Update Makefile

We can't reliably distinguish HTTP data from other data on port 80 when fragmentation is used.
HTTP method code has a special case which tries to find HTTP method when fragmentation = 1 or 2 is used,
but not for other values.

Makefile

@@ -7,7 +7,8 @@ LIBS = -L $(WINDIVERTLIBS) -lWinDivert -lws2_32
 CC = $(CPREFIX)-gcc
 CCWINDRES = $(CPREFIX)-windres
 CFLAGS = -Wall -I $(WINDIVERTHEADERS) -L $(WINDIVERTLIBS) \
-         -O2 -fPIE -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2
+         -O2 -pie -fPIE -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2
+LDFLAGS = -pie
 
 .PHONY: default all clean
 

README.md

@@ -38,7 +38,7 @@ Use `goodbyedpi.exe -4` if it works for your ISP's DPI. This is the fastest mode
 
 ### Passive DPI
 
-Most Passive DPI send HTTP 302 Redirect if you try to access blocked website over HTTP and TCP Reset in case of HTTPS, faster than destination website. Packets sent by DPI have always have IP Identification field equal to `0x0000` or `0x0001`, as seen with Russian providers. These packets, if they redirect you to another website (censorship page), are blocked by GoodbyeDPI.
+Most Passive DPI send HTTP 302 Redirect if you try to access blocked website over HTTP and TCP Reset in case of HTTPS, faster than destination website. Packets sent by DPI always have IP Identification field equal to `0x0000` or `0x0001`, as seen with Russian providers. These packets, if they redirect you to another website (censorship page), are blocked by GoodbyeDPI.
 
 ### Active DPI
 
@@ -49,7 +49,7 @@ Active DPI is more tricky to fool. Currently the software uses 4 methods to circ
 * Removing space between header name and value in `Host` header
 * Adding additional space between HTTP Method (GET, POST etc) and URI
 
-These methods should not break any website as are fully compatible with TCP and HTTP standards, yet it's sufficient to prevent DPI data classification and to circumvent censorship. Additional space may break some websites, although it's acceptable by HTTP/1.1 specification (see 19.3 Tolerant Applications).
+These methods should not break any website as they're fully compatible with TCP and HTTP standards, yet it's sufficient to prevent DPI data classification and to circumvent censorship. Additional space may break some websites, although it's acceptable by HTTP/1.1 specification (see 19.3 Tolerant Applications).
 
 The program loads WinDivert driver which uses Windows Filtering Platform to set filters and redirect packets to the userspace. It's running as long as console window is visible and terminates when you close the window.
 
@@ -68,7 +68,7 @@ And for x86_64:
 # How to install as Windows Service
 
 One way is using an [srvstart](http://www.rozanski.org.uk/software) program.  
-Unpack it to goodbyedpi directory and create 3 files:
+Unpack it to `goodbyedpi` directory and create 3 files:
 
