add mDNS lookup method to libosmo-mslookup (#2)
Add the first actually useful lookup method to the mslookup library: multicast
DNS.
The server side is added in a subsequent commit, when the mslookup server is
implemented for the osmo-hlr program.
Use custom DNS encoding instead of libc-ares (which we use in OsmoSGSN
already), because libc-ares is only a DNS client implementation and we will
need both client and server.
Resubmit of f10463c5fc6d9e786ab7c648d99f7450f9a25906 after being
reverted in 110a49f69f29fed844d8743b76fd748f4a14812a. This new version
skips the mslookup_client_mdns test if multicast is not supported in the
build environment. I have verified that it doesn't break the build
anymore in my own OBS namespace.
Related: OS#4237, OS#4361
Patch-by: osmith, nhofmeyr
Change-Id: I3c340627181b632dd6a0d577aa2ea2a7cd035c0c
diff --git a/src/mslookup/mdns.c b/src/mslookup/mdns.c
new file mode 100644
index 0000000..4742a7c
--- /dev/null
+++ b/src/mslookup/mdns.c
@@ -0,0 +1,425 @@
+/* mslookup specific functions for encoding and decoding mslookup queries/results into mDNS packets, using the high
+ * level functions from mdns_msg.c and mdns_record.c to build the request/answer messages. */
+
+/* Copyright 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <osmocom/hlr/logging.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/mslookup/mslookup.h>
+#include <osmocom/mslookup/mdns_msg.h>
+#include <osmocom/mslookup/mdns_rfc.h>
+#include <errno.h>
+#include <inttypes.h>
+
+static struct msgb *osmo_mdns_msgb_alloc(const char *label)
+{
+ return msgb_alloc(1024, label);
+}
+
+/*! Combine the mslookup query service, ID and ID type into a domain string.
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. Example: "mdns.osmocom.org"
+ * \returns allocated buffer with the resulting domain (i.e. "sip.voice.123.msisdn.mdns.osmocom.org") on success,
+ * NULL on failure.
+ */
+static char *domain_from_query(void *ctx, const struct osmo_mslookup_query *query, const char *domain_suffix)
+{
+ const char *id;
+
+ /* Get id from query */
+ switch (query->id.type) {
+ case OSMO_MSLOOKUP_ID_IMSI:
+ id = query->id.imsi;
+ break;
+ case OSMO_MSLOOKUP_ID_MSISDN:
+ id = query->id.msisdn;
+ break;
+ default:
+ LOGP(DMSLOOKUP, LOGL_ERROR, "can't encode mslookup query id type %i", query->id.type);
+ return NULL;
+ }
+
+ return talloc_asprintf(ctx, "%s.%s.%s.%s", query->service, id, osmo_mslookup_id_type_name(query->id.type),
+ domain_suffix);
+}
+
+/*! Split up query service, ID and ID type from a domain string into a mslookup query.
+ * \param[in] domain with domain_suffix, e.g. "sip.voice.123.msisdn.mdns.osmocom.org"
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. It is not part of the resulting struct osmo_mslookup_query, so we
+ * remove it in this function. Example: "mdns.osmocom.org"
+ */
+int query_from_domain(struct osmo_mslookup_query *query, const char *domain, const char *domain_suffix)
+{
+ int domain_len = strlen(domain) - strlen(domain_suffix) - 1;
+ char domain_buf[OSMO_MDNS_RFC_MAX_NAME_LEN];
+
+ if (domain_len <= 0 || domain_len >= sizeof(domain_buf))
+ return -EINVAL;
+
+ if (domain[domain_len] != '.' || strcmp(domain + domain_len + 1, domain_suffix) != 0)
+ return -EINVAL;
+
+ memcpy(domain_buf, domain, domain_len);
+ domain_buf[domain_len] = '\0';
+ return osmo_mslookup_query_init_from_domain_str(query, domain_buf);
+}
+
+/*! Encode a mslookup query into a mDNS packet.
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. Example: "mdns.osmocom.org"
+ * \returns msgb, or NULL on error.
+ */
+struct msgb *osmo_mdns_query_encode(void *ctx, uint16_t packet_id, const struct osmo_mslookup_query *query,
+ const char *domain_suffix)
+{
+ struct osmo_mdns_msg_request req = {0};
+ struct msgb *msg = osmo_mdns_msgb_alloc(__func__);
+
+ req.id = packet_id;
+ req.type = OSMO_MDNS_RFC_RECORD_TYPE_ALL;
+ req.domain = domain_from_query(ctx, query, domain_suffix);
+ if (!req.domain)
+ goto error;
+ if (osmo_mdns_msg_request_encode(ctx, msg, &req))
+ goto error;
+ talloc_free(req.domain);
+ return msg;
+error:
+ msgb_free(msg);
+ talloc_free(req.domain);
+ return NULL;
+}
+
+/*! Decode a mDNS request packet into a mslookup query.
