webresponsemodifier.rar

/*++ Copyright (c) Microsoft Corporation. All rights reserved. THIS CODE IS MADE AVAILABLE AS IS, WITHOUT WARRANTY OF ANY KIND. THE ENTIRE RISK OF THE USE OR THE RESULTS FROM THE USE OF THIS CODE REMAINS WITH THE USER. USE AND REDISTRIBUTION OF THIS CODE, WITH OR WITHOUT MODIFICATION, IS HEREBY PERMITTED. --*/ /* * * This filter is a flavor of the filter IIS uses for compression. * (Original filter written by David Treadwell on July 1997.) * * ISA and IIS let you accumulate Requests chunks into a complete * Request. * The following filter is an example to a filter that collects the * response chunks and then allows you to change them depending on the * complete response. * This filter works with 2 notifications. * In Send Raw Data it collects the response's chunks, sends 0 bytes * instead of them (i.e. sends nothing). * Then, when all the chunks of this response passed Send Raw Data * notification, ISA thinks the complete response was sent. So * it calls End Of Request Notification. End Of Request Notification * will be the place where we will send the complete response. * * Note. Since the filter allocates memory for accumulating a response from a * Web server, it is vulnerable to a DoS attack. In this sample we show how * to handle that issue using a threshold. When the memory needed for the * response exceeds that threshold, the filter will behave as if it received * an end-of-request notification and will call OnEndOfRequest. The * OnEndOfRequest function will try do to change the response based on the * partial data accumulated. After doing this, the filter will notify the * ISA Server Web proxy to stop sending notifications regarding the current * request. After this, the filter will transparent and pass the response * without altering it. */ #include <WINDOWS.H> #include <HTTPFILT.H> #include <STDIO.H> #include <STDLIB.H> #include <ERRNO.H> #include <LIMITS.H> #include <ASSERT.H> #include <STRSAFE.H> #include <SALANNOTATIONS.H> #define CONTENTLEN_SIZE 100 #define SIZEOF_CHAR (sizeof(' ')) #define STRING_SIZE(str) (sizeof(str) - 1) const char LINE_TO_INSERT[] = "<H3>Brought to you by an ISA Web Filter</H3>/r/n"; const char CONTENT_LENGTH[] = "Content-Length:"; const int ACCUMULATION_SIZE_LIMIT = 10000; static DWORD OnSendRawData(PHTTP_FILTER_CONTEXT pfc, PHTTP_FILTER_RAW_DATA pRawData); static DWORD OnEndOfRequest(PHTTP_FILTER_CONTEXT pfc); static void DisableNotifications(PHTTP_FILTER_CONTEXT pfc, DWORD flags); static int strnstr(const char *string, const char *strCharSet , int n); void OutputDebugStringF (const char* pchFormat, ...); static bool InsertOurHTMLHeader(PHTTP_FILTER_CONTEXT pfc,LPBYTE *ppBuffer,LPDWORD lpdwLen); static DWORD dwfnContentLen(__in LPSTR ContentLenLine,int iLineLen); static DWORD IsFirstInCARP(PHTTP_FILTER_CONTEXT pfc, BOOL *IsFirst); BOOL WINAPI TerminateFilter ( DWORD dwFlags ) { UNREFERENCED_PARAMETER(dwFlags); return TRUE; } BOOL WINAPI GetFilterVersion ( PHTTP_FILTER_VERSION pVer ) { if (pVer == NULL) { SetLastError( ERROR_INVALID_PARAMETER); return FALSE; } pVer->dwFilterVersion = HTTP_FILTER_REVISION; pVer->dwFlags = SF_NOTIFY_ORDER_HIGH | SF_NOTIFY_SECURE_PORT | SF_NOTIFY_NONSECURE_PORT | SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA ; return TRUE; } DWORD WINAPI HttpFilterProc ( PHTTP_FILTER_CONTEXT pfc, DWORD NotificationType,__inout LPVOID pvNotification ) { OutputDebugStringA("WEBRESPONSEMODIFIER: entring HttpFilterProc./n"); DWORD dwRet = SF_STATUS_REQ_NEXT_NOTIFICATION; switch (NotificationType) { case SF_NOTIFY_SEND_RAW_DATA: dwRet = OnSendRawData(pfc, (PHTTP_FILTER_RAW_DATA)pvNotification); break; case SF_NOTIFY_END_OF_REQUEST: dwRet = OnEndOfRequest(pfc); break; default: // We cannot reach here, unless Web Filter support has a BAD ERROR. SetLastError( ERROR_INVALID_PARAMETER); dwRet = SF_STATUS_REQ_ERROR; break; } return dwRet; } /* * OnSendRawData(): * During Send Raw Data Notification we do the following: * 1) Append each chunk to an accumulation buffer (pRawData->cvInData). * 2) Resize the Current chunk to 0 (don't send anything.) */ static DWORD OnSendRawData ( PHTTP_FILTER_CONTEXT pfc, PHTTP_FILTER_RAW_DATA pInRawData ) { if ( NULL == pfc || NULL == pInRawData) { SetLastError( ERROR_INVALID_PARAMETER); return SF_STATUS_REQ_ERROR; } /* * Making the filter CARP-aware. * The filter is active only if we are in the last array server. */ BOOL IsFirst; DWORD dwErrorCode = IsFirstInCARP(pfc,&IsFirst) ; if (dwErrorCode != ERROR_SUCCESS) { SetLastError(dwErrorCode); return SF_STATUS_REQ_ERROR; } if (!IsFirst) { OutputDebugStringA("WEBRESPONSEMODIFIER: OnSendRawData, intra array server, do nothing./n"); DisableNotifications(pfc, SF_NOTIFY_SEND_RAW_DATA); return SF_STATUS_REQ_NEXT_NOTIFICATION; } OutputDebugStringA("WEBRESPONSEMODIFIER: First array server, accumulate data./n"); /* * Called first time for this request - then allocate pRawData. */ DWORD dwReserved = 0; if ( NULL == pfc->pFilterContext ) { pfc->pFilterContext = (LPVOID)pfc->AllocMem( pfc, sizeof(HTTP_FILTER_RAW_DATA), dwReserved); if ( NULL == pfc->pFilterContext ) { DisableNotifications( pfc, SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); SetLastError( ERROR_NOT_ENOUGH_MEMORY ); return SF_STATUS_REQ_ERROR; } PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext; pRawData->cbInBuffer = pInRawData->cbInBuffer; pRawData->pvInData = (LPVOID)pfc->AllocMem( pfc, pRawData->cbInBuffer, dwReserved); if ( NULL == pRawData->pvInData ) { DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); SetLastError( ERROR_NOT_ENOUGH_MEMORY ); return SF_STATUS_REQ_ERROR; } pRawData->cbInData = 0; pRawData->dwReserved = pInRawData->dwReserved ; } /* * Get the pRawData from the Request Context. */ PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext; /* * Check for integer overflow */ DWORD NewSize = pInRawData->cbInData + pRawData->cbInData ; if (NewSize < pInRawData->cbInData || NewSize < pRawData->cbInData ) { DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); SetLastError( ERROR_NOT_ENOUGH_MEMORY ); return SF_STATUS_REQ_ERROR; } OutputDebugStringF("WEBRESPONSEMODIFIER: new data size: %d./n",NewSize); /* * Check if the memory needed exceeds the limit allowed (the threshold). * Note. In this sample, when the filter identifies such a case, it will try to * change the response based on the partial data accumulated. After that, * the filter will cease to receive notifications for the current request and * will pass the rest of the response without change. This sample can be * modified so that the filter will block the response if the threshold is * exceeded. */ if (NewSize > ACCUMULATION_SIZE_LIMIT) { OutputDebugStringF("WEBRESPONSEMODIFIER: OnSendRawData, required data size (%d) exceeds accumulation limit (%d) - trying to insert header./n",NewSize,ACCUMULATION_SIZE_LIMIT); DWORD dwRetVal = OnEndOfRequest(pfc); DisableNotifications( pfc, SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); return dwRetVal; } /* * If the buffer in pRawData is insufficient, increase