dns_core.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2015, Digium, Inc.
 *
 * Joshua Colp <jcolp@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*! \file
 *
 * \brief Core DNS Functionality
 *
 * \author Joshua Colp <jcolp@digium.com>
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/_private.h"
#include "asterisk/linkedlists.h"
#include "asterisk/astobj2.h"
#include "asterisk/strings.h"
#include "asterisk/sched.h"
#include "asterisk/dns_core.h"
#include "asterisk/dns_srv.h"
#include "asterisk/dns_tlsa.h"
#include "asterisk/dns_recurring.h"
#include "asterisk/dns_resolver.h"
#include "asterisk/dns_internal.h"
#include "asterisk/netsock2.h"
 
#include <netinet/in.h>
#include <arpa/nameser.h>
 
AST_RWLIST_HEAD_STATIC(resolvers, ast_dns_resolver);
 
static struct ast_sched_context *sched;
 
struct ast_sched_context *ast_dns_get_sched(void)
{
    return sched;
}
 
const char *ast_dns_query_get_name(const struct ast_dns_query *query)
{
    return query->name;
}
 
int ast_dns_query_get_rr_type(const struct ast_dns_query *query)
{
    return query->rr_type;
}
 
int ast_dns_query_get_rr_class(const struct ast_dns_query *query)
{
    return query->rr_class;
}
 
void *ast_dns_query_get_data(const struct ast_dns_query *query)
{
    return query->user_data;
}
 
struct ast_dns_result *ast_dns_query_get_result(const struct ast_dns_query *query)
{
    return query->result;
}
 
unsigned int ast_dns_result_get_secure(const struct ast_dns_result *result)
{
    return result->secure;
}
 
unsigned int ast_dns_result_get_bogus(const struct ast_dns_result *result)
{
    return result->bogus;
}
 
unsigned int ast_dns_result_get_rcode(const struct ast_dns_result *result)
{
    return result->rcode;
}
 
const char *ast_dns_result_get_canonical(const struct ast_dns_result *result)
{
    return result->canonical;
}
 
const struct ast_dns_record *ast_dns_result_get_records(const struct ast_dns_result *result)
{
    return AST_LIST_FIRST(&result->records);
}
 
const char *ast_dns_result_get_answer(const struct ast_dns_result *result)
{
    return result->answer;
}
 
int ast_dns_result_get_lowest_ttl(const struct ast_dns_result *result)
{
    int ttl = 0;
    const struct ast_dns_record *record;
 
    if (ast_dns_result_get_rcode(result) == NXDOMAIN) {
        return 0;
    }
 
    for (record = ast_dns_result_get_records(result); record; record = ast_dns_record_get_next(record)) {
        if (!ttl || (ast_dns_record_get_ttl(record) && (ast_dns_record_get_ttl(record) < ttl))) {
            ttl = ast_dns_record_get_ttl(record);
        }
    }
 
    return ttl;
}
 
void ast_dns_result_free(struct ast_dns_result *result)
{
    struct ast_dns_record *record;
 
    if (!result) {
        return;
    }
 
    while ((record = AST_LIST_REMOVE_HEAD(&result->records, list))) {
        ast_free(record);
    }
 
    ast_free(result);
}
 
int ast_dns_record_get_rr_type(const struct ast_dns_record *record)
{
    return record->rr_type;
}
 
int ast_dns_record_get_rr_class(const struct ast_dns_record *record)
{
    return record->rr_class;
}
 
int ast_dns_record_get_ttl(const struct ast_dns_record *record)
{
    return record->ttl;
}
 
const char *ast_dns_record_get_data(const struct ast_dns_record *record)
{
    return record->data_ptr;
}
 
size_t ast_dns_record_get_data_size(const struct ast_dns_record *record)
{
    return record->data_len;
}
 
const struct ast_dns_record *ast_dns_record_get_next(const struct ast_dns_record *record)
{
    return AST_LIST_NEXT(record, list);
}
 
