Added SCTP handling for masquerading

This was easier than expected... since masquerading changes an address,
but not the SCTP common header and further SCTP details, it does not
[seem to] pass into the SCTP checksum, as that uses no pseudo IP header AFAIK.
So, the [complicating] CRC-32 checksum computation need not be redone :-)
There is a need to update UDP signatures, also for an SCTP tunnel, and when
SCTP is the IPv6 payload there should be no checksum updated anywhere.
[We currently have too much code as a result of that, for sctp_offset.]

diff --git a/6bed4router.c b/6bed4router.c
index 7ca26e2..63b099d 100644 (file)
--- a/6bed4router.c
+++ b/6bed4router.c
@@ -25,6 +25,7 @@
  */
 
 
+#include <stddef.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -110,13 +111,17 @@ struct {
                        struct ip6_hdr v6hdr;
                        uint8_t data [MTU - sizeof (struct ip6_hdr)];
                } idata;
-               struct {
+               struct v4frame {
                        struct ip6_hdr v6hdr;
                        union {
                                struct icmp6_hdr  v6icmphdr;
                                struct my_sctphdr v6sctphdr;
                                struct tcphdr     v6tcphdr ;
                                struct udphdr     v6udphdr ;
+                               struct {
+                                       struct udphdr     v6udphdr;
+                                       struct my_sctphdr v6sctphdr;
+                               } tdata;
                        } adata;
                } ndata;
        } udata;
@@ -138,10 +143,16 @@ struct {
 #define v4v6icmpcode   ( v4data6.udata.ndata.adata.v6icmphdr.icmp6_code)
 #define v4v6icmpcksum  ( v4data6.udata.ndata.adata.v6icmphdr.icmp6_cksum)
 
+#define v4v6sctpofs    (offsetof (struct v4frame,adata.v6sctphdr))
 #define v4v6sctpsrcport        ( v4data6.udata.ndata.adata.v6sctphdr.source)
 #define v4v6sctpdstport        ( v4data6.udata.ndata.adata.v6sctphdr.dest)
 #define v4v6sctpcksum  ( v4data6.udata.ndata.adata.v6sctphdr.cksum)
 
+#define v4v6tunsctpofs (offsetof (struct v4frame,adata.tdata.v6sctphdr))
+#define v4v6tunsctpsrcport ( v4data6.udata.ndata.adata.tdata.v6sctphdr.source)
+#define v4v6tunsctpdstport ( v4data6.udata.ndata.adata.tdata.v6sctphdr.dest)
+#define v4v6tunsctpcksum   ( v4data6.udata.ndata.adata.tdata.v6sctphdr.cksum)
+
 #define v4v6tcpsrcport ( v4data6.udata.ndata.adata.v6tcphdr.source)
 #define v4v6tcpdstport ( v4data6.udata.ndata.adata.v6tcphdr.dest)
 #define v4v6tcpcksum   ( v4data6.udata.ndata.adata.v6tcphdr.check)
@@ -157,13 +168,17 @@ struct {
        struct tun_pi tun;
        union {
                uint8_t data [MTU];
-               struct {
+               struct v6frame {
                        struct ip6_hdr v6hdr;
                        union {
                                struct icmp6_hdr  v6icmphdr;
                                struct my_sctphdr v6sctphdr;
                                struct tcphdr     v6tcphdr ;
                                struct udphdr     v6udphdr ;
+                               struct {
+                                       struct udphdr     v6udphdr;
+                                       struct my_sctphdr v6sctphdr;
+                               } tdata;
                        } adata;
                } ndata;
        } udata;
@@ -182,10 +197,16 @@ struct {
 #define v6icmpcksum    ( v6data6.udata.ndata.adata.v6icmphdr.icmp6_cksum)
 
 #define v6sctpcksum    ( v6data6.udata.ndata.adata.v6sctphdr.cksum)
+#define v6tunsctpcksum ( v6data6.udata.ndata.adata.tdata.v6sctphdr.cksum)
+
+#define v6sctpofs      (offsetof(struct v6frame,adata.v6sctphdr))
+#define v6tunsctpofs   (offsetof(struct v6frame,adata.tdata.v6sctphdr))
 
 #define v6tcpcksum     ( v6data6.udata.ndata.adata.v6tcphdr.check)
 
 #define v6udpcksum     ( v6data6.udata.ndata.adata.v6udphdr.check)
+#define v6udpdstport   ( v6data6.udata.ndata.adata.v6udphdr.dest)
+#define v6udpsrcport   ( v6data6.udata.ndata.adata.v6udphdr.source)
 
 
 uint8_t router_linklocal_address [] = {
@@ -520,18 +541,6 @@ bool validate_originator (struct in6_addr *ip6) {
 