the buffer size. * Note. To achieve better performance, when additional memory allocation * is needed, the filter allocates twice the amount of memory that is needed. * This way, we reduce the number of allocation operations significantly and * achieve better performance for the filter. */ if ( NewSize > pRawData->cbInBuffer) { /* * Check for integer overflow */ pRawData->cbInBuffer = 2*NewSize; if (pRawData->cbInBuffer < NewSize) { DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); SetLastError( ERROR_ARITHMETIC_OVERFLOW ); return SF_STATUS_REQ_ERROR; } LPBYTE lpBuffer = (LPBYTE)pfc->AllocMem(pfc,pRawData->cbInBuffer, dwReserved); if ( NULL == lpBuffer ) { DisableNotifications(pfc,SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); SetLastError( ERROR_NOT_ENOUGH_MEMORY ); return SF_STATUS_REQ_ERROR; } memcpy((LPVOID)lpBuffer, pRawData->pvInData, pRawData->cbInData); pRawData->pvInData = (void *)lpBuffer; } /* * Append InRawData ( new chunk ) to accumulation buffer. */ LPBYTE lpBuffer = (LPBYTE)pRawData->pvInData; memcpy((LPVOID)(&lpBuffer[pRawData->cbInData]), pInRawData->pvInData, pInRawData->cbInData); pRawData->cbInData = pRawData->cbInData + pInRawData->cbInData; /* * Mark current chunk as size 0 ( i.e. Don't send enything. ) */ pInRawData->cbInData = 0; return SF_STATUS_REQ_NEXT_NOTIFICATION; } /* * OnEndOfRequest(): * During End Of Request Notification we: * 1) Get the complete response from the filter Request Specific Data. * 2) May manipulate that response. * 3) Send that response. */ static DWORD OnEndOfRequest ( PHTTP_FILTER_CONTEXT pfc ) { if ( NULL == pfc) { SetLastError( ERROR_INVALID_PARAMETER); return SF_STATUS_REQ_ERROR; } /* * Making the filter CARP-aware. We change the HTTP reply (adding the header) only * if we are the first server. Note that if this is not the first server, all the data already transferred * and there is nothing left to do. * */ BOOL IsFirst; DWORD dwErrorCode = IsFirstInCARP(pfc,&IsFirst) ; if (dwErrorCode != ERROR_SUCCESS) { SetLastError(dwErrorCode); return SF_STATUS_REQ_ERROR; } if (!IsFirst) { OutputDebugStringA("WEBRESPONSEMODIFIER: OnEndOfRequest, intra array server, do nothing./n"); return SF_STATUS_REQ_NEXT_NOTIFICATION; } OutputDebugStringA("WEBRESPONSEMODIFIER: First array server, insert header and send./n"); /* * Block the following SEND_RESPONSE and END_OF_REQUEST notifications for * this request. ( WriteClient() bellow will generate them.) * */ DisableNotifications( pfc, SF_NOTIFY_END_OF_REQUEST | SF_NOTIFY_SEND_RAW_DATA); /* * OK all data was accumulated. Now extract from Request Data * the response buffer. (which now contains the complete response). */ PHTTP_FILTER_RAW_DATA pRawData = (PHTTP_FILTER_RAW_DATA)pfc->pFilterContext; if ( NULL == pRawData) { return SF_STATUS_REQ_NEXT_NOTIFICATION; } LPBYTE lpBuffer = (LPBYTE)pRawData->pvInData; DWORD bytesToSend = pRawData->cbInData; /* * Empty Request data to make it ready for next response * in case the connection is kept alive */ pfc->pFilterContext = NULL; /* * Add here code to modify the response. It is now the complete response. * any decisions and changes that demand the complete Response in hand * should be done here. */ if (!InsertOurHTMLHeader( pfc, &lpBuffer, &bytesToSend)) { SetLastError( ERROR_NOT_ENOUGH_MEMORY ); return SF_STATUS_REQ_ERROR; } /* * Send the complete response in one chunk. */ DWORD dwReserved = 0 ; if ( pfc->WriteClient(pfc,(LPVOID)lpBuffer,&bytesToSend,dwReserved) ) { return SF_STATUS_REQ_NEXT_NOTIFICATION; } else { return SF_STATUS_REQ_ERROR; } } /* * * InsertOurHTMLHeader() * Given the full response chunk, test if the response is in HTML format (has * <HTML> in it). If so, insert an HTML header line into the response * HTML. To do that we look at the input HTML as made of 3 chunks: * Chunk1 from start till "Content-Length: ..." header ( if exist.) * Chunk2 from "/r/n" after "Content-Length:" header until last character of * "<HTML>". * Chunk3 from first character after "<HTML>" till the end of the response. * We then calculate the new Content-Length value by adding the length of the * line we will insert to the original content length, and finally allocate a new * buffer and paste into it the chunks in the following order: * Chunk1, Updateded-Content-Length-Header, Chunk2, Line-we-wish-to-insert, chunk3. * */ static bool InsertOurHTMLHeader ( PHTTP_FILTER_CONTEXT pfc, LPBYTE *ppBuffer, LPDWORD lpdwLen ) { LPSTR lpBuffer = (LPSTR)*ppBuffer; DWORD dwLen = *lpdwLen; bool bStatus = true; if (lpBuffer == NULL || dwLen > INT_MAX) { bStatus = false; goto ReturnBuffer; } if ( 0 < strnstr( lpBuffer, "<HTML>", dwLen) ) { /* * * Find first chunk. If no Content-Length header then first chunk will be * zero sized. * */ int iStartChunk1 = 0; int iEndChunk1 = strnstr( lpBuffer, CONTENT_LENGTH, dwLen); if ( 0 >= iEndChunk1 ) iEndChunk1 = 0; int iTmp = 0; if ( 0 < iEndChunk1 ) { /* * * If we are here then there is a Content-Length header, so we * find the first "/r/n" after the the Content-Length header. * */ iTmp = strnstr( lpBuffer + iEndChunk1, "/r/n" , dwLen - iEndChunk1); if ( 0 >= iTmp ) goto ReturnBuffer; } /* * * Find the second chunk. It starts on the "/r/n" after the Content-Length * Header, and ends after the first "<HTML>". * */ int iStartChunk2 = iEndChunk1 + iTmp; iTmp = strnstr( lpBuffer + iStartChunk2, "<HTML>", dwLen - iStartChunk2); if ( 0 >= iTmp ) goto ReturnBuffer; int iEndChunk2 = iStartChunk2 + iTmp + STRING_SIZE("<HTML>"); /* * * The third and last chunk starts after the first "<HTML>" and goes till * the end of the input response. * */ int iStartChunk3 = iEndChunk2; int iEndChunk3 = (int)dwLen; char szContentLen[CONTENTLEN_SIZE]; if ( 0 < iEndChunk1 ) { /* * * If there is Content-Length Header then find the Input Content Length, * and add to it the length of the inserted line. * */ DWORD dwContentLen = dwfnContentLen( lpBuffer + iEndChunk1, iStartChunk2 - iEndChunk1) + STRING_SIZE(LINE_TO_INSERT); char *p = (char *) memcpy( szContentLen, CONTENT_LENGTH, STRING_SIZE(CONTENT_LENGTH)) + STRING_SIZE(CONTENT_LENGTH); *p++ = ' '; HRESULT hr = StringCchPrintfA(p, CONTENTLEN_SIZE - STRING_SIZE(CONTENT_LENGTH) - SIZEOF_CHAR, "%u", dwContentLen); if (hr != S_OK) { OutputDebugStringF("StringCchPrintfA failed"); } } else { szContentLen[0] = 0; } /* * * Allocate a buffer for the new response. * */ iTmp = iEndChunk1 - iStartChunk1 + strlen(szContentLen) + iEndChunk2 - iStartChunk2 + STRING_SIZE(LINE_TO_INSERT) + iEndChunk3 - iStartChunk3 + 1; DWORD dwReserved = 0; LPSTR lpNewBuffer = (LPSTR)pfc->AllocMem(pfc,iTmp, dwReserved); if ( !lpNewBuffer ) { bStatus = false; goto ReturnBuffer; } #define MEMCAT(lpTarget,lpSource,SourceLen,TargetLen) / memcpy(lpTarget,lpSource,SourceLen); TargetLen += SourceLen; DWORD dwNewLen = 0; MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk1, iEndChunk1 - iStartChunk1, dwNewLen); MEMCAT( lpNewBuffer + dwNewLen, szContentLen, strlen(szContentLen), dwNewLen); MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk2, iEndChunk2 - iStartChunk2, dwNewLen); MEMCAT( lpNewBuffer + dwNewLen, LINE_TO_INSERT, strlen(LINE_TO_INSERT), dwNewLen); MEMCAT( lpNewBuffer + dwNewLen, lpBuffer + iStartChunk3, iEndChunk3 - iStartChunk3, dwNewLen); /* * We don't have to do that, but making it a string is good for debugging */ lpNewBuffer[dwNewLen] = 0; lpBuffer = lpNewBuffer; dwLen = dwNewLen; } ReturnBuffer: *ppBuffer = (LPBYTE)lpBuffer; *lpdwLen = dwLen; return bStatus; } /* * * Extract the input Content-Length value. * * Note: This function receive a pointer to a string begins with "Content-Length:". * It searches for the first occurrence of ":" and tries to parse the number followed by * the ":" character. If the parsing fails, the function return 0. * */ static ULONG dwfnContentLen(__in LPSTR ContentLenLine, int iLineLen) { if (iLineLen <= 0) { return 0; } int iColumn = strnstr(ContentLenLine,":",iLineLen) + strlen(":"); if (iColumn == 0) { return 0; } char *s = new char[iLineLen - iColumn + 1]; if (!s) return 0; StringCchCopyN(s, iLineLen - iColumn + 1, &ContentLenLine[iColumn], iLineLen - iColumn); s[iLineLen - iColumn] = 0; LPSTR stopstring; DWORD dwCL = strtoul( s, &stopstring, 10 ); if (errno == ERANGE) // overflow { delete [] s; return 0; } delete [] s; return dwCL; } /* * * Utility function to notify that a filter is not to be called * to a notification throughout the lifetime of the current Request. * */ static void DisableNotifications ( PHTTP_FILTER_CONTEXT pfc, DWORD flags ) { pfc->ServerSupportFunction( pfc, SF_REQ_DISABLE_NOTIFICATIONS, NULL, flags, 0 ); } /* * strnstr() * finds first appearance of strCharSet in string ignoring * letters case. */ static int strnstr ( const char *string, const char *strCharSet , int n) { int len = (strCharSet != NULL ) ? ((int)strlen(strCharSet )) : 0 ; if ( 0 == n || 0 == len ) { return -1; } int ret = -1; BOOLEAN found = FALSE; for (int I = 0 ; I <= n - len && !(found) ; I++) { int J = 0 ; for ( ; J < len ; J++ ) { if (toupper(string[I + J]) != toupper(strCharSet [J])) { break; // Exit For(J) } } if ( J == len) { found = TRUE; ret = I; } } return ret; } void OutputDebugStringF (const char* pchFormat, ...) { assert (pchFormat != 0); va_list vaParams; va_start (vaParams, pchFormat); char pchMessage[1024]; StringCchVPrintf (pchMessage, sizeof (pchMessage), pchFormat, vaParams); pchMessage[sizeof(pchMessage)-1] = '/0'; OutputDebugStringA (pchMessage); va_end (vaParams); } /* * IsFirstInCARP() * Returns in IsFirst variable true if the current server is the first server and false otherwise. */ static DWORD IsFirstInCARP(PHTTP_FILTER_CONTEXT pfc, BOOL *pfIsFirst) { char chBuf[2]={0}; DWORD dwBufSize = sizeof(chBuf); if (pfIsFirst == NULL || pfc == NULL) { return ERROR_INVALID_PARAMETER; } if( !pfc->GetServerVariable(pfc, "IS_INTRA_ARRAY_TRAFFIC", chBuf, &dwBufSize) ) { DWORD dwError = GetLastError(); if (dwError == ERROR_INVALID_INDEX ) { /* * We get here in case that the variable "IS_INTRA_ARRAY_TRAFFIC" is undefined. * This means that we are running on ISA SE and therefore act as if we are the first server in the array. */ OutputDebugStringA("WEBRESPONSEMODIFIER: running ISA SE - this is the first server./n"); *pfIsFirst = TRUE; return ERROR_SUCCESS; } OutputDebugStringA("WEBRESPONSEMODIFIER: GetServerVariable failed./n"); return dwError; } if (chBuf[0] == '1') { *pfIsFirst = FALSE; OutputDebugStringA("WEBRESPONSEMODIFIER: intra array traffic./n"); } else { *pfIsFirst = TRUE; OutputDebugStringA("WEBRESPONSEMODIFIER: First array server./n"); } return ERROR_SUCCESS; }