 *goodbyedpi.ini*
 ```INI
@@ -79,7 +79,7 @@ auto_restart=n
 ```
 *srvinstall.bat*
 ```Batchfile
-srvstart install GoodByeDPI -c %CD%\goodbyedpi-svc.ini
+srvstart install GoodByeDPI -c %CD%\goodbyedpi.ini
 ```
 *srvremove.bat*
 ```Batchfile

goodbyedpi.c

@@ -20,6 +20,21 @@
 #define TCP_HDR_LEN 20
 #define IPV4_TOTALLEN_OFFSET 2
 #define TCP_WINDOWSIZE_OFFSET 14
+
+#define DIVERT_NO_LOCALNETS_DST "(" \
+                   "(ip.DstAddr < 127.0.0.1 or ip.DstAddr > 127.255.255.255) and " \
+                   "(ip.DstAddr < 10.0.0.0 or ip.DstAddr > 10.255.255.255) and " \
+                   "(ip.DstAddr < 192.168.0.0 or ip.DstAddr > 192.168.255.255) and " \
+                   "(ip.DstAddr < 172.16.0.0 or ip.DstAddr > 172.31.255.255) and " \
+                   "(ip.DstAddr < 169.254.0.0 or ip.DstAddr > 169.254.255.255)" \
+                   ")"
+#define DIVERT_NO_LOCALNETS_SRC "(" \
+                   "(ip.SrcAddr < 127.0.0.1 or ip.SrcAddr > 127.255.255.255) and " \
+                   "(ip.SrcAddr < 10.0.0.0 or ip.SrcAddr > 10.255.255.255) and " \
+                   "(ip.SrcAddr < 192.168.0.0 or ip.SrcAddr > 192.168.255.255) and " \
+                   "(ip.SrcAddr < 172.16.0.0 or ip.SrcAddr > 172.31.255.255) and " \
+                   "(ip.SrcAddr < 169.254.0.0 or ip.SrcAddr > 169.254.255.255)" \
+                   ")"
     
 static HANDLE filters[MAX_FILTERS];
 static int filter_num = 0;
@@ -29,6 +44,7 @@ static const char *http_host_find = "\r\nHost: ";
 static const char *http_host_replace = "\r\nhoSt: ";
 static const char *http_useragent_find = "\r\nUser-Agent: ";
 static const char *location_http = "\r\nLocation: http://";
+static const char *connection_close = "\r\nConnection: close";
 static const char *http_methods[] = {
     "GET ",
     "HEAD ",
@@ -37,15 +53,6 @@ static const char *http_methods[] = {
     "DELETE ",
     "CONNECT ",
     "OPTIONS ",
-    "TRACE ",
-    "PATCH ",
-    "PROPFIND ",
-    "PROPPATCH ",
-    "MKCOL ",
-    "COPY ",
-    "MOVE ",
-    "LOCK ",
-    "UNLOCK ",
 };
 
 static char* dumb_memmem(const char* haystack, int hlen, const char* needle, int nlen) {
@@ -61,9 +68,15 @@ static char* dumb_memmem(const char* haystack, int hlen, const char* needle, int
 }
 
 static HANDLE init(char *filter, UINT64 flags) {
+    LPTSTR errormessage = NULL;
     filter = WinDivertOpen(filter, WINDIVERT_LAYER_NETWORK, 0, flags);
     if (filter != INVALID_HANDLE_VALUE)
         return filter;
+    FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+                  FORMAT_MESSAGE_IGNORE_INSERTS,
+                  NULL, GetLastError(), MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
+                  (LPTSTR)&errormessage, 0, NULL);
+    printf("%s", errormessage);
     return NULL;
 }
 
@@ -91,8 +104,9 @@ static int is_passivedpi_redirect(const char *pktdata, int pktlen) {
     if (memcmp(pktdata, http11_redirect_302, strlen(http11_redirect_302)) == 0 ||
         memcmp(pktdata, http10_redirect_302, strlen(http10_redirect_302)) == 0)
     {
-        /* Then check if this is a redirect to new http site */
-        if (dumb_memmem(pktdata, pktlen, location_http, strlen(location_http))) {
+        /* Then check if this is a redirect to new http site with Connection: close */
+        if (dumb_memmem(pktdata, pktlen, location_http, strlen(location_http)) &&
+            dumb_memmem(pktdata, pktlen, connection_close, strlen(connection_close))) {
             return 1;
         }
     }
@@ -116,11 +130,19 @@ static void change_window_size(const char *pkt, int size) {
 }
 
 /* HTTP method end without trailing space */
-static PVOID find_http_method_end(const char *pkt) {
+static PVOID find_http_method_end(const char *pkt, int offset) {
     int i;
     for (i = 0; i<(sizeof(http_methods) / sizeof(*http_methods)); i++) {
         if (memcmp(pkt, http_methods[i], strlen(http_methods[i])) == 0) {
-            return (char*)pkt+strlen(http_methods[i]) - 1;
+            return (char*)pkt + strlen(http_methods[i]) - 1;
+        }
+        /* Try to find HTTP method in a second part of fragmented packet */
+        if ((offset == 1 || offset == 2) &&
+            memcmp(pkt, http_methods[i] + offset,
+                   strlen(http_methods[i]) - offset) == 0
+           )
+        {
+            return (char*)pkt + strlen(http_methods[i]) - offset - 1;
         }
     }
     return NULL;
@@ -129,7 +151,7 @@ static PVOID find_http_method_end(const char *pkt) {
 int main(int argc, char *argv[]) {
     static const char fragment_size_message[] =
                 "Fragment size should be in range [0 - 65535]\n";
-    int i, should_reinject = 0;
+    int i, should_reinject, should_recalc_checksum = 0;
     int opt;
     HANDLE w_filter = NULL;
     WINDIVERT_ADDRESS addr;
@@ -226,25 +248,40 @@ int main(int argc, char *argv[]) {
            (do_fragment_https ? https_fragment_size : 0),
            do_host, do_host_removespace, do_additional_space);
 
+    if (do_fragment_http && http_fragment_size > 2) {
+        printf("WARNING: HTTP fragmentation values > 2 are not fully compatible "
