name -> empty
u8aDest[1]=0;
u8aDest[2]=41; //type -> OPT pseudo-RR
u8aDest[3]=0x10;//max UDP size: 4096
u8aDest[4]=0;
*(uint32_t*)(u8aDest+5)=0; //TTL (here: extended RCODE and flags -> all 0 -> no DNSSEC)
*(uint16_t*)(u8aDest+9)=htons((uint16_t)g_iEcsOptionLen); //option length
memcpy(u8aDest+11, g_u8aEcsOption, g_iEcsOptionLen); //add option
return (int)(u32NewLen+2); //+2 for length field
}
default: //found OPT pseudo-RR
{
//try to find EDNS Client Subnet option
uint8_t* pu8Pos=((uint8_t*)u16aRequest)+iOffset; //offset points to option data
uint16_t u16OptLen=ntohs(((uint16_t*)pu8Pos)[-1]); //length before data
uint8_t* pu8OptionsEnd=pu8Pos+u16OptLen;
uint16_t u16Len=ntohs(*(uint16_t*)u16aRequest);
uint8_t* pu8MessageEnd=((uint8_t*)u16aRequest)+2+u16Len;
uint16_t u16LenIncludingOptionsToCopy;
uint16_t u16CurOptLen;
uint32_t u32NewLen;
//pu8OptionsEnd beyond end of message? -> error
if(pu8OptionsEnd>pu8MessageEnd)
return InvalidDnsMsgErrorOutput(-1);
for(;; pu8Pos+=u16CurOptLen)
{
if(pu8Pos>=pu8OptionsEnd)
{
//no EDNS Client Subnet option -> add it
break;
}
u16CurOptLen=ntohs(*(uint16_t*)(pu8Pos+2))+4;
if(u16CurOptLen<4 || pu8Pos>pu8OptionsEnd-u16CurOptLen) //overflow or beyond end of message?
return InvalidDnsMsgErrorOutput(-1); //failed
//EDNS Client Subnet option?
if(ntohs(*(uint16_t*)pu8Pos)==8)
{
if(!g_bForceEcs)
return -1; //special return value to send original DNS message as we shall not replace ECS
//replace existing option
//correct parameters for lower message creation
pu8OptionsEnd=pu8Pos+u16CurOptLen; //behind EDNS Client Subnet option
u16OptLen-=u16CurOptLen;
u16Len-=u16CurOptLen;
break;
}
}
u32NewLen=u16Len+g_iEcsOptionLen;
//new length exceeds maximum?
if(u32NewLen>65535)
{
OutputToLog(OUTPUT_ALL, "Cannot add EDNS client subnet info to DNS request as it would exceed the maximum size");
return 0;
}
*u16aDestBuf=htons((uint16_t)u32NewLen);
u16LenIncludingOptionsToCopy=(uint16_t)(pu8Pos-(uint8_t*)u16aRequest);
memcpy(u16aDestBuf+1, u16aRequest+1, u16LenIncludingOptionsToCopy-2); //copy part of original request without length field
memcpy(((uint8_t*)u16aDestBuf)+u16LenIncludingOptionsToCopy, g_u8aEcsOption, g_iEcsOptionLen); //add ECS option
memcpy(((uint8_t*)u16aDestBuf)+u16LenIncludingOptionsToCopy+g_iEcsOptionLen, pu8OptionsEnd, pu8MessageEnd-pu8OptionsEnd); //copy rest of original message
//correct length of options
*(uint16_t*)(((uint8_t*)u16aDestBuf)+iOffset-2)=htons((uint16_t)(u16OptLen+g_iEcsOptionLen));
return (int)(u32NewLen+2); //+2 for length field
}
}
}
//sends CONNECT command to HTTP proxy and checks answer
static int HandleHttpProxy(SOCKET hSock, char* caBuf)
{
char* szErrMsg;
char* szPosEnd;
const char* szPosStatus;
int iRet;
int iPos;
