src/resolve/resolved-dns-answer.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <stdio.h>

#include "alloc-util.h"
#include "dns-domain.h"
#include "random-util.h"
#include "resolved-dns-answer.h"
#include "resolved-dns-dnssec.h"
#include "string-util.h"

static DnsAnswerItem *dns_answer_item_free(DnsAnswerItem *item) {
        if (!item)
                return NULL;

        dns_resource_record_unref(item->rr);
        dns_resource_record_unref(item->rrsig);

        return mfree(item);
}

DEFINE_PRIVATE_TRIVIAL_REF_UNREF_FUNC(DnsAnswerItem, dns_answer_item, dns_answer_item_free);
DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswerItem*, dns_answer_item_unref);

static void dns_answer_item_hash_func(const DnsAnswerItem *a, struct siphash *state) {
        assert(a);
        assert(state);

        siphash24_compress(&a->ifindex, sizeof(a->ifindex), state);

        dns_resource_record_hash_func(a->rr, state);
}

static int dns_answer_item_compare_func(const DnsAnswerItem *a, const DnsAnswerItem *b) {
        int r;

        assert(a);
        assert(b);

        r = CMP(a->ifindex, b->ifindex);
        if (r != 0)
                return r;

        return dns_resource_record_compare_func(a->rr, b->rr);
}

DEFINE_PRIVATE_HASH_OPS_WITH_KEY_DESTRUCTOR(
        dns_answer_item_hash_ops,
        DnsAnswerItem,
        dns_answer_item_hash_func,
        dns_answer_item_compare_func,
        dns_answer_item_unref);

static int dns_answer_reserve_internal(DnsAnswer *a, size_t n) {
        size_t m;

        assert(a);
        assert(a->items);

        m = ordered_set_size(a->items);
        assert(m <= UINT16_MAX); /* We can only place 64K RRs in an answer at max */

        n = saturate_add(m, n, UINT16_MAX);

        /* Higher multipliers give slightly higher efficiency through hash collisions, but the gains
         * quickly drop off after 2. */
        return ordered_set_reserve(a->items, n * 2);
}

DnsAnswer *dns_answer_new(size_t n) {
        _cleanup_ordered_set_free_ OrderedSet *s = NULL;
        _cleanup_(dns_answer_unrefp) DnsAnswer *a = NULL;

        if (n > UINT16_MAX)
                n = UINT16_MAX;

        s = ordered_set_new(&dns_answer_item_hash_ops);
        if (!s)
                return NULL;

        a = new(DnsAnswer, 1);
        if (!a)
                return NULL;

        *a = (DnsAnswer) {
                .n_ref = 1,
                .items = TAKE_PTR(s),
        };

        if (dns_answer_reserve_internal(a, n) < 0)
                return NULL;

        return TAKE_PTR(a);
}

static DnsAnswer *dns_answer_free(DnsAnswer *a) {
        assert(a);

        ordered_set_free(a->items);
        return mfree(a);
}

DEFINE_TRIVIAL_REF_UNREF_FUNC(DnsAnswer, dns_answer, dns_answer_free);

static int dns_answer_add_raw(
                DnsAnswer *a,
                DnsResourceRecord *rr,
                int ifindex,
                DnsAnswerFlags flags,
                DnsResourceRecord *rrsig) {

        _cleanup_(dns_answer_item_unrefp) DnsAnswerItem *item = NULL;
        int r;

        assert(rr);

        if (!a)
                return -ENOSPC;

        if (dns_answer_size(a) >= UINT16_MAX)
                return -ENOSPC;

        item = new(DnsAnswerItem, 1);
        if (!item)
                return -ENOMEM;

        *item = (DnsAnswerItem) {
                .n_ref = 1,
                .rr = dns_resource_record_ref(rr),
                .ifindex = ifindex,
                .flags = flags,
                .rrsig = dns_resource_record_ref(rrsig),
        };

        r = ordered_set_put(a->items, item);
        if (r < 0)
                return r;

        TAKE_PTR(item);
        return 1;
}

static int dns_answer_add_raw_all(DnsAnswer *a, DnsAnswer *source) {
        DnsAnswerItem *item;
        int r;

        DNS_ANSWER_FOREACH_ITEM(item, source) {
                r = dns_answer_add_raw(
                                a,
                                item->rr,
                                item->ifindex,
                                item->flags,
                                item->rrsig);
                if (r < 0)
                        return r;
        }

        return 0;
}

int dns_answer_add(
                DnsAnswer *a,
                DnsResourceRecord *rr,
                int ifindex,
                DnsAnswerFlags flags,
                DnsResourceRecord *rrsig) {