+ * \param[out] packet_id the result must be sent with the same packet_id.
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. Example: "mdns.osmocom.org"
+ * \returns allocated mslookup query on success, NULL on error.
+ */
+struct osmo_mslookup_query *osmo_mdns_query_decode(void *ctx, const uint8_t *data, size_t data_len,
+ uint16_t *packet_id, const char *domain_suffix)
+{
+ struct osmo_mdns_msg_request *req = NULL;
+ struct osmo_mslookup_query *query = NULL;
+
+ req = osmo_mdns_msg_request_decode(ctx, data, data_len);
+ if (!req)
+ return NULL;
+
+ query = talloc_zero(ctx, struct osmo_mslookup_query);
+ OSMO_ASSERT(query);
+ if (query_from_domain(query, req->domain, domain_suffix) < 0)
+ goto error_free;
+
+ *packet_id = req->id;
+ talloc_free(req);
+ return query;
+error_free:
+ talloc_free(req);
+ talloc_free(query);
+ return NULL;
+}
+
+/*! Parse sockaddr_str from mDNS record, so the mslookup result can be filled with it.
+ * \param[out] sockaddr_str resulting IPv4 or IPv6 sockaddr_str.
+ * \param[in] rec single record of the abstracted list of mDNS records
+ * \returns 0 on success, -EINVAL on error.
+ */
+static int sockaddr_str_from_mdns_record(struct osmo_sockaddr_str *sockaddr_str, struct osmo_mdns_record *rec)
+{
+ switch (rec->type) {
+ case OSMO_MDNS_RFC_RECORD_TYPE_A:
+ if (rec->length != 4) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "unexpected length of A record\n");
+ return -EINVAL;
+ }
+ osmo_sockaddr_str_from_32(sockaddr_str, *(uint32_t *)rec->data, 0);
+ break;
+ case OSMO_MDNS_RFC_RECORD_TYPE_AAAA:
+ if (rec->length != 16) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "unexpected length of AAAA record\n");
+ return -EINVAL;
+ }
+ osmo_sockaddr_str_from_in6_addr(sockaddr_str, (struct in6_addr*)rec->data, 0);
+ break;
+ default:
+ LOGP(DMSLOOKUP, LOGL_ERROR, "unexpected record type\n");
+ return -EINVAL;
+ }
+ return 0;
+}
+
+/*! Encode a successful mslookup result, along with the original query and packet_id into one mDNS answer packet.
+ *
+ * The records in the packet are ordered as follows:
+ * 1) "age", ip_v4/v6, "port" (only IPv4 or IPv6 present) or
+ * 2) "age", ip_v4, "port", ip_v6, "port" (both IPv4 and v6 present).
+ * "age" and "port" are TXT records, ip_v4 is an A record, ip_v6 is an AAAA record.
+ *
+ * \param[in] packet_id as received in osmo_mdns_query_decode().
+ * \param[in] query the original query, so we can send the domain back in the answer (i.e. "sip.voice.1234.msisdn").
+ * \param[in] result holds the age, IPs and ports of the queried service.
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. Example: "mdns.osmocom.org"
+ * \returns msg on success, NULL on error.