iRet=send(hSock, g_caHttpProxyConnect, g_iHttpProxyConnectLen, MSG_NOSIGNAL);
if(iRet!=g_iHttpProxyConnectLen)
{
szErrMsg=(iRet==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Invalid amount of sent bytes";
OutputToLog(OUTPUT_ALL, "Sending to HTTP proxy has failed: %s", szErrMsg);
if(iRet==SOCKET_ERROR)
FreeSysError(szErrMsg);
return 0; //error
}
//receive answer
iPos=0;
for(;;)
{
iRet=recv(hSock, caBuf+iPos, 2000-iPos, 0);
if(iRet<=0)
{
if(iRet==SOCKET_ERROR)
OutputToLog(OUTPUT_ALL, "The HTTP proxy has closed the connection unexpectedly");
else
{
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Receiving from HTTP proxy has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
}
return 0; //error
}
iPos+=iRet;
if(iPos<4)
continue; //continue receiving
//check header, must begin with HTTP
if(caBuf[0]=='H' || caBuf[1]=='T' || caBuf[2]=='T' || caBuf[3]=='P')
{
caBuf[iPos]='\0'; //terminate the string
//try to find empty line that marks the end of the HTTP proxy answer
szPosEnd=strstr(caBuf, "\r\n\r\n");
if(!szPosEnd)
continue; //continue receiving
//extract status code -> scan for space character (also stops on any control character)
szPosStatus=caBuf+4;
while(*(unsigned char*)szPosStatus>' ')
++szPosStatus;
if(*szPosStatus==' ')
{
//we want: 200 Connection established
if(atoi(++szPosStatus)==200)
break; //header reception complete
//find end of line (must be there, otherwise upper search for empty line would have failed
szPosEnd=strchr(szPosStatus, '\r');
*szPosEnd='\0';
OutputToLog(OUTPUT_ALL, "Connecting DNS server has failed: %s", szPosStatus);
return 0; //error
}
}
OutputToLog(OUTPUT_ALL, "Invalid answer from HTTP proxy");
return 0; //error
}
//so far there shouldn't be an answer from the DNS server (nothing after \r\n\r\n)
if(szPosEnd[4])
{
OutputToLog(OUTPUT_ALL, "DNS server answered before request");
return 0; //error
}
return 1; //o.k.
}
//thread for connecting the SOCKS server and resolving the DNS request
THREAD_FUNCTION(DnsThread, pEntry)
{
uint16_t u16aBuf[32769]; //max DNS packet length 2(length)+65535(data) bytes - using uint16_t here for alignment
struct SEntry* psEntry=(struct SEntry*)pEntry;
char* szErrMsg;
SOCKET hSock=socket(g_sSocksAddr.ss_family, SOCK_STREAM, IPPROTO_TCP);
int iRet;
int iPos;
int iLen;
if(hSock==SOCKET_ERROR)
{
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Creating a TCP socket has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//connect SOCKS server or HTTP proxy
if(connect(hSock, (struct sockaddr*)&g_sSocksAddr, GetAddrLen(&g_sSocksAddr))==SOCKET_ERROR)
{
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Connecting the SOCKS server has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//using HTTP proxy instead of SOCKS?