        DnsAnswerItem tmp, *exist;

        assert(rr);

        if (!a)
                return -ENOSPC;
        if (a->n_ref > 1)
                return -EBUSY;

        tmp = (DnsAnswerItem) {
                .rr = rr,
                .ifindex = ifindex,
        };

        exist = ordered_set_get(a->items, &tmp);
        if (exist) {
                /* There's already an RR of the same RRset in place! Let's see if the TTLs more or less
                 * match. We don't really care if they match precisely, but we do care whether one is 0 and
                 * the other is not. See RFC 2181, Section 5.2. */
                if ((rr->ttl == 0) != (exist->rr->ttl == 0))
                        return -EINVAL;

                /* Entry already exists, keep the entry with the higher TTL. */
                if (rr->ttl > exist->rr->ttl) {
                        DNS_RR_REPLACE(exist->rr, dns_resource_record_ref(rr));

                        /* Update RRSIG and RR at the same time */
                        if (rrsig)
                                DNS_RR_REPLACE(exist->rrsig, dns_resource_record_ref(rrsig));
                }

                exist->flags |= flags;

                if (rr->key->type == DNS_TYPE_RRSIG) {
                        /* If the rr is RRSIG, then move the rr to the end. */
                        assert_se(ordered_set_remove(a->items, exist) == exist);
                        assert_se(ordered_set_put(a->items, exist) == 1);
                }
                return 0;
        }

        return dns_answer_add_raw(a, rr, ifindex, flags, rrsig);
}

static int dns_answer_add_all(DnsAnswer *a, DnsAnswer *b) {
        DnsAnswerItem *item;
        int r;

        DNS_ANSWER_FOREACH_ITEM(item, b) {
                r = dns_answer_add(a, item->rr, item->ifindex, item->flags, item->rrsig);
                if (r < 0)
                        return r;
        }

        return 0;
}

int dns_answer_add_extend(
                DnsAnswer **a,
                DnsResourceRecord *rr,
                int ifindex,
                DnsAnswerFlags flags,
                DnsResourceRecord *rrsig) {

        int r;

        assert(a);
        assert(rr);

        r = dns_answer_reserve_or_clone(a, 1);
        if (r < 0)
                return r;

        return dns_answer_add(*a, rr, ifindex, flags, rrsig);
}

int dns_answer_add_soa(DnsAnswer *a, const char *name, uint32_t ttl, int ifindex) {
        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *soa = NULL;

        soa = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_SOA, name);
        if (!soa)
                return -ENOMEM;

        soa->ttl = ttl;

        soa->soa.mname = strdup(name);
        if (!soa->soa.mname)
                return -ENOMEM;

        soa->soa.rname = strjoin("root.", name);
        if (!soa->soa.rname)
                return -ENOMEM;

        soa->soa.serial = 1;
        soa->soa.refresh = 1;
        soa->soa.retry = 1;
        soa->soa.expire = 1;
        soa->soa.minimum = ttl;

        return dns_answer_add(a, soa, ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
}

int dns_answer_match_key(DnsAnswer *a, const DnsResourceKey *key, DnsAnswerFlags *ret_flags) {
        DnsAnswerFlags flags = 0, i_flags;
        DnsResourceRecord *i;
        bool found = false;
        int r;

        assert(key);

        DNS_ANSWER_FOREACH_FLAGS(i, i_flags, a) {
                r = dns_resource_key_match_rr(key, i, NULL);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                if (!ret_flags)
                        return 1;

                if (found)
                        flags &= i_flags;
                else {
                        flags = i_flags;
                        found = true;
                }
        }

        if (ret_flags)
                *ret_flags = flags;

        return found;
}

bool dns_answer_contains_nsec_or_nsec3(DnsAnswer *a) {
        DnsResourceRecord *i;

        DNS_ANSWER_FOREACH(i, a)
                if (IN_SET(i->key->type, DNS_TYPE_NSEC, DNS_TYPE_NSEC3))
                        return true;

        return false;
}

int dns_answer_contains_zone_nsec3(DnsAnswer *answer, const char *zone) {
        DnsResourceRecord *rr;
        int r;

        /* Checks whether the specified answer contains at least one NSEC3 RR in the specified zone */

        DNS_ANSWER_FOREACH(rr, answer) {
                const char *p;

                if (rr->key->type != DNS_TYPE_NSEC3)
                        continue;

                p = dns_resource_key_name(rr->key);
                r = dns_name_parent(&p);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                r = dns_name_equal(p, zone);
                if (r != 0)
                        return r;
        }

        return false;
}

bool dns_answer_contains(DnsAnswer *answer, DnsResourceRecord *rr) {
        DnsResourceRecord *i;

