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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
//application name and version
#define APP_NAME "DNS2SOCKS V1.8"
//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"
//213.73.91.35 for default DNS server supporting TCP (dnscache.berlin.ccc.de)
#define DEFAULT_DNS_SERVER "213.73.91.35"
//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)
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
//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), 0, (struct sockaddr*)&psEntry->client.sAddr, psEntry->uAddrLen);
else
{
//TCP
send(*(SOCKET*)&psEntry->client.hSock, (char*)psEntry->u16aAnswer, ntohs(*psEntry->u16aAnswer)+2, 0);
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);
}
static int InvalidEntryErrorOutput()
{
OutputToLog(OUTPUT_ALL, "Invalid DNS answer detected while calculating TTL");
return 0; //mark as expired for CalculateTimeToLive
}
//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;
int32_t i32TimeToLive;
uint16_t u16ContentLen;
uint16_t u16AmountQuestions;
uint16_t u16Len;
uint8_t* pu8Pos;
uint8_t* pu8AnswerEnd;
uint8_t u8NameLen;
if(psEntry->iTime==(time_t)-1)
return 1; //getting time failed last time; without a working timer we ignore time to live stuff completely
u16Len=ntohs(*psEntry->u16aAnswer);
if(u16Len<=12)
return InvalidEntryErrorOutput(); //answer has no useful information; mark as expired
pu8Pos=(uint8_t*)psEntry->u16aAnswer+2;
pu8AnswerEnd=pu8Pos+u16Len;
u16AmountQuestions=ntohs(((uint16_t*)pu8Pos)[2]);
pu8Pos+=12; //go behind header
//ignore questions
for(; u16AmountQuestions; --u16AmountQuestions)
{
//ignore name
for(;;)
{
if(pu8Pos>=pu8AnswerEnd)
return InvalidEntryErrorOutput(); //failed; mark as expired
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
}
//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);
psEntry->iTime=iCurTime; //store current time for next delivery
//for all records
do
{
//ignore name of resource record
for(;;)
{
if(pu8Pos>=pu8AnswerEnd)
return InvalidEntryErrorOutput(); //failed; mark as expired
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
if(pu8Pos>pu8AnswerEnd-4)
return InvalidEntryErrorOutput(); //failed; mark as expired
//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
if(pu8Pos>pu8AnswerEnd-6)
return InvalidEntryErrorOutput(); //failed; mark as expired
u16ContentLen=ntohs(*(uint16_t*)(pu8Pos+4));
pu8Pos+=6+u16ContentLen;
if(pu8Pos>pu8AnswerEnd)
return InvalidEntryErrorOutput(); //failed; mark as expired
}
while(pu8Pos<pu8AnswerEnd);
return 1; //succeeded, not expired
}
//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;
}
}
}
//thread for connecting the SOCKS server and resolving the DNS request
THREAD_FUNCTION(SocksThread, pEntry)
{
uint16_t u16aBuf[32754]; //max UDP packet length on Windows plus one byte - 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
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;
}
((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, 0);
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, 0);
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, 0);
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;
}
iPos=2+ntohs(*psEntry->u16aRequest);
//send DNS request via SOCKS
iLen=send(hSock, (const char*)psEntry->u16aRequest, iPos, 0);
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);
if(iPos>=iLen)
break; //answer completely received
}
//answer too long?