/*! \brief Destructor for an active DNS query */
static void dns_query_active_destroy(void *data)
{
    struct ast_dns_query_active *active = data;
 
    ao2_cleanup(active->query);
}
 
/*! \brief \brief Destructor for a DNS query */
static void dns_query_destroy(void *data)
{
    struct ast_dns_query *query = data;
 
    ao2_cleanup(query->user_data);
    ao2_cleanup(query->resolver_data);
    ast_dns_result_free(query->result);
}
 
struct ast_dns_query *dns_query_alloc(const char *name, int rr_type, int rr_class, ast_dns_resolve_callback callback, void *data)
{
    struct ast_dns_query *query;
 
    if (ast_strlen_zero(name)) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution, no name provided\n");
        return NULL;
    } else if (rr_type > 65536) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', resource record type '%d' exceeds maximum\n",
            name, rr_type);
        return NULL;
    } else if (rr_type < 0) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', invalid resource record type '%d'\n",
            name, rr_type);
        return NULL;
    } else if (rr_class > 65536) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', resource record class '%d' exceeds maximum\n",
            name, rr_class);
        return NULL;
    } else if (rr_class < 0) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', invalid resource class '%d'\n",
            name, rr_class);
        return NULL;
    } else if (!callback) {
        ast_log(LOG_WARNING, "Could not perform asynchronous resolution of '%s', no callback provided\n",
            name);
        return NULL;
    }
 
    query = ao2_alloc_options(sizeof(*query) + strlen(name) + 1, dns_query_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!query) {
        return NULL;
    }
 
    query->callback = callback;
    query->user_data = ao2_bump(data);
    query->rr_type = rr_type;
    query->rr_class = rr_class;
    strcpy(query->name, name); /* SAFE */
 
    AST_RWLIST_RDLOCK(&resolvers);
    query->resolver = AST_RWLIST_FIRST(&resolvers);
    AST_RWLIST_UNLOCK(&resolvers);
 
    if (!query->resolver) {
        ast_log(LOG_ERROR, "Attempted to do a DNS query for '%s' of class '%d' and type '%d' but no resolver is available\n",
            name, rr_class, rr_type);
        ao2_ref(query, -1);
        return NULL;
    }
 
    return query;
}
 
struct ast_dns_query_active *ast_dns_resolve_async(const char *name, int rr_type, int rr_class, ast_dns_resolve_callback callback, void *data)
{
    struct ast_dns_query_active *active;
 
    active = ao2_alloc_options(sizeof(*active), dns_query_active_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!active) {
        return NULL;
    }
 
    active->query = dns_query_alloc(name, rr_type, rr_class, callback, data);
    if (!active->query) {
        ao2_ref(active, -1);
        return NULL;
    }
 
    if (active->query->resolver->resolve(active->query)) {
        ast_log(LOG_ERROR, "Resolver '%s' returned an error when resolving '%s' of class '%d' and type '%d'\n",
            active->query->resolver->name, name, rr_class, rr_type);
        ao2_ref(active, -1);
        return NULL;
    }
 
    return active;
}
 
int ast_dns_resolve_cancel(struct ast_dns_query_active *active)
{
    return active->query->resolver->cancel(active->query);
}
 
/*! \brief Structure used for signaling back for synchronous resolution completion */
struct dns_synchronous_resolve {
    /*! \brief Lock used for signaling */
    ast_mutex_t lock;
    /*! \brief Condition used for signaling */
    ast_cond_t cond;
    /*! \brief Whether the query has completed */
    unsigned int completed;
    /*! \brief The result from the query */
    struct ast_dns_result *result;
};
 
/*! \brief Destructor for synchronous resolution structure */
static void dns_synchronous_resolve_destroy(void *data)
{
    struct dns_synchronous_resolve *synchronous = data;
 
    ast_mutex_destroy(&synchronous->lock);
    ast_cond_destroy(&synchronous->cond);
 
    /* This purposely does not unref result as it has been passed to the caller */
}
 
/*! \brief Callback used to implement synchronous resolution */
static void dns_synchronous_resolve_callback(const struct ast_dns_query *query)
{
    struct dns_synchronous_resolve *synchronous = ast_dns_query_get_data(query);
 
    synchronous->result = query->result;
    ((struct ast_dns_query *)query)->result = NULL;
 
    ast_mutex_lock(&synchronous->lock);
    synchronous->completed = 1;
    ast_cond_signal(&synchronous->cond);
    ast_mutex_unlock(&synchronous->lock);
}
 
int ast_dns_resolve(const char *name, int rr_type, int rr_class, struct ast_dns_result **result)
{
    struct dns_synchronous_resolve *synchronous;
    struct ast_dns_query_active *active;
 