        DNS_ANSWER_FOREACH(i, answer)
                if (dns_resource_record_equal(i, rr))
                        return true;

        return false;
}

int dns_answer_find_soa(
                DnsAnswer *a,
                const DnsResourceKey *key,
                DnsResourceRecord **ret,
                DnsAnswerFlags *ret_flags) {

        DnsResourceRecord *rr, *soa = NULL;
        DnsAnswerFlags rr_flags, soa_flags = 0;
        int r;

        assert(key);

        /* For a SOA record we can never find a matching SOA record */
        if (key->type == DNS_TYPE_SOA)
                goto not_found;

        DNS_ANSWER_FOREACH_FLAGS(rr, rr_flags, a) {
                r = dns_resource_key_match_soa(key, rr->key);
                if (r < 0)
                        return r;
                if (r > 0) {

                        if (soa) {
                                r = dns_name_endswith(dns_resource_key_name(rr->key), dns_resource_key_name(soa->key));
                                if (r < 0)
                                        return r;
                                if (r > 0)
                                        continue;
                        }

                        soa = rr;
                        soa_flags = rr_flags;
                }
        }

        if (!soa)
                goto not_found;

        if (ret)
                *ret = soa;
        if (ret_flags)
                *ret_flags = soa_flags;

        return 1;

not_found:
        if (ret)
                *ret = NULL;
        if (ret_flags)
                *ret_flags = 0;

        return 0;
}

int dns_answer_find_cname_or_dname(
                DnsAnswer *a,
                const DnsResourceKey *key,
                DnsResourceRecord **ret,
                DnsAnswerFlags *ret_flags) {

        DnsResourceRecord *rr;
        DnsAnswerFlags rr_flags;
        int r;

        assert(key);

        /* For a {C,D}NAME record we can never find a matching {C,D}NAME record */
        if (!dns_type_may_redirect(key->type))
                return 0;

        DNS_ANSWER_FOREACH_FLAGS(rr, rr_flags, a) {
                r = dns_resource_key_match_cname_or_dname(key, rr->key, NULL);
                if (r < 0)
                        return r;
                if (r > 0) {
                        if (ret)
                                *ret = rr;
                        if (ret_flags)
                                *ret_flags = rr_flags;
                        return 1;
                }
        }

        if (ret)
                *ret = NULL;
        if (ret_flags)
                *ret_flags = 0;

        return 0;
}

int dns_answer_merge(DnsAnswer *a, DnsAnswer *b, DnsAnswer **ret) {
        _cleanup_(dns_answer_unrefp) DnsAnswer *k = NULL;
        int r;

        assert(ret);

        if (a == b) {
                *ret = dns_answer_ref(a);
                return 0;
        }

        if (dns_answer_size(a) <= 0) {
                *ret = dns_answer_ref(b);
                return 0;
        }

        if (dns_answer_size(b) <= 0) {
                *ret = dns_answer_ref(a);
                return 0;
        }

        k = dns_answer_new(dns_answer_size(a) + dns_answer_size(b));
        if (!k)
                return -ENOMEM;

        r = dns_answer_add_raw_all(k, a);
        if (r < 0)
                return r;

        r = dns_answer_add_all(k, b);
        if (r < 0)
                return r;

        *ret = TAKE_PTR(k);

        return 0;
}

int dns_answer_extend(DnsAnswer **a, DnsAnswer *b) {
        DnsAnswer *merged;
        int r;

        assert(a);

        r = dns_answer_merge(*a, b, &merged);
        if (r < 0)
                return r;

        DNS_ANSWER_REPLACE(*a, merged);
        return 0;
}

int dns_answer_remove_by_key(DnsAnswer **a, const DnsResourceKey *key) {
        DnsAnswerItem *item;
        bool found = false;
        int r;

        assert(a);
        assert(key);

        /* Remove all entries matching the specified key from *a */

        DNS_ANSWER_FOREACH_ITEM(item, *a) {
                r = dns_resource_key_equal(item->rr->key, key);
                if (r < 0)
                        return r;
                if (r > 0) {
                        dns_answer_item_unref(ordered_set_remove((*a)->items, item));
                        found = true;
                }
        }

        if (!found)
                return 0;

        if (dns_answer_isempty(*a))
                *a = dns_answer_unref(*a); /* Return NULL for the empty answer */

        return 1;
}

int dns_answer_remove_by_rr(DnsAnswer **a, DnsResourceRecord *rr) {
        _unused_ _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr_ref = dns_resource_record_ref(rr);
        DnsAnswerItem *item;
        bool found = false;
        int r;

        assert(a);
        assert(rr);

