New subject: [OpenSER-Users] recover from previous strict routing triggered incorrectly in ALG scenario

16 Apr 2008

Hi,
Im'm cross-posting this from OpenSER-Devel because I am not 100% sure 
this is a bug.

I am trying to create openser configuration for proxy that connects 
private (VPN) network with public network. I started with a config 
similar to http://voipembedded.com/resources/openser_cr.cfg, added a 
call to force_send_socket() to send from public IP and 
rtpproxy/nathelper in bridge mode. As per config loose_route() is called 
from openser.cfg to route a sequential request within a dialog through 
record-routing.
Now when a BYE from callee comes in, it contains two Route headers: 
Route: <a.b.c.d;r2=on;lr;ftag=...> where a.b.c.d is server's public IP, 
Route: <10.0.0.100;r2=on;lr;ftag=...> where 10.0.0.100 is a private IP 
and username(a)a.b.c.d in Request-URI.

Take a look at loose_route():

/*
  * Do loose routing as defined in RFC3261
  */
int loose_route(struct sip_msg* _m, char* _s1, char* _s2)
{
     int ret;

     if (find_first_route(_m) != 0) {
         LM_DBG("There is no Route HF\n");
         return -1;
     }

     if (parse_sip_msg_uri(_m)<0) {
         LM_ERR("failed to parse Request URI\n");
         return -1;
     }

     ret = is_preloaded(_m);
     if (ret < 0) {
         return -1;
     } else if (ret == 1) {
         return after_loose(_m, 1);
     } else {
#ifdef ENABLE_USER_CHECK
         if (is_myself(&_m->parsed_uri.user, &_m->parsed_uri.host,
         _m->parsed_uri.port_no)) {
#else
         if (is_myself(&_m->parsed_uri.host, _m->parsed_uri.port_no)) {
#endif
             return after_strict(_m);
         } else {
             return after_loose(_m, 0);
         }
     }
}

Obviously, is_myself() check passes and after_strict() is called.

when after_strict() is called, it looks if the URI given in Route 
contains lr parameter which marks loose routers, if so this block of 
code is executed:
     {
         LM_DBG("Next hop: '%.*s' is loose router\n",
             uri.len, ZSW(uri.s));

         if(get_maddr_uri(&uri, &puri)!=0) {
             LM_ERR("failed to check maddr\n");
             return RR_ERROR;
         }
         if (set_dst_uri(_m, &uri) < 0) {
             LM_ERR("failed to set dst_uri\n");
             return RR_ERROR;
         }

         /* Next hop is a loose router - Which means that is is not 
endpoint yet
          * In This case we have to recover from previous strict 
routing, that
          * means we have to find the last Route URI and put in in R-URI and
          * remove the last Route URI. */
         if (rt != hdr->parsed) {
             /* There is a previous route uri which was 2nd uri of mine
              * and must be removed here */
             rem_off = hdr->body.s;
             rem_len = rt->nameaddr.name.s - hdr->body.s;
             if (!del_lump(_m, rem_off - _m->buf, rem_len, 0)) {
                 LM_ERR("failed to remove Route HF\n");
                 return RR_ERROR;
             }
         }

         res = find_rem_target(_m, &hdr, &rt, &prev);
         if (res < 0) {
             LM_ERR("searching for last Route URI failed\n");
             return RR_ERROR;
         } else if (res > 0) {
             /* No remote target is an error */
             return RR_ERROR;
         }

         uri = rt->nameaddr.uri;
         if(get_maddr_uri(&uri, 0)!=0) {
             LM_ERR("checking maddr failed\n");
             return RR_ERROR;
         }
         if (rewrite_uri(_m, &uri) < 0) {
             LM_ERR("failed to rewrite R-URI\n");
             return RR_ERROR;
         }

         /* The first character if uri will be either '<' when it is the
          * only URI in a Route header field or ',' if there is more than
          * one URI in the header field */
         LM_DBG("The last route URI: '%.*s'\n",
rt->nameaddr.uri.len,
                 ZSW(rt->nameaddr.uri.s));

         if (prev) {
             rem_off = prev->nameaddr.name.s + prev->len;
             rem_len = rt->nameaddr.name.s + rt->len - rem_off;
         } else {
             rem_off = hdr->name.s;
             rem_len = hdr->len;
         }
         if (!del_lump(_m, rem_off - _m->buf, rem_len, 0)) {
             LM_ERR("failed to remove Route HF\n");
             return RR_ERROR;
         }
     }

Therefore recover from previous strict routing is triggered: contents of 
request line is destroyed and 10.0.0.100 is put instead:
Apr 15 16:16:24 vpn-proxy oser[11027]: DBG:core:rewrite_uri: rewriting 
Request-URI with 
'sip:10.0.0.100;r2=on;lr;ftag=aa40c2a5-54fb-1810-970d-0015c5bf2da5'
Apr 15 16:16:24 vpn-proxy oser[11032]: [1] Got in dialog request not 
catched by loose_route(): BYE 
sip:10.0.0.100;r2=on;lr;ftag=aa40c2a5-54fb-1810-970d-0015c5bf2da5 
SIP/2.0^M Via:...

And we respond with 404 to in-dialog requests not caught by 
loose_route(). Previous hop is SER and I don't know why OpenSER 
considered it a strict router. Looks like a peculiarity of ALG mode. 
Please advice what should I do to solve this problem. Is it a 
configuration issue or perhaps loose_route() should not call 
after_strict() in case of double record-routing?

--
Thank you,
Andrew Pogrebennyk