resolved: when using the ResolveRecord() bus call, adjust TTL for caching time

When we return the full RR wire data, let's make sure the TTL included in it is
adjusted by the time the RR sat in the cache.

As an optimization we do this only for ResolveRecord() and not for
ResolveHostname() and friends, since adjusting the TTL means copying the RR
object, and we don#t want to do that if there's no reason to.
(ResolveHostname() and friends don't return the TTL hence there's no reason to
in that case)

10 files changed, 297 insertions, 5 deletions

diff --git a/src/resolve/resolved-bus.c b/src/resolve/resolved-bus.c
index 1f7883c067..2ca65e6953 100644
--- a/src/resolve/resolved-bus.c
+++ b/src/resolve/resolved-bus.c
@@ -672,6 +672,10 @@ static int bus_method_resolve_record(sd_bus_message *message, void *userdata, sd
         if (r < 0)
                 return r;
 
+        /* Let's request that the TTL is fixed up for locally cached entries, after all we return it in the wire format
+         * blob */
+        q->clamp_ttl = true;
+
         q->request = sd_bus_message_ref(message);
         q->complete = bus_method_resolve_record_complete;
 
diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
index 77c42d7aad..0bb5a95188 100644
--- a/src/resolve/resolved-dns-cache.c
+++ b/src/resolve/resolved-dns-cache.c
@@ -790,7 +790,7 @@ static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, D
         return NULL;
 }
 
-int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **ret, bool *authenticated) {
+int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcode, DnsAnswer **ret, bool *authenticated) {
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
         char key_str[DNS_RESOURCE_KEY_STRING_MAX];
         unsigned n = 0;
@@ -798,6 +798,7 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         bool nxdomain = false;
         DnsCacheItem *j, *first, *nsec = NULL;
         bool have_authenticated = false, have_non_authenticated = false;
+        usec_t current;
 
         assert(c);
         assert(key);
@@ -892,11 +893,24 @@ int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **r
         if (!answer)
                 return -ENOMEM;
 
+        if (clamp_ttl)
+                current = now(clock_boottime_or_monotonic());
+
         LIST_FOREACH(by_key, j, first) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
                 if (!j->rr)
                         continue;
 
-                r = dns_answer_add(answer, j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
+                if (clamp_ttl) {
+                        rr = dns_resource_record_ref(j->rr);
+
+                        r = dns_resource_record_clamp_ttl(&rr, LESS_BY(j->until, current) / USEC_PER_SEC);
+                        if (r < 0)
+                                return r;
+                }
+
+                r = dns_answer_add(answer, rr ?: j->rr, j->ifindex, j->authenticated ? DNS_ANSWER_AUTHENTICATED : 0);
                 if (r < 0)
                         return r;
         }
diff --git a/src/resolve/resolved-dns-cache.h b/src/resolve/resolved-dns-cache.h
index 2293718e86..22a7c17377 100644
--- a/src/resolve/resolved-dns-cache.h
+++ b/src/resolve/resolved-dns-cache.h
@@ -40,7 +40,7 @@ void dns_cache_flush(DnsCache *c);
 void dns_cache_prune(DnsCache *c);
 
 int dns_cache_put(DnsCache *c, DnsResourceKey *key, int rcode, DnsAnswer *answer, bool authenticated, uint32_t nsec_ttl, usec_t timestamp, int owner_family, const union in_addr_union *owner_address);
-int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, int *rcode, DnsAnswer **answer, bool *authenticated);
+int dns_cache_lookup(DnsCache *c, DnsResourceKey *key, bool clamp_ttl, int *rcode, DnsAnswer **answer, bool *authenticated);
 
 int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_family, const union in_addr_union *owner_address);
 
diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
index ea04e58d61..8578774c37 100644
--- a/src/resolve/resolved-dns-query.c
+++ b/src/resolve/resolved-dns-query.c
@@ -154,6 +154,7 @@ static int dns_query_candidate_add_transaction(DnsQueryCandidate *c, DnsResource
                 goto gc;
         }
 