    if (ast_strlen_zero(name)) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution, no name provided\n");
        return -1;
    } else if (rr_type > 65536) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', resource record type '%d' exceeds maximum\n",
            name, rr_type);
        return -1;
    } else if (rr_type < 0) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', invalid resource record type '%d'\n",
            name, rr_type);
        return -1;
    } else if (rr_class > 65536) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', resource record class '%d' exceeds maximum\n",
            name, rr_class);
        return -1;
    } else if (rr_class < 0) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', invalid resource class '%d'\n",
            name, rr_class);
        return -1;
    } else if (!result) {
        ast_log(LOG_WARNING, "Could not perform synchronous resolution of '%s', no result pointer provided for storing results\n",
            name);
        return -1;
    }
 
    synchronous = ao2_alloc_options(sizeof(*synchronous), dns_synchronous_resolve_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!synchronous) {
        return -1;
    }
 
    ast_mutex_init(&synchronous->lock);
    ast_cond_init(&synchronous->cond, NULL);
 
    active = ast_dns_resolve_async(name, rr_type, rr_class, dns_synchronous_resolve_callback, synchronous);
    if (active) {
        /* Wait for resolution to complete */
        ast_mutex_lock(&synchronous->lock);
        while (!synchronous->completed) {
            ast_cond_wait(&synchronous->cond, &synchronous->lock);
        }
        ast_mutex_unlock(&synchronous->lock);
        ao2_ref(active, -1);
    }
 
    *result = synchronous->result;
    ao2_ref(synchronous, -1);
 
    return *result ? 0 : -1;
}
 
int ast_dns_resolve_ipv6_and_ipv4(struct ast_sockaddr *address, const char *host, const char *port)
{
    RAII_VAR(struct ast_dns_query_set *, queries, ast_dns_query_set_create(), ao2_cleanup);
    int i;
    int rc;
 
    if (!queries) {
        ast_log(LOG_ERROR, "Couldn't allocate DNS query structure\n");
        return -1;
    }
    rc = ast_dns_query_set_add(queries, host, ns_t_aaaa, ns_c_in);
    if (rc != 0) {
        ast_log(LOG_ERROR, "Couldn't add 'AAAA' DNS query for '%s'\n", host);
        return -1;
    }
    rc = ast_dns_query_set_add(queries, host, ns_t_a, ns_c_in);
    if (rc != 0) {
        ast_log(LOG_ERROR, "Couldn't add 'A' DNS query for '%s'\n", host);
        return -1;
    }
    rc = ast_query_set_resolve(queries);
    if (rc != 0) {
        ast_log(LOG_ERROR, "Query set resolve failure for '%s'\n", host);
        return -1;
    }
    for (i = 0; i < ast_dns_query_set_num_queries(queries); ++i) {
        struct ast_dns_query *query = ast_dns_query_set_get(queries, i);
        struct ast_dns_result *result = ast_dns_query_get_result(query);
        const struct ast_dns_record *record;
        in_port_t in_port = 0;
 
        if (!ast_strlen_zero(port)) {
            in_port = htons(atoi(port));
        }
 
        for (record = ast_dns_result_get_records(result); record; record = ast_dns_record_get_next(record)) {
            size_t data_size = ast_dns_record_get_data_size(record);
            const unsigned char *data = (unsigned char *)ast_dns_record_get_data(record);
            int rr_type = ast_dns_record_get_rr_type(record);
 
            if (rr_type == ns_t_aaaa && data_size == 16) {
                struct sockaddr_in6 sin6 = { 0, };
 
                sin6.sin6_port = in_port;
                memcpy(&sin6.sin6_addr, data, data_size);
                sin6.sin6_family = AF_INET6;
                memcpy(&address->ss, &sin6, sizeof(sin6));
                address->len = sizeof(sin6);
 
                return 0;
            } else if (rr_type == ns_t_a && data_size == 4) {
                struct sockaddr_in sin4 = { 0, };
 
                sin4.sin_port = in_port;
                memcpy(&sin4.sin_addr, data, data_size);
                sin4.sin_family = AF_INET;
                memcpy(&address->ss, &sin4, sizeof(sin4));
                address->len = sizeof(sin4);
 
                return 0;
            } else {
                ast_debug(3, "Unrecognized rr_type '%u' or data_size '%zu' from DNS query for host '%s'\n",
                    rr_type, data_size, host);
                continue;
            }
        }
    }
 
    return -1;
}
 
int ast_dns_resolver_set_data(struct ast_dns_query *query, void *data)
{
    if (query->resolver_data) {
        return -1;
    }
 
    query->resolver_data = ao2_bump(data);
 
    return 0;
}
 
void *ast_dns_resolver_get_data(const struct ast_dns_query *query)
{
    return query->resolver_data;
}
 
