sgsn: Allow to resolve the IPv4 address of a GGSN through DNS

For real networks we need to check if the requested APN string
is allowed and then resolve the GGSN address through DNS. There
are countries with two or three digit MNCs and one could either
try to keep a list of countries that have two/three digits or
just try both of them. I have opted for the later for the ease
of the implementation.

C-Ares doesn't allow to cancel a request so we will need to
have the MMCTX and the Lookup have different lifetimes. We simply
set ->mmctx to NULL in case the MMCTX dies more early.

The selected and verified apn_str will be copied into the out
parameter. In case no static APN/GGSN config is present and the
dynamic mode is enabled a request will be made.

1 files changed, 141 insertions, 10 deletions

diff --git a/openbsc/src/gprs/gprs_gmm.c b/openbsc/src/gprs/gprs_gmm.c
index d7ba5b4f5..07fd1dcfd 100644
--- a/openbsc/src/gprs/gprs_gmm.c
+++ b/openbsc/src/gprs/gprs_gmm.c
@@ -29,6 +29,7 @@
 
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <netdb.h>
 
 #include <openbsc/db.h>
 #include <osmocom/core/msgb.h>
@@ -37,6 +38,7 @@
 #include <osmocom/core/signal.h>
 #include <osmocom/core/talloc.h>
 #include <osmocom/core/rate_ctr.h>
+#include <osmocom/gsm/apn.h>
 
 #include <osmocom/gprs/gprs_bssgp.h>
 
@@ -1633,7 +1635,7 @@ int gsm48_tx_gsm_deact_pdp_acc(struct sgsn_pdp_ctx *pdp)
 static int activate_ggsn(struct sgsn_mm_ctx *mmctx,
 		struct sgsn_ggsn_ctx *ggsn, const uint8_t transaction_id,
 		const uint8_t req_nsapi, const uint8_t req_llc_sapi,
-		struct tlv_parsed *tp)
+		struct tlv_parsed *tp, int destroy_ggsn)
 {
 	struct sgsn_pdp_ctx *pdp;
 
@@ -1646,10 +1648,94 @@ static int activate_ggsn(struct sgsn_mm_ctx *mmctx,
 	/* Store SAPI and Transaction Identifier */
 	pdp->sapi = req_llc_sapi;
 	pdp->ti = transaction_id;
+	pdp->destroy_ggsn = destroy_ggsn;
 
 	return 0;
 }
 
+static void ggsn_lookup_cb(void *arg, int status, int timeouts, struct hostent *hostent)
+{
+	struct sgsn_ggsn_ctx *ggsn;
+	struct sgsn_ggsn_lookup *lookup = arg;
+	struct in_addr *addr = NULL;
+	int i;
+
+	/* The context is gone while we made a request */
+	if (!lookup->mmctx) {
+		talloc_free(lookup);
+		return;
+	}
+
+	if (status != ARES_SUCCESS) {
+		struct sgsn_mm_ctx *mmctx = lookup->mmctx;
+
+		LOGMMCTXP(LOGL_ERROR, mmctx, "DNS query failed.\n");
+
+		/* Need to try with three digits now */
+		if (lookup->state == SGSN_GGSN_2DIGIT) {
+			char *hostname;
+			int rc;
+
+			lookup->state = SGSN_GGSN_3DIGIT;
+			hostname = osmo_apn_qualify_from_imsi(mmctx->imsi,
+					lookup->apn_str, 1);
+			LOGMMCTXP(LOGL_DEBUG, mmctx,
+				"Going to query %s\n", hostname);
+			rc = sgsn_ares_query(sgsn, hostname,
+					ggsn_lookup_cb, lookup);
+			if (rc != 0) {
+				LOGP(DGPRS, LOGL_ERROR, "Couldn't start GGSN\n");
+				goto reject_due_failure;
+			}
+			return;
+		}
+
+		LOGMMCTXP(LOGL_ERROR, mmctx, "Couldn't resolve GGSN\n");
+		goto reject_due_failure;
+	}
+
+	if (hostent->h_length != sizeof(struct in_addr)) {
+		LOGMMCTXP(LOGL_ERROR, lookup->mmctx,
+			"Wrong addr size(%d)\n", sizeof(struct in_addr));
+		goto reject_due_failure;
+	}
+
+	/* get the address */
+	for (i = 0, addr = (struct in_addr *) hostent->h_addr_list[i]; addr;
+		i++, addr = (struct in_addr *) hostent->h_addr_list[i]) {
+		break;
+	}
+
+	if (!addr) {
+		LOGMMCTXP(LOGL_ERROR, lookup->mmctx, "No host address.\n");
+		goto reject_due_failure;
+	}
+
+	ggsn = sgsn_ggsn_ctx_alloc(UINT32_MAX);
+	if (!ggsn) {
+		LOGMMCTXP(LOGL_ERROR, lookup->mmctx, "Failed to create ggsn.\n");
+		goto reject_due_failure;
+	}
+	ggsn->remote_addr = *addr;
+	LOGMMCTXP(LOGL_NOTICE, lookup->mmctx,
+		"Selected %s as GGSN.\n", inet_ntoa(*addr));
+
+	/* forget about the ggsn look-up */
+	lookup->mmctx->ggsn_lookup = NULL;
+
+	activate_ggsn(lookup->mmctx, ggsn, lookup->ti, lookup->nsapi,
+			lookup->sapi, &lookup->tp, 1);
+
+	/* Now free it */
+	talloc_free(lookup);
+	return;
+
+reject_due_failure:
+	gsm48_tx_gsm_act_pdp_rej(lookup->mmctx, lookup->ti,
+				GMM_CAUSE_NET_FAIL, 0, NULL);
+	lookup->mmctx->ggsn_lookup = NULL;
+	talloc_free(lookup);
+}
 