+        t->clamp_ttl = c->query->clamp_ttl;
         return 1;
 
 gc:
@@ -420,7 +421,8 @@ int dns_query_new(
                 DnsQuery **ret,
                 DnsQuestion *question_utf8,
                 DnsQuestion *question_idna,
-                int ifindex, uint64_t flags) {
+                int ifindex,
+                uint64_t flags) {
 
         _cleanup_(dns_query_freep) DnsQuery *q = NULL;
         DnsResourceKey *key;
diff --git a/src/resolve/resolved-dns-query.h b/src/resolve/resolved-dns-query.h
index c2ac02f68b..53f48d462b 100644
--- a/src/resolve/resolved-dns-query.h
+++ b/src/resolve/resolved-dns-query.h
@@ -71,6 +71,10 @@ struct DnsQuery {
          * family */
         bool suppress_unroutable_family;
 
+
+        /* If true, the RR TTLs of the answer will be clamped by their current left validity in the cache */
+        bool clamp_ttl;
+
         DnsTransactionState state;
         unsigned n_cname_redirects;
 
diff --git a/src/resolve/resolved-dns-rr.c b/src/resolve/resolved-dns-rr.c
index 6a29a93a26..5687588a7d 100644
--- a/src/resolve/resolved-dns-rr.c
+++ b/src/resolve/resolved-dns-rr.c
@@ -1532,6 +1532,232 @@ const struct hash_ops dns_resource_record_hash_ops = {
         .compare = dns_resource_record_compare_func,
 };
 
