Small fix for dnsredir

dnsredir.c

@@ -50,6 +50,22 @@ typedef struct udp_connrecord {
 static time_t last_cleanup = 0;
 static udp_connrecord_t *conntrack = NULL;
 
+void flush_dns_cache() {
+    BOOL WINAPI (*DnsFlushResolverCache)();
+
+    HMODULE dnsapi = LoadLibrary("dnsapi.dll");
+    if (dnsapi == NULL)
+    {
+        printf("Can't load dnsapi.dll to flush DNS cache!\n");
+        exit(EXIT_FAILURE);
+    }
+
+    DnsFlushResolverCache = (void*)GetProcAddress(dnsapi, "DnsFlushResolverCache");
+    if (DnsFlushResolverCache == NULL || !DnsFlushResolverCache())
+        printf("Can't flush DNS cache!");
+    FreeLibrary(dnsapi);
+}
+
 inline static void construct_key(const uint32_t srcip, const uint16_t srcport, char *key) {
     debug("Construct key enter\n");
     if (key) {

dnsredir.h

@@ -15,3 +15,5 @@ int dns_handle_incoming(const uint32_t srcip, const uint16_t srcport,
 int dns_handle_outgoing(const uint32_t srcip, const uint16_t srcport,
                         const uint32_t dstip, const uint16_t dstport,
                         const char *packet_data, const UINT packet_dataLen);
+
+void flush_dns_cache();

goodbyedpi.c

@@ -22,6 +22,7 @@
 #define TCP_HDR_LEN 20
 #define IPV4_TOTALLEN_OFFSET 2
 #define TCP_WINDOWSIZE_OFFSET 14
+#define HOST_MAXLEN 253
 
 #define DIVERT_NO_LOCALNETS_DST "(" \
                    "(ip.DstAddr < 127.0.0.1 or ip.DstAddr > 127.255.255.255) and " \
@@ -64,7 +65,8 @@ static struct option long_options[] = {
     {0,           0,                 0,   0  }
 };
 
-static char *filter_string = "(ip and tcp and "
+static char *filter_string = NULL;
+static char *filter_string_template = "(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)"
@@ -251,6 +253,11 @@ int main(int argc, char *argv[]) {
     char *hdr_name_addr = NULL, *hdr_value_addr = NULL;
     int hdr_value_len;
 
+    if (filter_string == NULL) {
+        filter_string = malloc(strlen(filter_string_template) + 1);
+        strcpy(filter_string, filter_string_template);
+    }
+
     printf("GoodbyeDPI: Passive DPI blocker and Active DPI circumvention utility\n");
 
     if (argc == 1) {
@@ -319,10 +326,12 @@ int main(int argc, char *argv[]) {
                     printf("Port parameter error!\n");
                     exit(EXIT_FAILURE);
                 }
+                if (i != 80 && i != 443)
                     add_filter_str(IPPROTO_TCP, i);
                 i = 0;
                 break;
             case 'd':
+                if (!do_dns_redirect) {
                     do_dns_redirect = 1;
                     dns_addr = inet_addr(optarg);
                     if (!dns_addr) {
@@ -330,14 +339,24 @@ int main(int argc, char *argv[]) {
                         exit(EXIT_FAILURE);
                     }
                     add_filter_str(IPPROTO_UDP, 53);
+                    flush_dns_cache();
+                }
                 break;
             case 'g':
+                if (!do_dns_redirect) {
+                    printf("--dns-port should be used with --dns-addr!\n"
+                        "Make sure you use --dns-addr and pass it before "
+                        "--dns-port\n");
+                    exit(EXIT_FAILURE);
+                }
                 dns_port = atoi(optarg);
                 if (dns_port <= 0 || dns_port > 65535) {
                     printf("DNS port parameter error!\n");
                     exit(EXIT_FAILURE);
                 }
+                if (dns_port != 53) {
                     add_filter_str(IPPROTO_UDP, dns_port);
+                }
                 dns_port = ntohs(dns_port);
                 break;
             default:
@@ -445,7 +464,7 @@ int main(int argc, char *argv[]) {
                         host_addr = hdr_value_addr;
                         host_len = hdr_value_len;
 
-                        if (do_host_mixedcase && host_len > 0 && host_len <= 253) {
+                        if (do_host_mixedcase && host_len > 0 && host_len <= HOST_MAXLEN) {
                             mix_case(host_addr, host_len);
                             should_recalc_checksum = 1;
                         }
@@ -486,7 +505,7 @@ int main(int argc, char *argv[]) {
                                  *
                                  * Nothing is done if User-Agent header is missing.
                                  */
-                                if (host_len > 0 && host_len <= 253 &&
+                                if (host_len > 0 && host_len <= HOST_MAXLEN &&
                                     useragent_addr && useragent_len > 0) {
                                     /* useragent_addr is in the beginning of User-Agent value */
 
@@ -515,7 +534,7 @@ int main(int argc, char *argv[]) {
                                         should_recalc_checksum = 1;
                                         //printf("Replaced Host header!\n");
                                     }
-                                } /* if (host_len <= 253 && useragent_addr) */
+                                } /* if (host_len <= HOST_MAXLEN && useragent_addr) */
                             } /* if (find_header_and_get_info http_useragent) */
                         } /* else if (do_host_removespace) */
                     } /* if (find_header_and_get_info http_host) */
@@ -541,7 +560,7 @@ int main(int argc, char *argv[]) {
             }
 
             /* Else if we got UDP packet with data */
-            else if (WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
+            else if (do_dns_redirect && WinDivertHelperParsePacket(packet, packetLen, &ppIpHdr,
                 NULL, NULL, NULL, NULL, &ppUdpHdr, &packet_data, &packet_dataLen)) {
 
                 if (addr.Direction == WINDIVERT_DIRECTION_INBOUND) {