if(g_iHttpProxyConnectLen)
{
if(!HandleHttpProxy(hSock, (char*)u16aBuf))
{
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
}
else
{
((uint8_t*)u16aBuf)[0]=5; //version 5 as we use SOCKS5
((uint8_t*)u16aBuf)[1]=1; //number of authentication methods supported
((uint8_t*)u16aBuf)[2]=g_uaUsrPwd?2:0; //user/password authentication or no authentication
iLen=send(hSock, (const char*)u16aBuf, 3, MSG_NOSIGNAL);
if(iLen!=3)
{
szErrMsg=(iLen==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Invalid amount of sent bytes";
OutputToLog(OUTPUT_ALL, "Sending to SOCKS server has failed: %s", szErrMsg);
if(iLen==SOCKET_ERROR)
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//check respons
if(!ReceiveBytes(hSock, 2, u16aBuf+8))
{
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
if(((uint8_t*)u16aBuf)[16]!=5 || ((uint8_t*)u16aBuf)[17]!=((uint8_t*)u16aBuf)[2])
{
if(((uint8_t*)u16aBuf)[16]!=5)
OutputToLog(OUTPUT_ALL, "The SOCKS server has answered with a SOCKS version number unequal to 5");
else if(g_uaUsrPwd)
OutputToLog(OUTPUT_ALL, "The SOCKS server does not support user/password authentication");
else
OutputToLog(OUTPUT_ALL, "The SOCKS server wants an authentication");
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//send authentication if enabled
if(g_uaUsrPwd)
{
iLen=send(hSock, (const char*)g_uaUsrPwd, g_iUsrPwdLen, MSG_NOSIGNAL);
if(iLen!=g_iUsrPwdLen)
{
szErrMsg=(iLen==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Invalid amount of sent bytes";
OutputToLog(OUTPUT_ALL, "Sending to SOCKS server has failed: %s", szErrMsg);
if(iLen==SOCKET_ERROR)
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//check response
if(!ReceiveBytes(hSock, 2, u16aBuf+8))
{
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
if(((uint8_t*)u16aBuf)[17]) //2nd byte of answer must be 0 for "success"
{
OutputToLog(OUTPUT_ALL, "The SOCKS server authentication has failed (error code %u)", (unsigned int)((uint8_t*)u16aBuf)[17]);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
}
//connect DNS server via SOCKS, the DNS server must support TCP
((uint8_t*)u16aBuf)[1]=1; //establish a TCP/IP stream connection
((uint8_t*)u16aBuf)[2]=0; //reserved, must be 0x00
switch(g_sDnsSrvAddr.ss_family)
{
case AF_UNSPEC: //use name
((uint8_t*)u16aBuf)[3]=3; //name
iLen=(int)((struct sockaddr_in6*)&g_sDnsSrvAddr)->sin6_flowinfo; //length in sin6_flowinfo (see ParseIpAndPort)
((uint8_t*)u16aBuf)[4]=(uint8_t)iLen; //maximum length is 255
memcpy(((uint8_t*)u16aBuf)+5, *(char**)&((struct sockaddr_in6*)&g_sDnsSrvAddr)->sin6_addr, iLen); //copy name (see ParseIpAndPort)
*(uint16_t*)(((uint8_t*)u16aBuf)+iLen+5)=((struct sockaddr_in6*)&g_sDnsSrvAddr)->sin6_port; //port
iPos=iLen+7;
break;
case AF_INET: //use IPv4
((uint8_t*)u16aBuf)[3]=1; //IPv4 address
*(uint32_t*)(u16aBuf+2)=((struct sockaddr_in*)&g_sDnsSrvAddr)->sin_addr.s_addr; //address
*(uint16_t*)(u16aBuf+4)=((struct sockaddr_in*)&g_sDnsSrvAddr)->sin_port; //port
iPos=10;
break;
default: //use IPv6
((uint8_t*)u16aBuf)[3]=4; //IPv6 address
memcpy(u16aBuf+2, &((struct sockaddr_in6*)&g_sDnsSrvAddr)->sin6_addr, 16); //address
*(uint16_t*)(u16aBuf+10)=((struct sockaddr_in6*)&g_sDnsSrvAddr)->sin6_port; //port
iPos=22;
}
iLen=send(hSock, (const char*)u16aBuf, iPos, MSG_NOSIGNAL);
if(iLen!=iPos)
{
szErrMsg=(iLen==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Invalid amount of sent bytes";
OutputToLog(OUTPUT_ALL, "Connecting through SOCKS server has failed: %s", szErrMsg);