int ast_dns_resolver_set_result(struct ast_dns_query *query, unsigned int secure, unsigned int bogus,
    unsigned int rcode, const char *canonical, const char *answer, size_t answer_size)
{
    char *buf_ptr;
 
    if (secure && bogus) {
        ast_debug(2, "Query '%p': Could not set result information, it can not be both secure and bogus\n",
            query);
        return -1;
    }
 
    if (ast_strlen_zero(canonical)) {
        ast_debug(2, "Query '%p': Could not set result information since no canonical name was provided\n",
            query);
        return -1;
    }
 
    if (!answer) {
        answer = "";
        answer_size = 0;
        ast_debug(2, "Query '%p': Assuming zero-sized answer on NULL input\n", query);
    }
 
    ast_dns_result_free(query->result);
 
    query->result = ast_calloc(1, sizeof(*query->result) + strlen(canonical) + 1 + answer_size);
    if (!query->result) {
        return -1;
    }
 
    query->result->secure = secure;
    query->result->bogus = bogus;
    query->result->rcode = rcode;
 
    buf_ptr = query->result->buf;
    strcpy(buf_ptr, canonical); /* SAFE */
    query->result->canonical = buf_ptr;
 
    buf_ptr += strlen(canonical) + 1;
    memcpy(buf_ptr, answer, answer_size); /* SAFE */
    query->result->answer = buf_ptr;
    query->result->answer_size = answer_size;
 
    return 0;
}
 
static struct ast_dns_record *generic_record_alloc(struct ast_dns_query *query, const char *data, const size_t size)
{
    struct ast_dns_record *record;
 
    record = ast_calloc(1, sizeof(*record) + size);
    if (!record) {
        return NULL;
    }
 
    record->data_ptr = record->data;
 
    return record;
}
 
typedef struct ast_dns_record *(*dns_alloc_fn)(struct ast_dns_query *query, const char *data, const size_t size);
 
static dns_alloc_fn dns_alloc_table [] = {
    [T_TXT]   = dns_txt_alloc,
    [T_NAPTR] = dns_naptr_alloc,
    [T_SRV]   = dns_srv_alloc,
};
 
static struct ast_dns_record *allocate_dns_record(unsigned int rr_type, struct ast_dns_query *query, const char *data, const size_t size)
{
    dns_alloc_fn allocator = generic_record_alloc;
 
    if (rr_type < ARRAY_LEN(dns_alloc_table) && dns_alloc_table[rr_type]) {
        allocator = dns_alloc_table[rr_type];
    }
 
    return allocator(query, data, size);
}
 
int ast_dns_resolver_add_record(struct ast_dns_query *query, int rr_type, int rr_class, int ttl, const char *data, const size_t size)
{
    struct ast_dns_record *record;
 
    if (rr_type < 0) {
        ast_debug(2, "Query '%p': Could not add record, invalid resource record type '%d'\n",
            query, rr_type);
        return -1;
    } else if (rr_type > 65536) {
        ast_debug(2, "Query '%p': Could not add record, resource record type '%d' exceeds maximum\n",
            query, rr_type);
        return -1;
    } else if (rr_class < 0) {
        ast_debug(2, "Query '%p': Could not add record, invalid resource record class '%d'\n",
            query, rr_class);
        return -1;
    } else if (rr_class > 65536) {
        ast_debug(2, "Query '%p': Could not add record, resource record class '%d' exceeds maximum\n",
            query, rr_class);
        return -1;
    } else if (ttl < 0) {
        ast_debug(2, "Query '%p': Could not add record, invalid TTL '%d'\n",
            query, ttl);
        return -1;
    } else if (!data || !size) {
        ast_debug(2, "Query '%p': Could not add record, no data specified\n",
            query);
        return -1;
    } else if (!query->result) {
        ast_debug(2, "Query '%p': No result was set on the query, thus records can not be added\n",
            query);
        return -1;
    }
 
    record = allocate_dns_record(rr_type, query, data, size);
    if (!record) {
        return -1;
    }
 
    record->rr_type = rr_type;
    record->rr_class = rr_class;
    record->ttl = ttl;
    record->data_len = size;
    memcpy(record->data_ptr, data, size);
 
