Assorted resolved hardening fixes flagged by kres (#43011)

src/resolve/resolved-dns-browse-services.c

@@ -178,8 +178,8 @@ int dns_add_new_service(DnsServiceBrowser *sb, DnsResourceRecord *rr, int owner_
                 .query = NULL,
                 .rr_ttl_state = DNS_RECORD_TTL_STATE_80_PERCENT,
         };
-
-        LIST_PREPEND(dns_services, sb->dns_services, s);
+        if (!s->rr)
+                return log_oom();
 
         /* Schedule the first cache maintenance query at 80% of the record's
          * TTL. Subsequent queries issued at 5% increments until 100% of the
@@ -219,6 +219,8 @@ int dns_add_new_service(DnsServiceBrowser *sb, DnsResourceRecord *rr, int owner_
                                 r,
                                 "Failed to schedule mDNS maintenance query for DNS service: %m");
 
+        LIST_PREPEND(dns_services, sb->dns_services, s);
+
         TAKE_PTR(s);
         return 0;
 }

src/resolve/resolved-dns-zone.c

@@ -161,8 +161,15 @@ static int dns_zone_link_item(DnsZone *z, DnsZoneItem *i) {
                 assert_se(hashmap_replace(z->by_name, dns_resource_key_name(first->rr->key), first) >= 0);
         } else {
                 r = hashmap_put(z->by_name, dns_resource_key_name(i->rr->key), i);
-                if (r < 0)
+                if (r < 0) {
+                        first = hashmap_get(z->by_key, i->rr->key);
+                        LIST_REMOVE(by_key, first, i);
+                        if (first)
+                                assert_se(hashmap_replace(z->by_key, first->rr->key, first) >= 0);
+                        else
+                                hashmap_remove(z->by_key, i->rr->key);
                         return r;
+                }
         }
 
         return 0;

src/resolve/test-dns-answer.c

@@ -371,6 +371,23 @@ TEST(dns_answer_remove_by_rr) {
         ASSERT_NULL(answer);
 }
 
+TEST(dns_answer_remove_shared) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = prepare_answer(), *alias = NULL;
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+        alias = dns_answer_ref(answer);
+        ASSERT_PTR_EQ(alias, answer);
+
+        rr = ASSERT_NOT_NULL(dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, "b.example.com"));
+        rr->a.in_addr.s_addr = htobe32(0xc0a8017f);
+
+        ASSERT_OK_POSITIVE(dns_answer_remove_by_rr(&answer, rr));
+        ASSERT_EQ(dns_answer_size(answer), 2u);
+        ASSERT_EQ(dns_answer_size(alias), 3u);
+        ASSERT_FALSE(dns_answer_contains(answer, rr));
+        ASSERT_TRUE(dns_answer_contains(alias, rr));
+}
+
 TEST(dns_answer_remove_by_answer_keys) {
         _cleanup_(dns_answer_unrefp) DnsAnswer *a = prepare_answer(), *b = prepare_answer();
         DnsResourceKey *key;

src/shared/dns-answer.c

@@ -555,14 +555,28 @@ int dns_answer_remove_by_rr(DnsAnswer **a, DnsResourceRecord *rr) {
                 if (r < 0)
                         return r;
                 if (r > 0) {
-                        dns_answer_item_unref(ordered_set_remove((*a)->items, item));
                         found = true;
+                        break;
                 }
         }
 
         if (!found)
                 return 0;
 
+        if ((*a)->n_ref > 1) {
+                r = dns_answer_reserve_or_clone(a, 1);
+                if (r < 0)
+                        return r;
+        }
+
+        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));
+        }
+
         if (dns_answer_isempty(*a))
                 *a = dns_answer_unref(*a); /* Return NULL for the empty answer */