Do not handle traffic from private IP ranges

Some servers set "don't fragment" flag and never increase TCP ID
field. If they send HTTP redirection to another website, it would
be blocked by the program.
This is a hack to block redirects only with "Connection: close"
header as presumably legal redirects are most likely would
use keep-alive.

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

@@ -21,6 +21,21 @@
 #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;
 static const char *http10_redirect_302 = "HTTP/1.0 302 ";
@@ -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 ",
@@ -61,9 +77,15 @@ 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 +113,9 @@ 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 */
+        /* Then check if this is a redirect to new http site with Connection: close */
-        if (dumb_memmem(pktdata, pktlen, location_http, strlen(location_http))) {
+        if (dumb_memmem(pktdata, pktlen, location_http, strlen(location_http)) &&
+            dumb_memmem(pktdata, pktlen, connection_close, strlen(connection_close))) {
             return 1;
         }
     }
@@ -230,21 +253,30 @@ int main(int argc, char *argv[]) {
     filter_num = 0;
 
     if (do_passivedpi) {
-        /* Filter for inbound RST packets with ID = 0 or 1 */
+        /* IPv4 filter for inbound RST packets with ID = 0 or 1 */
-        filters[filter_num] = init("inbound and (ip.Id == 0x0001 or ip.Id == 0x0000) and "
+        filters[filter_num] = init(
-                        "(tcp.SrcPort == 443 or tcp.SrcPort == 80) and tcp.Rst",
+            "inbound and ip and tcp and "
-                        WINDIVERT_FLAG_DROP);
+            "(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) "
+    filters[filter_num] = init("ip and tcp and "
-                      "or (inbound and (tcp.SrcPort == 80 or tcp.SrcPort == 443) and tcp.Ack and tcp.Syn) "
+        "(inbound and (("
-                      "or (outbound and (tcp.DstPort == 80 or tcp.DstPort == 443) and tcp.Ack)",
+         "((ip.Id == 0x0001 or ip.Id == 0x0000) and tcp.SrcPort == 80 and tcp.Ack) or "
-                      0);
+         "((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++;