+DnsResourceRecord *dns_resource_record_copy(DnsResourceRecord *rr) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *copy = NULL;
+        DnsResourceRecord *t;
+
+        assert(rr);
+
+        copy = dns_resource_record_new(rr->key);
+        if (!copy)
+                return NULL;
+
+        copy->ttl = rr->ttl;
+        copy->expiry = rr->expiry;
+        copy->n_skip_labels_signer = rr->n_skip_labels_signer;
+        copy->n_skip_labels_source = rr->n_skip_labels_source;
+        copy->unparseable = rr->unparseable;
+
+        switch (rr->unparseable ? _DNS_TYPE_INVALID : rr->key->type) {
+
+        case DNS_TYPE_SRV:
+                copy->srv.priority = rr->srv.priority;
+                copy->srv.weight = rr->srv.weight;
+                copy->srv.port = rr->srv.port;
+                copy->srv.name = strdup(rr->srv.name);
+                if (!copy->srv.name)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_PTR:
+        case DNS_TYPE_NS:
+        case DNS_TYPE_CNAME:
+        case DNS_TYPE_DNAME:
+                copy->ptr.name = strdup(rr->ptr.name);
+                if (!copy->ptr.name)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_HINFO:
+                copy->hinfo.cpu = strdup(rr->hinfo.cpu);
+                if (!copy->hinfo.cpu)
+                        return NULL;
+
+                copy->hinfo.os = strdup(rr->hinfo.os);
+                if(!copy->hinfo.os)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_TXT:
+        case DNS_TYPE_SPF:
+                copy->txt.items = dns_txt_item_copy(rr->txt.items);
+                if (!copy->txt.items)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_A:
+                copy->a = rr->a;
+                break;
+
+        case DNS_TYPE_AAAA:
+                copy->aaaa = rr->aaaa;
+                break;
+
+        case DNS_TYPE_SOA:
+                copy->soa.mname = strdup(rr->soa.mname);
+                if (!copy->soa.mname)
+                        return NULL;
+                copy->soa.rname = strdup(rr->soa.rname);
+                if (!copy->soa.rname)
+                        return NULL;
+                copy->soa.serial = rr->soa.serial;
+                copy->soa.refresh = rr->soa.refresh;
+                copy->soa.retry = rr->soa.retry;
+                copy->soa.expire = rr->soa.expire;
+                copy->soa.minimum = rr->soa.minimum;
+                break;
+
+        case DNS_TYPE_MX:
+                copy->mx.priority = rr->mx.priority;
+                copy->mx.exchange = strdup(rr->mx.exchange);
+                if (!copy->mx.exchange)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_LOC:
+                copy->loc = rr->loc;
+                break;
+
+        case DNS_TYPE_SSHFP:
+                copy->sshfp.algorithm = rr->sshfp.algorithm;
+                copy->sshfp.fptype = rr->sshfp.fptype;
+                copy->sshfp.fingerprint = memdup(rr->sshfp.fingerprint, rr->sshfp.fingerprint_size);
+                if (!copy->sshfp.fingerprint)
+                        return NULL;
+                copy->sshfp.fingerprint_size = rr->sshfp.fingerprint_size;
+                break;
+
+        case DNS_TYPE_DNSKEY:
+                copy->dnskey.flags = rr->dnskey.flags;
+                copy->dnskey.protocol = rr->dnskey.protocol;
+                copy->dnskey.algorithm = rr->dnskey.algorithm;
+                copy->dnskey.key = memdup(rr->dnskey.key, rr->dnskey.key_size);
+                if (!copy->dnskey.key)
+                        return NULL;
+                copy->dnskey.key_size = rr->dnskey.key_size;
+                break;
+
+        case DNS_TYPE_RRSIG:
+                copy->rrsig.type_covered = rr->rrsig.type_covered;
+                copy->rrsig.algorithm = rr->rrsig.algorithm;
+                copy->rrsig.labels = rr->rrsig.labels;
+                copy->rrsig.original_ttl = rr->rrsig.original_ttl;
+                copy->rrsig.expiration = rr->rrsig.expiration;
+                copy->rrsig.inception = rr->rrsig.inception;
+                copy->rrsig.key_tag = rr->rrsig.key_tag;
+                copy->rrsig.signer = strdup(rr->rrsig.signer);
+                if (!copy->rrsig.signer)
+                        return NULL;
+                copy->rrsig.signature = memdup(rr->rrsig.signature, rr->rrsig.signature_size);
+                if (!copy->rrsig.signature)
+                        return NULL;
+                copy->rrsig.signature_size = rr->rrsig.signature_size;
+                break;
+
+        case DNS_TYPE_NSEC:
+                copy->nsec.next_domain_name = strdup(rr->nsec.next_domain_name);
+                if (!copy->nsec.next_domain_name)
+                        return NULL;
+                copy->nsec.types = bitmap_copy(rr->nsec.types);
+                if (!copy->nsec.types)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_DS:
+                copy->ds.key_tag = rr->ds.key_tag;
+                copy->ds.algorithm = rr->ds.algorithm;
+                copy->ds.digest_type = rr->ds.digest_type;
+                copy->ds.digest = memdup(rr->ds.digest, rr->ds.digest_size);
+                if (!copy->ds.digest)
+                        return NULL;
+                copy->ds.digest_size = rr->ds.digest_size;
+                break;
+
+        case DNS_TYPE_NSEC3:
+                copy->nsec3.algorithm = rr->nsec3.algorithm;
+                copy->nsec3.flags = rr->nsec3.flags;
+                copy->nsec3.iterations = rr->nsec3.iterations;
+                copy->nsec3.salt = memdup(rr->nsec3.salt, rr->nsec3.salt_size);
+                if (!copy->nsec3.salt)
+                        return NULL;
+                copy->nsec3.salt_size = rr->nsec3.salt_size;
+                copy->nsec3.next_hashed_name = memdup(rr->nsec3.next_hashed_name, rr->nsec3.next_hashed_name_size);
+                if (!copy->nsec3.next_hashed_name_size)
+                        return NULL;
+                copy->nsec3.next_hashed_name_size = rr->nsec3.next_hashed_name_size;
+                copy->nsec3.types = bitmap_copy(rr->nsec3.types);
+                if (!copy->nsec3.types)
+                        return NULL;
+                break;
+
+        case DNS_TYPE_TLSA:
+                copy->tlsa.cert_usage = rr->tlsa.cert_usage;
+                copy->tlsa.selector = rr->tlsa.selector;
+                copy->tlsa.matching_type = rr->tlsa.matching_type;
+                copy->tlsa.data = memdup(rr->tlsa.data, rr->tlsa.data_size);
+                if (!copy->tlsa.data)
+                        return NULL;
+                copy->tlsa.data_size = rr->tlsa.data_size;
+                break;
+
+        case DNS_TYPE_CAA:
+                copy->caa.flags = rr->caa.flags;
+                copy->caa.tag = strdup(rr->caa.tag);
+                if (!copy->caa.tag)
+                        return NULL;
+                copy->caa.value = memdup(rr->caa.value, rr->caa.value_size);
+                if (!copy->caa.value)
+                        return NULL;
+                copy->caa.value_size = rr->caa.value_size;
+                break;
+
+        case DNS_TYPE_OPT:
+        default:
+                copy->generic.data = memdup(rr->generic.data, rr->generic.data_size);
+                if (!copy->generic.data)
+                        return NULL;
+                copy->generic.data_size = rr->generic.data_size;
+                break;
+        }
+
+        t = copy;
+        copy = NULL;
+
+        return t;
+}
+
+int dns_resource_record_clamp_ttl(DnsResourceRecord **rr, uint32_t max_ttl) {
+        DnsResourceRecord *old_rr, *new_rr;
+        uint32_t new_ttl;
+
+        assert(rr);
+        old_rr = *rr;
+
+        if (old_rr->key->type == DNS_TYPE_OPT)
+                return -EINVAL;
+
+        new_ttl = MIN(old_rr->ttl, max_ttl);
+        if (new_ttl == old_rr->ttl)
+                return 0;
+
+        if (old_rr->n_ref == 1) {
+                /* Patch in place */
+                old_rr->ttl = new_ttl;
+                return 1;
+        }
+
+        new_rr = dns_resource_record_copy(old_rr);
+        if (!new_rr)
+                return -ENOMEM;
+
+        new_rr->ttl = new_ttl;
+
+        dns_resource_record_unref(*rr);
+        *rr = new_rr;
+
+        return 1;
+}
+
 DnsTxtItem *dns_txt_item_free_all(DnsTxtItem *i) {
         DnsTxtItem *n;
 