+ */
+struct msgb *osmo_mdns_result_encode(void *ctx, uint16_t packet_id, const struct osmo_mslookup_query *query,
+ const struct osmo_mslookup_result *result, const char *domain_suffix)
+{
+ struct osmo_mdns_msg_answer ans = {};
+ struct osmo_mdns_record *rec_age = NULL;
+ struct osmo_mdns_record rec_ip_v4 = {0};
+ struct osmo_mdns_record rec_ip_v6 = {0};
+ struct osmo_mdns_record *rec_ip_v4_port = NULL;
+ struct osmo_mdns_record *rec_ip_v6_port = NULL;
+ struct in_addr rec_ip_v4_in;
+ struct in6_addr rec_ip_v6_in;
+ struct msgb *msg = osmo_mdns_msgb_alloc(__func__);
+ char buf[256];
+
+ ctx = talloc_named(ctx, 0, "osmo_mdns_result_encode");
+
+ /* Prepare answer (ans) */
+ ans.domain = domain_from_query(ctx, query, domain_suffix);
+ if (!ans.domain)
+ goto error;
+ ans.id = packet_id;
+ INIT_LLIST_HEAD(&ans.records);
+
+ /* Record for age */
+ rec_age = osmo_mdns_record_txt_keyval_encode(ctx, "age", "%"PRIu32, result->age);
+ OSMO_ASSERT(rec_age);
+ llist_add_tail(&rec_age->list, &ans.records);
+
+ /* Records for IPv4 */
+ if (osmo_sockaddr_str_is_set(&result->host_v4)) {
+ if (osmo_sockaddr_str_to_in_addr(&result->host_v4, &rec_ip_v4_in) < 0) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "failed to encode ipv4: %s\n",
+ osmo_mslookup_result_name_b(buf, sizeof(buf), query, result));
+ goto error;
+ }
+ rec_ip_v4.type = OSMO_MDNS_RFC_RECORD_TYPE_A;
+ rec_ip_v4.data = (uint8_t *)&rec_ip_v4_in;
+ rec_ip_v4.length = sizeof(rec_ip_v4_in);
+ llist_add_tail(&rec_ip_v4.list, &ans.records);
+
+ rec_ip_v4_port = osmo_mdns_record_txt_keyval_encode(ctx, "port", "%"PRIu16, result->host_v4.port);
+ OSMO_ASSERT(rec_ip_v4_port);
+ llist_add_tail(&rec_ip_v4_port->list, &ans.records);
+ }
+
+ /* Records for IPv6 */
+ if (osmo_sockaddr_str_is_set(&result->host_v6)) {
+ if (osmo_sockaddr_str_to_in6_addr(&result->host_v6, &rec_ip_v6_in) < 0) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "failed to encode ipv6: %s\n",
+ osmo_mslookup_result_name_b(buf, sizeof(buf), query, result));
+ goto error;
+ }
+ rec_ip_v6.type = OSMO_MDNS_RFC_RECORD_TYPE_AAAA;
+ rec_ip_v6.data = (uint8_t *)&rec_ip_v6_in;
+ rec_ip_v6.length = sizeof(rec_ip_v6_in);
+ llist_add_tail(&rec_ip_v6.list, &ans.records);
+
+ rec_ip_v6_port = osmo_mdns_record_txt_keyval_encode(ctx, "port", "%"PRIu16, result->host_v6.port);
+ OSMO_ASSERT(rec_ip_v6_port);
+ llist_add_tail(&rec_ip_v6_port->list, &ans.records);
+ }
+
+ if (osmo_mdns_msg_answer_encode(ctx, msg, &ans)) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "failed to encode mDNS answer: %s\n",
+ osmo_mslookup_result_name_b(buf, sizeof(buf), query, result));
+ goto error;
+ }
+ talloc_free(ctx);
+ return msg;
+error:
+ msgb_free(msg);
+ talloc_free(ctx);
+ return NULL;
+}
+
+static int decode_uint32_t(const char *str, uint32_t *val)
+{
+ long long int lld;
+ char *endptr = NULL;
+ *val = 0;
+ errno = 0;
+ lld = strtoll(str, &endptr, 10);
+ if (errno || !endptr || *endptr)
+ return -EINVAL;
+ if (lld < 0 || lld > UINT32_MAX)
+ return -EINVAL;
+ *val = lld;
+ return 0;
+}
+
+static int decode_port(const char *str, uint16_t *port)
+{
+ uint32_t val;
+ if (decode_uint32_t(str, &val))
+ return -EINVAL;
+ if (val > 65535)
+ return -EINVAL;
+ *port = val;
+ return 0;
+}
+
+/*! Read expected mDNS records into mslookup result.
+ *
+ * The records in the packet must be ordered as follows:
+ * 1) "age", ip_v4/v6, "port" (only IPv4 or IPv6 present) or
+ * 2) "age", ip_v4, "port", ip_v6, "port" (both IPv4 and v6 present).
+ * "age" and "port" are TXT records, ip_v4 is an A record, ip_v6 is an AAAA record.
+ *
+ * \param[out] result holds the age, IPs and ports of the queried service.
+ * \param[in] ans abstracted mDNS answer with a list of resource records.
+ * \returns 0 on success, -EINVAL on error.