if(iPos>=sizeof(u16aBuf))
{
OutputToLog(OUTPUT_ALL, "Answer from DNS server too long!");
RemoveEntry(psEntry, hSock, g_bCacheEnabled);
return 0;
}
}
//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
SendAnswer(psEntry);
LeaveCriticalSection(&g_sCritSect);
}
else
{
//send DNS answer to original requesting client via UDP or TCP
psEntry->u16aAnswer=u16aBuf;
SendAnswer(psEntry);
free(psEntry);
}
return 0;
}
//searches the cache for the same request and sends the answer if there is a cache hit
//or creates a thread for forwarding the request to the DNS server via SOCKS
static void HandleDnsRequest(uint16_t* u16aRequest, int iLen, void* pClientAddr, socklen_t iAddrLen)
{
uint8_t* pu8Pos;
uint8_t* pu8End;
struct SEntry* psEntry;
unsigned char uLen;
//search in cache
EnterCriticalSection(&g_sCritSect);
for(psEntry=g_psFirst; ; psEntry=psEntry->psNext)
{
if(!psEntry)
{
//create new entry (length of struct SEntry up to u16aRequest plus request length plus 2 for length)
psEntry=(struct SEntry*)malloc(((uint8_t*)psEntry->u16aRequest-(uint8_t*)psEntry)+iLen+2);
psEntry->iTime=(time_t)-1;
psEntry->u16aAnswer=NULL;
psEntry->uAddrLen=(unsigned char)iAddrLen;
memcpy(&psEntry->client, pClientAddr, iAddrLen);
*psEntry->u16aRequest=htons((uint16_t)iLen);
memcpy(psEntry->u16aRequest+1, u16aRequest, iLen);
//add entry to cache list in case cache is enabled
psEntry->psNext=g_psFirst;
if(g_bCacheEnabled)
g_psFirst=psEntry;
//create thread to resolve entry
if(ThreadCreate(SocksThread, psEntry))
{
++g_uCacheCount;
//output amount of entries and current entry
pu8Pos=(uint8_t*)u16aRequest+12;
pu8End=(uint8_t*)u16aRequest+iLen;
while(pu8Pos<pu8End)
{
uLen=*pu8Pos;
if(!uLen)
{
OutputToLog(OUTPUT_ALL, "%3u %s", g_uCacheCount, (char*)((uint8_t*)u16aRequest+13));
break;
}
if(uLen>=0xc0) //compression used? (reference to other name via offset)
break; //no output in this case
*pu8Pos='.'; //replace length by .
pu8Pos+=uLen+1;
}
}
else
{
//remove entry from cache list
g_psFirst=psEntry->psNext;
free(psEntry);
}
break;
}
//cache hit? (do not compare ID in first 2 bytes of request)
if((uint16_t)iLen==ntohs(*psEntry->u16aRequest) && memcmp(u16aRequest+1, psEntry->u16aRequest+2, iLen-2)==0)
{
//answer already received?
if(psEntry->u16aAnswer)
{
//answer to current address
psEntry->uAddrLen=(unsigned char)iAddrLen;
memcpy(&psEntry->client, pClientAddr, iAddrLen);
//check if expired
if(!CalculateTimeToLive(psEntry))
{
//expired -> kill last answer
free(psEntry->u16aAnswer);
psEntry->u16aAnswer=NULL;
//copy current ID
psEntry->u16aRequest[1]=*u16aRequest;
//create thread to resolve request again
if(!ThreadCreate(SocksThread, psEntry))
RemoveEntry(psEntry, (SOCKET)SOCKET_ERROR, 0);
}
else
{
//use current ID
psEntry->u16aAnswer[1]=*u16aRequest;
SendAnswer(psEntry);
}
}
else
{
//copy current ID so the thread uses that one if it gets the answer
psEntry->u16aRequest[1]=*u16aRequest;
//overwrite address; currently we can only handle one request address while waiting for an answer through SOCKS
//current address is TCP? -> need to close it before overwriting it
if(psEntry->uAddrLen==sizeof(SOCKET))
closesocket(psEntry->client.hSock);
psEntry->uAddrLen=(unsigned char)iAddrLen;
memcpy(&psEntry->client, pClientAddr, iAddrLen);
}
break;
}
}
LeaveCriticalSection(&g_sCritSect);
}
//outputs an error caused by "bind" and closes the according socket