        /* Remove all entries matching the specified RR from *a */

        DNS_ANSWER_FOREACH_ITEM(item, *a) {
                r = dns_resource_record_equal(item->rr, rr);
                if (r < 0)
                        return r;
                if (r > 0) {
                        dns_answer_item_unref(ordered_set_remove((*a)->items, item));
                        found = true;
                }
        }

        if (!found)
                return 0;

        if (dns_answer_isempty(*a))
                *a = dns_answer_unref(*a); /* Return NULL for the empty answer */

        return 1;
}

int dns_answer_remove_by_answer_keys(DnsAnswer **a, DnsAnswer *b) {
        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *prev = NULL;
        DnsAnswerItem *item;
        int r;

        /* Removes all items from '*a' that have a matching key in 'b' */

        DNS_ANSWER_FOREACH_ITEM(item, b) {

                if (prev && dns_resource_key_equal(item->rr->key, prev)) /* Skip this one, we already looked at it */
                        continue;

                r = dns_answer_remove_by_key(a, item->rr->key);
                if (r < 0)
                        return r;
                if (!*a)
                        return 0; /* a is already empty. */

                /* Let's remember this entry's RR key, to optimize the loop a bit: if we have an RRset with
                 * more than one item then we don't need to remove the key multiple times */
                DNS_RESOURCE_KEY_REPLACE(prev, dns_resource_key_ref(item->rr->key));
        }

        return 0;
}

int dns_answer_copy_by_key(
                DnsAnswer **a,
                DnsAnswer *source,
                const DnsResourceKey *key,
                DnsAnswerFlags or_flags,
                DnsResourceRecord *rrsig) {

        DnsAnswerItem *item;
        int r;

        assert(a);
        assert(key);

        /* Copy all RRs matching the specified key from source into *a */

        DNS_ANSWER_FOREACH_ITEM(item, source) {

                r = dns_resource_key_equal(item->rr->key, key);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                r = dns_answer_add_extend(a, item->rr, item->ifindex, item->flags|or_flags, rrsig ?: item->rrsig);
                if (r < 0)
                        return r;
        }

        return 0;
}

int dns_answer_move_by_key(
                DnsAnswer **to,
                DnsAnswer **from,
                const DnsResourceKey *key,
                DnsAnswerFlags or_flags,
                DnsResourceRecord *rrsig) {

        int r;

        assert(to);
        assert(from);
        assert(key);

        r = dns_answer_copy_by_key(to, *from, key, or_flags, rrsig);
        if (r < 0)
                return r;

        return dns_answer_remove_by_key(from, key);
}

void dns_answer_order_by_scope(DnsAnswer *a, bool prefer_link_local) {
        _cleanup_free_ DnsAnswerItem **items = NULL;
        DnsAnswerItem **p, *item;
        size_t n;

        n = dns_answer_size(a);
        if (n <= 1)
                return;

        /* RFC 4795, Section 2.6 suggests we should order entries
         * depending on whether the sender is a link-local address. */

        p = items = new(DnsAnswerItem*, n);
        if (!items)
                return (void) log_oom();

        /* Order preferred address records and other records to the beginning of the array */
        DNS_ANSWER_FOREACH_ITEM(item, a)
                if (dns_resource_record_is_link_local_address(item->rr) == prefer_link_local)
                        *p++ = dns_answer_item_ref(item);

        /* Order address records that are not preferred to the end of the array */
        DNS_ANSWER_FOREACH_ITEM(item, a)
                if (dns_resource_record_is_link_local_address(item->rr) != prefer_link_local)
                        *p++ = dns_answer_item_ref(item);


        assert((size_t) (p - items) == n);

        ordered_set_clear(a->items);
        for (size_t i = 0; i < n; i++)
                assert_se(ordered_set_put(a->items, items[i]) >= 0);
}

int dns_answer_reserve(DnsAnswer **a, size_t n_free) {
        assert(a);

        if (n_free <= 0)
                return 0;

        if (!*a) {
                DnsAnswer *n;

                n = dns_answer_new(n_free);
                if (!n)
                        return -ENOMEM;

                *a = n;
                return 0;
        }

        if ((*a)->n_ref > 1)
                return -EBUSY;

        return dns_answer_reserve_internal(*a, n_free);
}

int dns_answer_reserve_or_clone(DnsAnswer **a, size_t n_free) {
        _cleanup_(dns_answer_unrefp) DnsAnswer *n = NULL;
        size_t ns;
        int r;

        assert(a);

        r = dns_answer_reserve(a, n_free);
        if (r != -EBUSY)
                return r;

        ns = dns_answer_size(*a);
        assert(ns <= UINT16_MAX); /* Maximum number of RRs we can stick into a DNS packet section */

        ns = saturate_add(ns, n_free, UINT16_MAX);

        n = dns_answer_new(ns);
        if (!n)
                return -ENOMEM;

        r = dns_answer_add_raw_all(n, *a);
        if (r < 0)
                return r;