if(iLen==SOCKET_ERROR)
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//check expected answer (get first 5 bytes to detect address type)
if(!ReceiveBytes(hSock, 5, u16aBuf))
{
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
if(((uint8_t*)u16aBuf)[0]!=5 || ((uint8_t*)u16aBuf)[1]!=0 || (((uint8_t*)u16aBuf)[3]!=1 && ((uint8_t*)u16aBuf)[3]!=3 && ((uint8_t*)u16aBuf)[3]!=4))
{
szErrMsg="Unexpected answer from SOCKS server";
//correct version -> try to resolve the error code
if(((uint8_t*)u16aBuf)[0]==5)
switch(((uint8_t*)u16aBuf)[1])
{
case 2:
szErrMsg="Connection not allowed by ruleset";
break;
case 3:
szErrMsg="Network unreachable";
break;
case 4:
szErrMsg="Host unreachable";
break;
case 5:
szErrMsg="Connection refused by destination host";
break;
case 6:
szErrMsg="TTL expired";
break;
case 7:
szErrMsg="Command not supported / protocol error";
break;
case 8:
szErrMsg="Address type not supported";
}
OutputToLog(OUTPUT_ALL, "Connecting through SOCKS server has failed: %s", szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//get rest of answer
//all bytes after that are part of the "normal" communication
switch(((uint8_t*)u16aBuf)[3])
{
case 1: //IPv4
iLen=5;
break;
case 4: //IPv6
iLen=17;
break;
default: //name
iLen=2+((uint8_t*)u16aBuf)[4]; //port length plus length of name
}
if(!ReceiveBytes(hSock, iLen, u16aBuf))
{
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
}
//send DNS request via SOCKS; TCP variant starts with 2 byte length field
//add ECS?
if(g_iEcsOptionLen)
iPos=AddEcsOption(psEntry->u16aRequest, u16aBuf);
else
iPos=-1; //no ECS -> send original message
switch(iPos)
{
case 0: //error
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
case -1: //send original message
iPos=2+ntohs(*psEntry->u16aRequest);
iLen=send(hSock, (const char*)psEntry->u16aRequest, iPos, MSG_NOSIGNAL);
break;
default: //send message created by AddEcsOption
iLen=send(hSock, (const char*)u16aBuf, iPos, MSG_NOSIGNAL);
}
//error or not sent all bytes?
if(iLen!=iPos)
{
szErrMsg=(iLen==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Invalid amount of sent bytes";
OutputToLog(OUTPUT_ALL, "Sending through SOCKS server has failed: %s", szErrMsg);
if(iLen==SOCKET_ERROR)
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
//receive answer
iPos=0;
for(;;)
{
iRet=recv(hSock, (char*)u16aBuf+iPos, sizeof(u16aBuf)-iPos, 0);
if(iRet<=0)
{
szErrMsg=(iRet==SOCKET_ERROR)?GetSysError(WSAGetLastError()):"Server has closed the connection unexpectedly";
OutputToLog(OUTPUT_ALL, "Broken answer from DNS server: %s", szErrMsg);
if(iRet==SOCKET_ERROR)
FreeSysError(szErrMsg);
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
iPos+=iRet;
//first 2 bytes contain length (Big Endian)
if(iPos>=2)
{
iLen=2+ntohs(*u16aBuf); //iLen maximum is 2+65535 (smaller than sizeof(u16aBuf))
if(iPos>=iLen)
break; //answer completely received
}
}
//invalid answer?
if(iPos<=4)
{
OutputToLog(OUTPUT_ALL, "Answer from DNS server too short!");
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
closesocket(hSock);
if(g_bCacheEnabled)
{
//store answer in cache
EnterCriticalSection(&g_sCritSect);
psEntry->u16aAnswer=(uint16_t*)malloc(iLen);
memcpy(psEntry->u16aAnswer, u16aBuf, iLen);
//copy ID
psEntry->u16aAnswer[1]=psEntry->u16aRequest[1];
//remember current time for time to live calculations
psEntry->iTime=time(NULL);
//send DNS answer to original requesting client via UDP or TCP