+               "with other options. Please use values <= 2 or disable HTTP fragmentation "
+               "completely.\n");
+    }
+
     printf("\nOpening filter\n");
     filter_num = 0;
 
     if (do_passivedpi) {
-        /* Filter for inbound RST packets with ID = 0 or 1 */
-        filters[filter_num] = init("inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and "
-                        "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst",
-                        WINDIVERT_FLAG_DROP);
+        /* IPv4 filter for inbound RST packets with ID = 0 or 1 */
+        filters[filter_num] = init(
+            "inbound and ip and tcp and "
+            "(ip.Id == 0x0001 or ip.Id == 0x0000) and "
+            "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst and "
+            DIVERT_NO_LOCALNETS_SRC,
+            WINDIVERT_FLAG_DROP);
         filter_num++;
     }
 
     /* 
-     * Filter for inbound HTTP redirection packets and
+     * IPv4 filter for inbound HTTP redirection packets and
      * active DPI circumvention
      */
-    filters[filter_num] = init("(inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and tcp.SrcPort == 80 and tcp.Ack) "
-                      "or (inbound and (tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn) "
-                      "or (outbound and (tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack)",
-                      0);
+    filters[filter_num] = init("ip and tcp and "
+        "(inbound and (("
+         "((ip.Id == 0x0001 or ip.Id == 0x0000) and tcp.SrcPort == 80 and tcp.Ack) or "
+         "((tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn)"
+         ") and " DIVERT_NO_LOCALNETS_SRC ") or "
+        "(outbound and "
+         "(tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack and "
+         DIVERT_NO_LOCALNETS_DST ")"
+        ")",
+        0);
 
     w_filter = filters[filter_num];
     filter_num++;
@@ -262,6 +299,7 @@ int main(int argc, char *argv[]) {
             //printf("Got %s packet, len=%d!\n", addr.Direction ? "inbound" : "outbound",
             //       packetLen);
             should_reinject = 1;
+            should_recalc_checksum = 0;
 
             if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                 NULL, NULL, NULL, &ppTcpHdr, NULL, &packet_data, &packet_dataLen)) {
@@ -281,8 +319,10 @@ int main(int argc, char *argv[]) {
                 /* Handle OUTBOUND packet, search for Host header */
                 else if (addr.Direction == WINDIVERT_DIRECTION_OUTBOUND && 
                         packet_dataLen > 16 && ppTcpHdr->DstPort == htons(80) &&
-                        find_http_method_end(packet_data) &&
-                        (do_host || do_host_removespace)) {
+                        find_http_method_end(packet_data,
+                                             (do_fragment_http ? http_fragment_size : 0)) &&
+                        (do_host || do_host_removespace))
+                {
 
                     data_addr = find_host_header(packet_data, packet_dataLen);
                     if (data_addr) {
@@ -290,16 +330,19 @@ int main(int argc, char *argv[]) {
                         if (do_host) {
                             /* Replace "Host: " with "hoSt: " */
                             memcpy(data_addr, http_host_replace, strlen(http_host_replace));
+                            should_recalc_checksum = 1;
                             //printf("Replaced Host header!\n");
                         }
 
                         if (do_additional_space && do_host_removespace) {
                             /* End of "Host:" without trailing space */
                             host_addr = data_addr + strlen(http_host_find) - 1;
-                            method_addr = find_http_method_end(packet_data);
+                            method_addr = find_http_method_end(packet_data,
+                                                            (do_fragment_http ? http_fragment_size : 0));
 
                             if (method_addr) {
                                 memmove(method_addr + 1, method_addr, (PVOID)host_addr - (PVOID)method_addr);
+                                should_recalc_checksum = 1;
                             }
                         }
                         else if (do_host_removespace) {
@@ -318,36 +361,50 @@ int main(int argc, char *argv[]) {
                                  */
                                 host_len = data_addr_rn - host_addr;
                                 useragent_addr = find_useragent_header(packet_data, packet_dataLen);
-                                if (host_len <= 253 && useragent_addr && useragent_addr > host_addr) {
-                                    /* Performing action only if User-Agent header goes after Host */
-
+                                if (host_len <= 253 && useragent_addr) {
                                     useragent_addr += strlen(http_useragent_find);
                                     /* useragent_addr is in the beginning of User-Agent value */
 