@@ -1564,6 +1790,25 @@ bool dns_txt_item_equal(DnsTxtItem *a, DnsTxtItem *b) {
         return dns_txt_item_equal(a->items_next, b->items_next);
 }
 
+DnsTxtItem *dns_txt_item_copy(DnsTxtItem *first) {
+        DnsTxtItem *i, *copy = NULL, *end = NULL;
+
+        LIST_FOREACH(items, i, first) {
+                DnsTxtItem *j;
+
+                j = memdup(i, offsetof(DnsTxtItem, data) + i->length + 1);
+                if (!j) {
+                        dns_txt_item_free_all(copy);
+                        return NULL;
+                }
+
+                LIST_INSERT_AFTER(items, copy, end, j);
+                end = j;
+        }
+
+        return copy;
+}
+
 static const char* const dnssec_algorithm_table[_DNSSEC_ALGORITHM_MAX_DEFINED] = {
         /* Mnemonics as listed on https://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml */
         [DNSSEC_ALGORITHM_RSAMD5]             = "RSAMD5",
diff --git a/src/resolve/resolved-dns-rr.h b/src/resolve/resolved-dns-rr.h
index 020a2abd77..8b2d4df9e7 100644
--- a/src/resolve/resolved-dns-rr.h
+++ b/src/resolve/resolved-dns-rr.h
@@ -318,6 +318,7 @@ int dns_resource_record_new_reverse(DnsResourceRecord **ret, int family, const u
 int dns_resource_record_new_address(DnsResourceRecord **ret, int family, const union in_addr_union *address, const char *name);
 int dns_resource_record_equal(const DnsResourceRecord *a, const DnsResourceRecord *b);
 const char* dns_resource_record_to_string(DnsResourceRecord *rr);
+DnsResourceRecord *dns_resource_record_copy(DnsResourceRecord *rr);
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsResourceRecord*, dns_resource_record_unref);
 
 int dns_resource_record_to_wire_format(DnsResourceRecord *rr, bool canonical);
@@ -327,8 +328,11 @@ int dns_resource_record_source(DnsResourceRecord *rr, const char **ret);
 int dns_resource_record_is_signer(DnsResourceRecord *rr, const char *zone);
 int dns_resource_record_is_synthetic(DnsResourceRecord *rr);
 