+ */
+int osmo_mdns_result_from_answer(struct osmo_mslookup_result *result, const struct osmo_mdns_msg_answer *ans)
+{
+ struct osmo_mdns_record *rec;
+ char txt_key[64];
+ char txt_value[64];
+ bool found_age = false;
+ bool found_ip_v4 = false;
+ bool found_ip_v6 = false;
+ struct osmo_sockaddr_str *expect_port_for = NULL;
+
+ *result = (struct osmo_mslookup_result){};
+
+ result->rc = OSMO_MSLOOKUP_RC_NONE;
+
+ llist_for_each_entry(rec, &ans->records, list) {
+ switch (rec->type) {
+ case OSMO_MDNS_RFC_RECORD_TYPE_A:
+ if (expect_port_for) {
+ LOGP(DMSLOOKUP, LOGL_ERROR,
+ "'A' record found, but still expecting a 'port' value first\n");
+ return -EINVAL;
+ }
+ if (found_ip_v4) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "'A' record found twice in mDNS answer\n");
+ return -EINVAL;
+ }
+ found_ip_v4 = true;
+ expect_port_for = &result->host_v4;
+ if (sockaddr_str_from_mdns_record(expect_port_for, rec)) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "'A' record with invalid address data\n");
+ return -EINVAL;
+ }
+ break;
+ case OSMO_MDNS_RFC_RECORD_TYPE_AAAA:
+ if (expect_port_for) {
+ LOGP(DMSLOOKUP, LOGL_ERROR,
+ "'AAAA' record found, but still expecting a 'port' value first\n");
+ return -EINVAL;
+ }
+ if (found_ip_v6) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "'AAAA' record found twice in mDNS answer\n");
+ return -EINVAL;
+ }
+ found_ip_v6 = true;
+ expect_port_for = &result->host_v6;
+ if (sockaddr_str_from_mdns_record(expect_port_for, rec) != 0) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "'AAAA' record with invalid address data\n");
+ return -EINVAL;
+ }
+ break;
+ case OSMO_MDNS_RFC_RECORD_TYPE_TXT:
+ if (osmo_mdns_record_txt_keyval_decode(rec, txt_key, sizeof(txt_key),
+ txt_value, sizeof(txt_value)) != 0) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "failed to decode txt record\n");
+ return -EINVAL;
+ }
+ if (strcmp(txt_key, "age") == 0) {
+ if (found_age) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "duplicate 'TXT' record for 'age'\n");
+ return -EINVAL;
+ }
+ found_age = true;
+ if (decode_uint32_t(txt_value, &result->age)) {
+ LOGP(DMSLOOKUP, LOGL_ERROR,
+ "'TXT' record: invalid 'age' value ('age=%s')\n", txt_value);
+ return -EINVAL;
+ }
+ } else if (strcmp(txt_key, "port") == 0) {
+ if (!expect_port_for) {
+ LOGP(DMSLOOKUP, LOGL_ERROR,
+ "'TXT' record for 'port' without previous 'A' or 'AAAA' record\n");
+ return -EINVAL;
+ }
+ if (decode_port(txt_value, &expect_port_for->port)) {
+ LOGP(DMSLOOKUP, LOGL_ERROR,
+ "'TXT' record: invalid 'port' value ('port=%s')\n", txt_value);
+ return -EINVAL;
+ }
+ expect_port_for = NULL;
+ } else {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "unexpected key '%s' in TXT record\n", txt_key);
+ return -EINVAL;
+ }
+ break;
+ default:
+ LOGP(DMSLOOKUP, LOGL_ERROR, "unexpected record type\n");
+ return -EINVAL;
+ }
+ }
+
+ /* Check if everything was found */
+ if (!found_age || !(found_ip_v4 || found_ip_v6) || expect_port_for) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "missing resource records in mDNS answer\n");
+ return -EINVAL;
+ }
+
+ result->rc = OSMO_MSLOOKUP_RC_RESULT;
+ return 0;
+}
+
+/*! Decode a mDNS answer packet into a mslookup result, query and packet_id.
+ * \param[out] packet_id same ID as sent in the request packet.
+ * \param[out] query the original query (service, ID, ID type).
+ * \param[out] result holds the age, IPs and ports of the queried service.
+ * \param[in] domain_suffix is appended to each domain in the queries to avoid colliding with the top-level domains
+ * administrated by IANA. Example: "mdns.osmocom.org"
+ * \returns 0 on success, -EINVAL on error.
+ */
+int osmo_mdns_result_decode(void *ctx, const uint8_t *data, size_t data_len, uint16_t *packet_id,
+ struct osmo_mslookup_query *query, struct osmo_mslookup_result *result,
+ const char *domain_suffix)
+{
+ int rc = -EINVAL;
+ struct osmo_mdns_msg_answer *ans;
+ ans = osmo_mdns_msg_answer_decode(ctx, data, data_len);
+ if (!ans)
+ goto exit_free;
+
+ if (query_from_domain(query, ans->domain, domain_suffix) < 0)
+ goto exit_free;
+
+ if (osmo_mdns_result_from_answer(result, ans) < 0)
+ goto exit_free;
+
+ *packet_id = ans->id;
+ rc = 0;
+
+exit_free:
+ talloc_free(ans);
+ return rc;
+}