        DNS_ANSWER_REPLACE(*a, TAKE_PTR(n));
        return 0;
}

/*
 * This function is not used in the code base, but is useful when debugging. Do not delete.
 */
void dns_answer_dump(DnsAnswer *answer, FILE *f) {
        DnsAnswerItem *item;

        if (!f)
                f = stdout;

        DNS_ANSWER_FOREACH_ITEM(item, answer) {
                const char *t;

                fputc('\t', f);

                t = dns_resource_record_to_string(item->rr);
                if (!t) {
                        log_oom();
                        continue;
                }

                fputs(t, f);
                fputs("\t;", f);
                fprintf(f, " ttl=%" PRIu32, item->rr->ttl);

                if (item->ifindex != 0)
                        fprintf(f, " ifindex=%i", item->ifindex);
                if (item->rrsig)
                        fputs(" rrsig", f);
                if (item->flags & DNS_ANSWER_AUTHENTICATED)
                        fputs(" authenticated", f);
                if (item->flags & DNS_ANSWER_CACHEABLE)
                        fputs(" cacheable", f);
                if (item->flags & DNS_ANSWER_SHARED_OWNER)
                        fputs(" shared-owner", f);
                if (item->flags & DNS_ANSWER_CACHE_FLUSH)
                        fputs(" cache-flush", f);
                if (item->flags & DNS_ANSWER_GOODBYE)
                        fputs(" goodbye", f);
                if (item->flags & DNS_ANSWER_SECTION_ANSWER)
                        fputs(" section-answer", f);
                if (item->flags & DNS_ANSWER_SECTION_AUTHORITY)
                        fputs(" section-authority", f);
                if (item->flags & DNS_ANSWER_SECTION_ADDITIONAL)
                        fputs(" section-additional", f);

                fputc('\n', f);
        }
}

int dns_answer_has_dname_for_cname(DnsAnswer *a, DnsResourceRecord *cname) {
        DnsResourceRecord *rr;
        int r;

        assert(cname);

        /* Checks whether the answer contains a DNAME record that indicates that the specified CNAME record is
         * synthesized from it */

        if (cname->key->type != DNS_TYPE_CNAME)
                return 0;

        DNS_ANSWER_FOREACH(rr, a) {
                _cleanup_free_ char *n = NULL;

                if (rr->key->type != DNS_TYPE_DNAME)
                        continue;
                if (rr->key->class != cname->key->class)
                        continue;

                r = dns_name_change_suffix(cname->cname.name, rr->dname.name, dns_resource_key_name(rr->key), &n);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                r = dns_name_equal(n, dns_resource_key_name(cname->key));
                if (r < 0)
                        return r;
                if (r > 0)
                        return 1;
        }

        return 0;
}

void dns_answer_randomize(DnsAnswer *a) {
        _cleanup_free_ DnsAnswerItem **items = NULL;
        DnsAnswerItem **p, *item;
        size_t n;

        /* Permutes the answer list randomly (Knuth shuffle) */

        n = dns_answer_size(a);
        if (n <= 1)
                return;

        p = items = new(DnsAnswerItem*, n);
        if (!items)
                return (void) log_oom();

        DNS_ANSWER_FOREACH_ITEM(item, a)
                *p++ = dns_answer_item_ref(item);

        assert((size_t) (p - items) == n);

        for (size_t i = 0; i < n; i++) {
                size_t k;

                k = random_u64_range(n);
                if (k == i)
                        continue;

                SWAP_TWO(items[i], items[k]);
        }

        ordered_set_clear(a->items);
        for (size_t i = 0; i < n; i++)
                assert_se(ordered_set_put(a->items, items[i]) >= 0);
}

uint32_t dns_answer_min_ttl(DnsAnswer *a) {
        uint32_t ttl = UINT32_MAX;
        DnsResourceRecord *rr;

        /* Return the smallest TTL of all RRs in this answer */

        DNS_ANSWER_FOREACH(rr, a) {
                /* Don't consider OPT (where the TTL field is used for other purposes than an actual TTL) */

                if (dns_type_is_pseudo(rr->key->type) ||
                    dns_class_is_pseudo(rr->key->class))
                        continue;

                ttl = MIN(ttl, rr->ttl);
        }

        return ttl;
}