    AST_LIST_INSERT_TAIL(&query->result->records, record, list);
 
    return 0;
}
 
typedef void (*dns_sort_fn)(struct ast_dns_result *result);
 
static dns_sort_fn dns_sort_table [] = {
    [T_NAPTR] = dns_naptr_sort,
    [T_SRV] = dns_srv_sort,
};
 
static void sort_result(int rr_type, struct ast_dns_result *result)
{
    if (dns_sort_table[rr_type]) {
        dns_sort_table[rr_type](result);
    }
}
 
void ast_dns_resolver_completed(struct ast_dns_query *query)
{
    if (query->result) {
        sort_result(ast_dns_query_get_rr_type(query), query->result);
    }
 
    query->callback(query);
}
 
static void dns_shutdown(void)
{
    if (sched) {
        ast_sched_context_destroy(sched);
        sched = NULL;
    }
}
 
int dns_core_init(void)
{
    sched = ast_sched_context_create();
    if (!sched) {
        return -1;
    }
 
    if (ast_sched_start_thread(sched)) {
        return -1;
    }
 
    ast_register_cleanup(dns_shutdown);
 
    return 0;
}
 
int ast_dns_resolver_register(struct ast_dns_resolver *resolver)
{
    struct ast_dns_resolver *iter;
    int inserted = 0;
 
    if (!resolver) {
        return -1;
    } else if (ast_strlen_zero(resolver->name)) {
        ast_log(LOG_ERROR, "Registration of DNS resolver failed as it does not have a name\n");
        return -1;
    } else if (!resolver->resolve) {
        ast_log(LOG_ERROR, "DNS resolver '%s' does not implement the resolve callback which is required\n",
            resolver->name);
        return -1;
    } else if (!resolver->cancel) {
        ast_log(LOG_ERROR, "DNS resolver '%s' does not implement the cancel callback which is required\n",
            resolver->name);
        return -1;
    }
 
    AST_RWLIST_WRLOCK(&resolvers);
 
    AST_LIST_TRAVERSE(&resolvers, iter, next) {
        if (!strcmp(iter->name, resolver->name)) {
            ast_log(LOG_ERROR, "A DNS resolver with the name '%s' is already registered\n", resolver->name);
            AST_RWLIST_UNLOCK(&resolvers);
            return -1;
        }
    }
 
    AST_RWLIST_TRAVERSE_SAFE_BEGIN(&resolvers, iter, next) {
        if (iter->priority > resolver->priority) {
            AST_RWLIST_INSERT_BEFORE_CURRENT(resolver, next);
            inserted = 1;
            break;
        }
    }
    AST_RWLIST_TRAVERSE_SAFE_END;
 
    if (!inserted) {
        AST_RWLIST_INSERT_TAIL(&resolvers, resolver, next);
    }
 
    AST_RWLIST_UNLOCK(&resolvers);
 
    ast_verb(5, "Registered DNS resolver '%s' with priority '%d'\n", resolver->name, resolver->priority);
 
    return 0;
}
 
void ast_dns_resolver_unregister(struct ast_dns_resolver *resolver)
{
    struct ast_dns_resolver *iter;
 
    if (!resolver) {
        return;
    }
 
    AST_RWLIST_WRLOCK(&resolvers);
    AST_RWLIST_TRAVERSE_SAFE_BEGIN(&resolvers, iter, next) {
        if (resolver == iter) {
            AST_RWLIST_REMOVE_CURRENT(next);
            break;
        }
    }
    AST_RWLIST_TRAVERSE_SAFE_END;
    AST_RWLIST_UNLOCK(&resolvers);
 
    ast_verb(5, "Unregistered DNS resolver '%s'\n", resolver->name);
}
 
char *dns_find_record(const char *record, size_t record_size, const char *response, size_t response_size)
{
    size_t remaining_size = response_size;
    const char *search_base = response;
    char *record_offset;
 
    while (1) {
        record_offset = memchr(search_base, record[0], remaining_size);
 
        ast_assert(record_offset != NULL);
        ast_assert(search_base + remaining_size - record_offset >= record_size);
 
        if (!memcmp(record_offset, record, record_size)) {
            return record_offset;
        }
 
        remaining_size -= record_offset - search_base;
        search_base = record_offset + 1;
    }
}
 
int dns_parse_short(unsigned char *cur, uint16_t *val)
{
    /* This assignment takes a big-endian 16-bit value and stores it in the
     * machine's native byte order. Using this method allows us to avoid potential
     * alignment issues in case the order is not on a short-addressable boundary.
     * See http://commandcenter.blogspot.com/2012/04/byte-order-fallacy.html for
     * more information
     */
    *val = (cur[1] << 0) | (cur[0] << 8);
    return sizeof(*val);
}
 
int dns_parse_string(char *cur, uint8_t *size, char **val)
{
    *size = *cur++;
    *val = cur;
    return *size + 1;
}