From: Ronan Pigott <ronan@rjp.ie>
Date: Tue, 19 Mar 2024 08:56:03 +0000 (-0700)
Subject: dnssd: don't advertise subtype PTRs to the browsing domain
X-Git-Tag: v256-rc1~472
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cd40efc671e9bfbefb70e409afc2fab62948ae1f;p=thirdparty%2Fsystemd.git

dnssd: don't advertise subtype PTRs to the browsing domain

The RFC6763 § 9 recommendation is to advertise only the two-label
service names.

Fixes: 88123aa21c26 ("dnssd: support service subtypes")
---

diff --git a/src/resolve/resolved-dns-rr.c b/src/resolve/resolved-dns-rr.c
index ca30508ff4c..2739bed41a3 100644
--- a/src/resolve/resolved-dns-rr.c
+++ b/src/resolve/resolved-dns-rr.c
@@ -182,6 +182,23 @@ bool dns_resource_key_is_dnssd_ptr(const DnsResourceKey *key) {
                 dns_name_endswith(dns_resource_key_name(key), "_udp.local");
 }
 
+bool dns_resource_key_is_dnssd_two_label_ptr(const DnsResourceKey *key) {
+        assert(key);
+
+        /* Check if this is a PTR resource key used in Service Instance
+         * Enumeration as described in RFC6763 § 4.1, excluding selective
+         * service names described in RFC6763 § 7.1. */
+
+        if (key->type != DNS_TYPE_PTR)
+                return false;
+
+        const char *name = dns_resource_key_name(key);
+        if (dns_name_parent(&name) <= 0)
+                return false;
+
+        return dns_name_equal(name, "_tcp.local") || dns_name_equal(name, "_udp.local");
+}
+
 int dns_resource_key_equal(const DnsResourceKey *a, const DnsResourceKey *b) {
         int r;
 
diff --git a/src/resolve/resolved-dns-rr.h b/src/resolve/resolved-dns-rr.h
index 8ad4009ebf7..156fa018735 100644
--- a/src/resolve/resolved-dns-rr.h
+++ b/src/resolve/resolved-dns-rr.h
@@ -334,6 +334,7 @@ DnsResourceKey* dns_resource_key_unref(DnsResourceKey *key);
 const char* dns_resource_key_name(const DnsResourceKey *key);
 bool dns_resource_key_is_address(const DnsResourceKey *key);
 bool dns_resource_key_is_dnssd_ptr(const DnsResourceKey *key);
+bool dns_resource_key_is_dnssd_two_label_ptr(const DnsResourceKey *key);
 int dns_resource_key_equal(const DnsResourceKey *a, const DnsResourceKey *b);
 int dns_resource_key_match_rr(const DnsResourceKey *key, DnsResourceRecord *rr, const char *search_domain);
 int dns_resource_key_match_cname_or_dname(const DnsResourceKey *key, const DnsResourceKey *cname, const char *search_domain);
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index b1ae36e3909..17bc8231962 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -1504,9 +1504,10 @@ int dns_scope_announce(DnsScope *scope, bool goodbye) {
                         continue;
                 }
 
-                /* Collect service types for _services._dns-sd._udp.local RRs in a set */
+                /* Collect service types for _services._dns-sd._udp.local RRs in a set. Only two-label names
+                 * (not selective names) are considered according to RFC6763 § 9. */
                 if (!scope->announced &&
-                    dns_resource_key_is_dnssd_ptr(z->rr->key)) {
+                    dns_resource_key_is_dnssd_two_label_ptr(z->rr->key)) {
                         if (!set_contains(types, dns_resource_key_name(z->rr->key))) {
                                 r = set_ensure_put(&types, &dns_name_hash_ops, dns_resource_key_name(z->rr->key));
                                 if (r < 0)