static void OutputBindError(SOCKET hSock, struct sockaddr_storage* psAddr, int bUdp)
{
char szAddr[256];
char szNo[16];
char* szErrMsg=GetSysError(WSAGetLastError());
closesocket(hSock);
if(getnameinfo((struct sockaddr*)psAddr, GetAddrLen(psAddr), szAddr, sizeof(szAddr), szNo, sizeof(szNo), NI_NUMERICHOST|NI_NUMERICSERV))
{
//should never happen
strcpy(szAddr, "unknown address");
strcpy(szNo, "unknown");
}
//UDP is mandatory, TCP is optional
if(bUdp)
{
//need { ... } on *nix as OutputFatal is a multi-line macro there
OutputFatal("\nBinding on %s, UDP port %s has failed: %s\n", szAddr, szNo, szErrMsg);
}
else
OutputToLog(OUTPUT_ALL, "Binding on %s, TCP port %s has failed: %s", szAddr, szNo, szErrMsg);
FreeSysError(szErrMsg);
}
//thread for receiving DNS requests via TCP
THREAD_FUNCTION(TcpThread, pAddr)
{
SOCKET hSockServer;
SOCKET hSock;
uint16_t u16aBuf[32769]; //maximum possible DNS request size plus one byte - using uint16_t here for alignment; the actual size is stored in the first 2 bytes which can have a maximum value of 0xffff
socklen_t iAddrLen;
int iCurBufLen;
int iLen;
uint16_t u16ReqLen;
struct sockaddr_storage sAddr;
char* szErrMsg;
hSockServer=socket(((struct sockaddr_storage*)pAddr)->ss_family, SOCK_STREAM, IPPROTO_TCP);
if(hSockServer==SOCKET_ERROR)
{
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Creating a TCP socket has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
return 0;
}
//bind+listen on local TCP port (get DNS requests)
if(bind(hSockServer, (struct sockaddr*)pAddr, GetAddrLen((struct sockaddr_storage*)pAddr))==SOCKET_ERROR)
{
OutputBindError(hSockServer, (struct sockaddr_storage*)pAddr, 0);
return 0;
}
if(listen(hSockServer, 5)==SOCKET_ERROR)
{
szErrMsg=GetSysError(WSAGetLastError());
closesocket(hSockServer);
OutputToLog(OUTPUT_ALL, "Listening on TCP socket has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
return 0;
}
//as long as "accept" is working
for(;;)
{
iAddrLen=sizeof(sAddr);
hSock=accept(hSockServer, (struct sockaddr*)&sAddr, &iAddrLen);
if(hSock==SOCKET_ERROR)
{
szErrMsg=GetSysError(WSAGetLastError());
OutputToLog(OUTPUT_ALL, "Accepting new connection on TCP socket has failed: %s", szErrMsg);
FreeSysError(szErrMsg);
break;
}
//collect the whole DNS request
iCurBufLen=0;
for(;;)
{
iLen=recv(hSock, (char*)u16aBuf+iCurBufLen, sizeof(u16aBuf)-iCurBufLen, 0);
if(iLen<=0)
{
szErrMsg=GetSysError(WSAGetLastError());
closesocket(hSock);
OutputToLog(OUTPUT_ALL, "DNS request on TCP broken: %s", szErrMsg);
FreeSysError(szErrMsg);
break;
}
iCurBufLen+=iLen;
//got the whole DNS request?
if(iCurBufLen>=2 && (u16ReqLen=ntohs(*u16aBuf))+2>=iCurBufLen)
{
if(u16ReqLen>12) //12 bytes header plus at least one byte of data
HandleDnsRequest(u16aBuf+1, u16ReqLen, &hSock, sizeof(hSock)); //HandleDnsRequest takes care of hSock now
else
closesocket(hSock);
break;
}
}
}
closesocket(hSockServer);
return 0;
}
//parses a command line parameter of the format IPv4 or IPv4:port or IPv6 or [IPv6]:port
static int ParseIpAndPort(int iFlag, const char* szParamName, const char* szPort, char* szIpAndPort, struct sockaddr_storage* psAddr)
{
struct addrinfo sHint;
struct addrinfo* psResult;
char* szPos;
int iRet;
if(strchr(szIpAndPort, '.'))
{
//seems to be IPv4
szPos=strchr(szIpAndPort, ':');
if(szPos)
{
*szPos='\0'; //overwrite ':' for getaddrinfo below
szPort=szPos+1;
}