 
 /*
- * Given a protocol and a port number, locate the masqhost that would match.
- * The protocol is 0 for SCTP, 1 for TCP, 2 for UDP (alphabetic sequence).
- * Returns a pointer to the address or NULL if not found.
- */
-uint8_t *protoport2masqhost (uint8_t proto, uint16_t port) {
-       //NOTUSED// TODO:IMPLEMENT
-       return NULL;
-}
-
-
-
-/*
  * Major packet processing functions
  */
 
@@ -658,15 +667,16 @@ void handle_4to6_masquerading (ssize_t v4datalen) {
        uint16_t numpairs = 0;
        uint16_t port = 0;
        uint16_t *csum_field = NULL;
+       uint16_t sctp_offset = 0;
+       uint16_t skip_csum;
        switch (v4v6nexthdr) {
-#ifdef CHECKSUM_SCTP_WOULD_BE_LIKE_FOR_OTHERS
        case IPPROTO_SCTP:
                portpairs = masqportpairs [0];  // 's'
                numpairs  = num_masqportpairs [0];
                port = ntohs (v4v6sctpdstport);
-               csum_field = &v4v6sctpcksum;
+               csum_field = &skip_csum;
+               sctp_offset = v4v6sctpofs;
                break;
-#endif
        case IPPROTO_TCP:
                portpairs = masqportpairs [1];  // 't'
                numpairs  = num_masqportpairs [1];
@@ -678,6 +688,13 @@ void handle_4to6_masquerading (ssize_t v4datalen) {
                numpairs  = num_masqportpairs [2];
                port = ntohs (v4v6udpdstport);
                csum_field = &v4v6udpcksum;
+               if ((port == 9899) && (v4v6udpsrcport == v4v6udpdstport)) {
+                       // SCTP tunneled over UDP (keep csum_field)
+                       portpairs = masqportpairs [0];
+                       numpairs = num_masqportpairs [0];
+                       port = ntohs (v4v6tunsctpdstport);
+                       sctp_offset = v4v6tunsctpofs;
+               }
                break;
        case IPPROTO_ICMPV6:
                portpairs = icmp_portpairs;
@@ -697,6 +714,12 @@ void handle_4to6_masquerading (ssize_t v4datalen) {
                        masquerade_address (v4dst6,
                                (struct in6_addr *) masqhost [portpairs [2]],
                                csum_field);
+                       if (sctp_offset > 0) {
+                               //TODO// Recompute SCTP's CRC-32 checksum
+                               // recompute_sctp_checksum (ip6hdr, sctp_offset, framelen);
+                               //BUT: SCTP checksum does not use pseudo IPhdr
+                               //SO:  Address masquerading goes undetected :-D
+                       }
                        //
                        // Forward immediately, and return from this function
 printf ("Writing Masqueraded IPv6, result = %zd\n",
@@ -853,18 +876,24 @@ printf ("Received plain unicast IPv6 data, flags=0x%04x, proto=0x%04x\n", v6tunc
                if (memcmp (v6src6, masqhost [mqh], 16) == 0) {
 printf ("Masqueraded sender address in 6to4 set to the client's 6bed4router address\n");
                        uint16_t *csum_field = NULL;
+                       uint16_t fake_csum;
                        struct in6_addr masq_src;
+                       uint16_t sctp_offset = 0;
                        switch (v6nexthdr) {
-#ifdef CHECKSUM_SCTP_WOULD_BE_LIKE_FOR_OTHERS
                        case IPPROTO_SCTP:
-                               csum_field = &v6sctpcksum;
+                               csum_field = &fake_csum;
+                               sctp_offset = v6sctpofs;
                                break;
-#endif
                        case IPPROTO_TCP:
                                csum_field = &v6tcpcksum;
                                break;
                        case IPPROTO_UDP:
                                csum_field = &v6udpcksum;
+                               if ((v6udpsrcport == v6udpdstport) &&
+                                               (v6udpsrcport == htons (9899))) {
+                                       // SCTP tunneled over UDP
+                                       sctp_offset = v6tunsctpofs;
+                               }
                                break;
                        case IPPROTO_ICMPV6:
                                csum_field = &v6icmpcksum;
@@ -878,6 +907,12 @@ printf ("Masqueraded sender address in 6to4 set to the client's 6bed4router addr
                        masq_src.s6_addr16 [7] &= htons (0xc000);
                        fprintf (stderr, "Masquerading cksum.old = 0x%04x, ", ntohs (*csum_field));
                        masquerade_address (v6src6, &masq_src, csum_field);
+                       if (sctp_offset > 0) {
+                               //TODO// Recompute SCTP's CRC-32 checksum
+                               // recompute_sctp_checksum (ip6hdr, sctp_offset, framelen);
+                               //BUT: SCTP checksum does not use pseudo IPhdr
+                               //SO:  Address masquerading goes undetected :-D
+                       }
                        fprintf (stderr, "cksum.new = 0x%04x\n", ntohs (*csum_field));
                        break;
                }