                                     data_len = packet_dataLen - ((PVOID)useragent_addr - packet_data);
                                     data_addr_rn = dumb_memmem(useragent_addr,
-                                                               data_len, "\r\n", 2);
+                                                            data_len, "\r\n", 2);
                                     /* data_addr_rn is in the end of User-Agent value */
 
                                     if (data_addr_rn) {
-                                        data_len = (PVOID)data_addr_rn - (PVOID)host_addr;
+                                        if (useragent_addr > host_addr) {
+                                            /* User-Agent goes AFTER Host header */
+                                            data_len = (PVOID)data_addr_rn - (PVOID)host_addr;
 
-                                        /* Move one byte to the left from "Host:"
-                                         * to the end of User-Agen
-                                         */
-                                        memmove(host_addr - 1, host_addr, data_len);
-                                        /* Put space in the end of User-Agent header */
-                                        *(char*)(data_addr_rn - 1) = ' ';
-                                        //printf("Replaced Host header!\n");
-                                    }
-                                }
-                            }
-                        }
+                                            /* Move one byte to the LEFT from "Host:"
+                                            * to the end of User-Agent
+                                            */
+                                            memmove(host_addr - 1, host_addr, data_len);
+                                            /* Put space in the end of User-Agent header */
+                                            *(char*)(data_addr_rn - 1) = ' ';
+                                            should_recalc_checksum = 1;
+                                            //printf("Replaced Host header!\n");
+                                        }
+                                        else {
+                                            /* User-Agent goes BEFORE Host header */
+                                            data_len = (PVOID)host_addr - (PVOID)data_addr_rn - 1;
+
+                                            /* Move one byte to the RIGHT from the end of User-Agent
+                                            * to the "Host:"
+                                            */
+                                            memmove(data_addr_rn + 1, data_addr_rn, data_len);
+                                            /* Put space in the end of User-Agent header */
+                                            *(char*)(data_addr_rn) = ' ';
+                                            should_recalc_checksum = 1;
+                                            //printf("Replaced Host header!\n");
+                                        }
+                                    } /* if (dara_addr_rn) */
+                                } /* if (host_len <= 253 && useragent_addr) */
+                            } /* if (data_addr_rn) */
+                        } /* else if (do_host_removespace) */
+                    } /* if (data_addr) */
+                } /* Handle OUTBOUND packet with data */
+            } /* Handle packet with data */
 
-                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
-                    }
-                }
-            }
             /* Else if we got TCP packet without data */
             else if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                 NULL, NULL, NULL, &ppTcpHdr, NULL, NULL, NULL)) {
@@ -357,17 +414,24 @@ int main(int argc, char *argv[]) {
                     //printf("Changing Window Size!\n");
                     if (do_fragment_http && ppTcpHdr->SrcPort == htons(80)) {
                         change_window_size(packet, http_fragment_size);
-                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                        should_recalc_checksum = 1;
                     }
                     else if (do_fragment_https && ppTcpHdr->SrcPort != htons(80)) {
                         change_window_size(packet, https_fragment_size);
-                        WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                        should_recalc_checksum = 1;
                     }
                 }
             }
 
             if (should_reinject) {
                 //printf("Re-injecting!\n");
+                if (should_recalc_checksum) {
+                    WinDivertHelperCalcChecksums(packet, packetLen, 0);
+                }
+                else {
+                    WinDivertHelperCalcChecksums(packet, packetLen,
+                                                 WINDIVERT_HELPER_NO_REPLACE);
+                }
                 WinDivertSend(w_filter, packet, packetLen, &addr, NULL);
             }
         }