+int dns_resource_record_clamp_ttl(DnsResourceRecord **rr, uint32_t max_ttl);
+
 DnsTxtItem *dns_txt_item_free_all(DnsTxtItem *i);
 bool dns_txt_item_equal(DnsTxtItem *a, DnsTxtItem *b);
+DnsTxtItem *dns_txt_item_copy(DnsTxtItem *i);
 
 void dns_resource_record_hash_func(const void *i, struct siphash *state);
 
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index bcb1b6d8a7..2d1767be0a 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -1274,7 +1274,7 @@ static int dns_transaction_prepare(DnsTransaction *t, usec_t ts) {
                 /* Let's then prune all outdated entries */
                 dns_cache_prune(&t->scope->cache);
 
-                r = dns_cache_lookup(&t->scope->cache, t->key, &t->answer_rcode, &t->answer, &t->answer_authenticated);
+                r = dns_cache_lookup(&t->scope->cache, t->key, t->clamp_ttl, &t->answer_rcode, &t->answer, &t->answer_authenticated);
                 if (r < 0)
                         return r;
                 if (r > 0) {
diff --git a/src/resolve/resolved-dns-transaction.h b/src/resolve/resolved-dns-transaction.h
index eaece91533..46a934a39b 100644
--- a/src/resolve/resolved-dns-transaction.h
+++ b/src/resolve/resolved-dns-transaction.h
@@ -74,6 +74,8 @@ struct DnsTransaction {
         bool initial_jitter_scheduled:1;
         bool initial_jitter_elapsed:1;
 
+        bool clamp_ttl:1;
+
         DnsPacket *sent, *received;
 
         DnsAnswer *answer;
diff --git a/src/resolve/test-dns-packet.c b/src/resolve/test-dns-packet.c
index 41e5c1caa5..956b155872 100644
--- a/src/resolve/test-dns-packet.c
+++ b/src/resolve/test-dns-packet.c
@@ -33,6 +33,19 @@
 
 #define HASH_KEY SD_ID128_MAKE(d3,1e,48,90,4b,fa,4c,fe,af,9d,d5,a1,d7,2e,8a,b1)
 
+static void verify_rr_copy(DnsResourceRecord *rr) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *copy = NULL;
+        const char *a, *b;
+
+        assert_se(copy = dns_resource_record_copy(rr));
+        assert_se(dns_resource_record_equal(copy, rr) > 0);
+
+        assert_se(a = dns_resource_record_to_string(rr));
+        assert_se(b = dns_resource_record_to_string(copy));
+
+        assert_se(streq(a, b));
+}
+
 static uint64_t hash(DnsResourceRecord *rr) {
         struct siphash state;
 
@@ -66,6 +79,8 @@ static void test_packet_from_file(const char* filename, bool canonical) {
                 assert_se(dns_packet_append_blob(p, data + offset + 8, packet_size, NULL) >= 0);
                 assert_se(dns_packet_read_rr(p, &rr, NULL, NULL) >= 0);
 
+                verify_rr_copy(rr);
+
                 s = dns_resource_record_to_string(rr);
                 assert_se(s);
                 puts(s);
@@ -78,6 +93,8 @@ static void test_packet_from_file(const char* filename, bool canonical) {
                 assert_se(dns_packet_append_blob(p2, rr->wire_format, rr->wire_format_size, NULL) >= 0);
                 assert_se(dns_packet_read_rr(p2, &rr2, NULL, NULL) >= 0);
 
+                verify_rr_copy(rr);
+
                 s2 = dns_resource_record_to_string(rr);
                 assert_se(s2);
                 assert_se(streq(s, s2));