 static int do_act_pdp_req(struct sgsn_mm_ctx *mmctx, struct msgb *msg)
 {
@@ -1662,6 +1748,9 @@ static int do_act_pdp_req(struct sgsn_mm_ctx *mmctx, struct msgb *msg)
 	struct sgsn_ggsn_ctx *ggsn;
 	struct sgsn_pdp_ctx *pdp;
 	enum gsm48_gsm_cause gsm_cause;
+	char apn_str[GSM_APN_LENGTH] = { 0, };
+	char *hostname;
+	int rc;
 
 	LOGMMCTXP(LOGL_INFO, mmctx, "-> ACTIVATE PDP CONTEXT REQ: SAPI=%u NSAPI=%u ",
 		act_req->req_llc_sapi, act_req->req_nsapi);
@@ -1746,22 +1835,64 @@ static int do_act_pdp_req(struct sgsn_mm_ctx *mmctx, struct msgb *msg)
 						0, NULL);
 	}
 
+	if (mmctx->ggsn_lookup) {
+		if (mmctx->ggsn_lookup->sapi == act_req->req_llc_sapi &&
+			mmctx->ggsn_lookup->ti == transaction_id) {
+			LOGMMCTXP(LOGL_NOTICE, mmctx,
+				"Re-transmission while doing look-up. Ignoring.\n");
+			return 0;
+		}
+	}
+
 	/* Only increment counter for a real activation, after we checked
 	 * for re-transmissions */
 	rate_ctr_inc(&mmctx->ctrg->ctr[GMM_CTR_PDP_CTX_ACT]);
 
 	/* Determine GGSN based on APN and subscription options */
-	ggsn = sgsn_mm_ctx_find_ggsn_ctx(mmctx, &tp, &gsm_cause);
-	if (!ggsn) {
-		LOGP(DGPRS, LOGL_ERROR, "No GGSN context found!\n");
-		return gsm48_tx_gsm_act_pdp_rej(mmctx, transaction_id,
-						gsm_cause, 0, NULL);
+	ggsn = sgsn_mm_ctx_find_ggsn_ctx(mmctx, &tp, &gsm_cause, apn_str);
+	if (ggsn)
+		return activate_ggsn(mmctx, ggsn, transaction_id,
+				act_req->req_nsapi, act_req->req_llc_sapi,
+				&tp, 0);
+
+	if (strlen(apn_str) == 0)
+		goto no_context;
+	if (!sgsn->cfg.dynamic_lookup)
+		goto no_context;
+
+	/* schedule a dynamic look-up */
+	mmctx->ggsn_lookup = talloc_zero(tall_bsc_ctx, struct sgsn_ggsn_lookup);
+	if (!mmctx->ggsn_lookup)
+		goto no_context;
+
+	mmctx->ggsn_lookup->state = SGSN_GGSN_2DIGIT;
+	mmctx->ggsn_lookup->mmctx = mmctx;
+	strcpy(mmctx->ggsn_lookup->apn_str, apn_str);
+
+	mmctx->ggsn_lookup->orig_msg = msg;
+	mmctx->ggsn_lookup->tp = tp;
+
+	mmctx->ggsn_lookup->ti = transaction_id;
+	mmctx->ggsn_lookup->nsapi = act_req->req_nsapi;
+	mmctx->ggsn_lookup->sapi = act_req->req_llc_sapi;
+
+	hostname = osmo_apn_qualify_from_imsi(mmctx->imsi,
+				mmctx->ggsn_lookup->apn_str, 0);
+
+	LOGMMCTXP(LOGL_DEBUG, mmctx, "Going to query %s\n", hostname);
+	rc = sgsn_ares_query(sgsn, hostname,
+				ggsn_lookup_cb, mmctx->ggsn_lookup);
+	if (rc != 0) {
+		LOGMMCTXP(LOGL_ERROR, mmctx, "Failed to start ares query.\n");
+		goto no_context;
 	}
 
-	/* Now activate the GGSN */
-	return activate_ggsn(mmctx, ggsn, transaction_id,
-				act_req->req_nsapi, act_req->req_llc_sapi,
-				&tp);
+	return 0;
+
+no_context:
+	LOGP(DGPRS, LOGL_ERROR, "No GGSN context found!\n");
+	return gsm48_tx_gsm_act_pdp_rej(mmctx, transaction_id,
+					gsm_cause, 0, NULL);
 }
 
 /* Section 9.5.1: Activate PDP Context Request */