Osmocom Libraries » libosmo-sccp + libosmo-sigtran

Started work on this. WIP can be found at:
libosmo-netif.git branch "pespin/primary"
libosmo-sccp.git branch "pespin/primary"

I submitted a bunch of patches to libosmo-netif fixing and improving several issues around existing osmo_stream code.

On top I have a patch which right now applying the Primary addresses configured in libosmo-sccp's VTY (osmo-bsc) using setsockopt (I still need to decide whether that code will belong to osmo_stream or will be handled by the osmo_stream user):

cs7 instance 0
 point-code 0.0.2
 asp asp0 2905 0 m3ua
  local-ip 127.0.0.2
  local-ip 127.123.0.2 primary
  local-ip ::1
  remote-ip 127.0.0.1
  remote-ip 127.123.0.1 primary
  remote-ip ::1
  role asp
  sctp-role client

ASP name now prints the configured primary address (marked with a "*"):

20230804203810956 DLSS7 osmo_ss7.c:1696 0: asp-asp0: Restarting ASP asp0, r=(127.0.0.1|127.123.0.1*|::1):2905<->l=(127.0.0.2|127.123.0.2*|::1):0

the setsockopt() are still failing for some reason I need to find out:

20230804203810957 DLINP stream_cli.c:353 CLICONN(asp0,r=::1:2905<->l=::ffff:127.0.0.2:40825){CONNECTING} connection established
20230804203810957 DLINP stream.c:106 sizes of 'struct sctp_event_subscribe': compile-time 14, kernel: 14
20230804203810957 DLINP stream_cli.c:368 CLICONN(asp0,r=::1:2905<->l=::ffff:127.0.0.2:40825){CONNECTED} Set Peer's Primary Address 127.123.0.2
20230804203810957 DLINP stream.c:228 setsockopt(SCTP_SET_PEER_PRIMARY_ADDR, 127.123.0.2) failed: Operation not permitted
20230804203810957 DLINP stream_cli.c:373 CLICONN(asp0,r=::1:2905<->l=::ffff:127.0.0.2:40825){CONNECTED} Set Primary Address 127.123.0.1
20230804203810957 DLINP stream.c:250 setsockopt(SCTP_PRIMARY_ADDR, 127.123.0.1) failed: Invalid argument

Related code is here:

+int stream_setsockopt_peer_primary_addr(int fd, const struct osmo_sockaddr *saddr)
+{
+       int rc;
+
+       struct sctp_setpeerprim so_sctp_setpeerprim = {0};
+
+       /* rfc6458 sec 8: "For the one-to-one style sockets and branched-off one-to-many
+        * style sockets (see Section 9.2), this association ID parameter is ignored" 
+        */
+
+       so_sctp_setpeerprim.sspp_addr = saddr->u.sas;
+       rc = setsockopt(fd, IPPROTO_SCTP, SCTP_SET_PEER_PRIMARY_ADDR,
+                       &so_sctp_setpeerprim, sizeof(so_sctp_setpeerprim));
+       if (rc < 0) {
+               char buf[128];
+               strerror_r(errno, (char *)buf, sizeof(buf));
+               LOGP(DLINP, LOGL_ERROR, "setsockopt(SCTP_SET_PEER_PRIMARY_ADDR, %s) failed: %s\n",
+                    osmo_sockaddr_to_str(saddr), buf);
+       }
+       return rc;
+}
+
+int stream_setsockopt_primary_addr(int fd, const struct osmo_sockaddr *saddr)
+{
+       int rc;
+
+       struct sctp_prim so_sctp_prim = {0};
+
+       /* rfc6458 sec 8: "For the one-to-one style sockets and branched-off one-to-many
+        * style sockets (see Section 9.2), this association ID parameter is ignored" 
+        */
+
+       so_sctp_prim.ssp_addr = saddr->u.sas;
+       rc = setsockopt(fd, IPPROTO_SCTP, SCTP_PRIMARY_ADDR,
+                       &so_sctp_prim, sizeof(so_sctp_prim));
+       if (rc < 0) {
+               char buf[128];
+               strerror_r(errno, (char *)buf, sizeof(buf));
+               LOGP(DLINP, LOGL_ERROR, "setsockopt(SCTP_PRIMARY_ADDR, %s) failed: %s\n",
+                    osmo_sockaddr_to_str(saddr), buf);
+       }
+       return rc;
+}

The "Operation not permitted" during "setsockopt(SCTP_SET_PEER_PRIMARY_ADDR)" failed due to sysctl "net.sctp.addip_enable" being set to 0 (the default, meaning ASCONF is disabled by default). Setting it to "1" allows applying the setsockopt and one can see ASCONF being sent to the peer at that time.

I also had to enable sysctl "net.sctp.auth_enable=1" together with net.sctp.addip_enable, otherwise the stack sends INIT with SupportedExtensions=ASCONF,ASCONF_ACK, but the spec says that in order to support the feature it MUST also have "AUTH" extension in the list. If that's not added, the server side answers with an ABORT (unless sysctl net.sctp.addip_noauth_enable is set to 1 afaik).

All this is specified in RFC 5061 section 4.2.7 "Supported Extensions Parameter", and also mentioned in the linux kernel at sctp_make_init():
https://github.com/torvalds/linux/blob/master/net/sctp/sm_make_chunk.c#L254

I attach a pcap showing the feature in action (configured through the "primary" keyword in the VTY configs shared previously in this ticket).

One can see that the primary addresses are not used starting from the instant moment when they are requested, but only after they have been confirmed through HEARTBEAT ping-pong. One can see both sides initially using the first address in the VTY list (implementation detail, if first would fail during INIT, the second would be taken, and so on), Then, after applying primary address and also applying peer's primary addr (ASCONF), after HEARTBEATs occur, then both start using those primary addresses (127.123.0.{1,2}).

I have implemented the initial applying of (Peer) Primary Address here:
https://gerrit.osmocom.org/c/libosmo-sccp/+/34111 asp: Allow setting IP address as SCTP primary upon conn establishment

Also, another patch which monitors state of the addresses and re-applies Primary Address once it is available again, or if the peer attempts to change it through ASCONF:
https://gerrit.osmocom.org/c/libosmo-sccp/+/34112 asp: Monitor SCTP_PEER_ADDR_CHANGE events to re-apply configured Primary Address

I attach a new pcap showing the behavior, using similar configs as shared above in this ticket (now with the primary address being 192.168.123.{1,2}). What I do in this test is have those 192.168.123.{1,2} addresses assign to some given interface in my system, and after a while, I remove 192.168.123.1 from the interface. Eventually, the client (who whas the primary set to it) find out and logs about it. Then I re-add the IP address and it can be seen how the client finds about it becoming available again and hence re-applies it as Primary Address.

I am now enabling ACONF (dependend AUTH) feature per-socket using this patch:
https://gerrit.osmocom.org/c/libosmocore//34113 socket: Add osmo_sock_init flag to enable SCTP ASCONF features
https://gerrit.osmocom.org/c/libosmo-netif/+/34114 stream: Use new flag OSMO_SOCK_F_SCTP_ASCONF_SUPPORTED for SCTP sockets

All patches implementing the feature have been merged.

Only missing part: Document the new "primary" parameter in user manual, and provide a small description on what's it's meaning for local and remote IP addresses.

Documentation available in OsmoBSC/MSC/STP User Manual, eg https://ftp.osmocom.org/docs/osmo-bsc/master/osmobsc-usermanual.pdf section "8.5.6 SCTP Primary Address"