4 files changed, 55 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
index 2179a61890..6124ff659c 100644
--- a/src/resolve/resolved-dns-cache.c
+++ b/src/resolve/resolved-dns-cache.c
@@ -731,6 +731,39 @@ int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_
         return 1;
 }
 
+int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p) {
+        unsigned ancount = 0;
+        Iterator iterator;
+        DnsCacheItem *i;
+        int r;
+
+        assert(cache);
+
+        HASHMAP_FOREACH(i, cache->by_key, iterator) {
+                DnsCacheItem *j;
+
+                LIST_FOREACH(by_key, j, i) {
+                        _cleanup_free_ char *t = NULL;
+
+                        if (!j->rr)
+                                continue;
+
+                        if (!dns_key_is_shared(j->rr->key))
+                                continue;
+
+                        r = dns_packet_append_rr(p, j->rr, NULL, NULL);
+                        if (r < 0)
+                                return r;
+
+                        ancount ++;
+                }
+        }
+
+        DNS_PACKET_HEADER(p)->ancount = htobe16(ancount);
+
+        return 0;
+}
+
 void dns_cache_dump(DnsCache *cache, FILE *f) {
         Iterator iterator;
         DnsCacheItem *i;
diff --git a/src/resolve/resolved-dns-cache.h b/src/resolve/resolved-dns-cache.h
index 5f91164785..0f28bbe543 100644
--- a/src/resolve/resolved-dns-cache.h
+++ b/src/resolve/resolved-dns-cache.h
@@ -32,6 +32,7 @@ typedef struct DnsCache {
 } DnsCache;
 
 #include "resolved-dns-answer.h"
+#include "resolved-dns-packet.h"
 #include "resolved-dns-question.h"
 #include "resolved-dns-rr.h"
 
@@ -45,3 +46,5 @@ int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_
 
 void dns_cache_dump(DnsCache *cache, FILE *f);
 bool dns_cache_is_empty(DnsCache *cache);
+
+int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p);
diff --git a/src/resolve/resolved-dns-rr.h b/src/resolve/resolved-dns-rr.h
index 5cbb927681..5c2306ba96 100644
--- a/src/resolve/resolved-dns-rr.h
+++ b/src/resolve/resolved-dns-rr.h
@@ -250,6 +250,10 @@ int dns_resource_key_match_cname(const DnsResourceKey *key, const DnsResourceRec
 int dns_resource_key_to_string(const DnsResourceKey *key, char **ret);
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsResourceKey*, dns_resource_key_unref);
 
+static inline bool dns_key_is_shared(const DnsResourceKey *key) {
+        return IN_SET(key->type, DNS_TYPE_PTR);
+}
+
 DnsResourceRecord* dns_resource_record_new(DnsResourceKey *key);
 DnsResourceRecord* dns_resource_record_new_full(uint16_t class, uint16_t type, const char *name);
 DnsResourceRecord* dns_resource_record_ref(DnsResourceRecord *rr);
diff --git a/src/resolve/resolved-dns-transaction.c b/src/resolve/resolved-dns-transaction.c
index dccb8000a2..90f07e6c4b 100644
--- a/src/resolve/resolved-dns-transaction.c
+++ b/src/resolve/resolved-dns-transaction.c
@@ -24,6 +24,7 @@
 #include "dns-domain.h"
 #include "fd-util.h"
 #include "random-util.h"
+#include "resolved-dns-cache.h"
 #include "resolved-dns-transaction.h"
 #include "resolved-llmnr.h"
 #include "string-table.h"
@@ -733,6 +734,7 @@ static int dns_transaction_prepare_next_attempt(DnsTransaction *t, usec_t ts) {
 static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
 
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        bool add_known_answers = false;
         DnsTransaction *other;
         unsigned qdcount;
         usec_t ts;
@@ -754,6 +756,9 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
 
         qdcount = 1;
 
+        if (dns_key_is_shared(t->key))
+                add_known_answers = true;
+
         /*
          * For mDNS, we want to coalesce as many open queries in pending transactions into one single
          * query packet on the wire as possible. To achieve that, we iterate through all pending transactions
@@ -808,11 +813,21 @@ static int dns_transaction_make_packet_mdns(DnsTransaction *t) {
                 other->next_attempt_after = ts;
 
                 qdcount ++;
+
+                if (dns_key_is_shared(other->key))
+                        add_known_answers = true;
         }
 
         DNS_PACKET_HEADER(p)->qdcount = htobe16(qdcount);
         DNS_PACKET_HEADER(p)->id = t->id;
 
+        /* Append known answer section if we're asking for any shared record */
+        if (add_known_answers) {
+                r = dns_cache_export_shared_to_packet(&t->scope->cache, p);
+                if (r < 0)
+                        return r;
+        }
+
         t->sent = p;
         p = NULL;