dnssd.c: Enable service registration on loopback

In case users would like to prevent sharing services from printer applications to local network, restrict it to localhost and let CUPS do the sharing. This can be done by setting `listen-hostname` in PAPPL API - this prevents accessing the public addresses, but the service is still published on those public addresses. The PR does the following: - update system hostname internally in `papplAddListeners()` - dnssd functions will check system hostname and if it is localhost, it will use loopback index - in case of Avahi it passes NULL as hostname to let Avahi decide what hostname to use (in case of hostname conflicts) The result is that if system hostname is set to localhost internally, the service is published on `.local` address, but resolved to loopback because CUPS uses DNS-SD names in URIs.
michaelrsweet · Mar 19, 2024 · 3e88a44 · 3e88a44
1 parent 78d1ee4
commit 3e88a44
Show file tree

Hide file tree

Showing 4 changed files with 60 additions and 12 deletions.
diff --git a/pappl/dnssd-private.h b/pappl/dnssd-private.h
@@ -52,6 +52,7 @@ typedef void *_pappl_dns_sd_t;		// DNS-SD master reference
 extern const char	*_papplDNSSDCopyHostName(char *buffer, size_t bufsize) _PAPPL_PRIVATE;
 extern int		_papplDNSSDGetHostChanges(void) _PAPPL_PRIVATE;
 extern _pappl_dns_sd_t	_papplDNSSDInit(pappl_system_t *system) _PAPPL_PRIVATE;
+extern bool		_papplDNSSDIsLoopback(const char *name) _PAPPL_PRIVATE;
 extern void		_papplDNSSDLock(void) _PAPPL_PRIVATE;
 extern const char	*_papplDNSSDStrError(int error) _PAPPL_PRIVATE;
 extern void		_papplDNSSDUnlock(void) _PAPPL_PRIVATE;

diff --git a/pappl/dnssd.c b/pappl/dnssd.c
@@ -26,8 +26,13 @@
 
 static char		pappl_dns_sd_hostname[256] = "";
 					// Current DNS-SD hostname
+#ifdef HAVE_MDNSRESPONDER
 static int		pappl_dns_sd_hostname_changes = 0;
 					// Number of host name changes/collisions
+#elif defined(HAVE_AVAHI)
+static int		pappl_dns_sd_hostname_changes = -1;
+					// Number of host name changes/collisions
+#endif // HAVE_MDNSRESPONDER
 static pthread_mutex_t	pappl_dns_sd_hostname_mutex = PTHREAD_MUTEX_INITIALIZER;
 					// Host name mutex
 #ifdef HAVE_MDNSRESPONDER
@@ -386,15 +391,15 @@ _papplPrinterRegisterDNSSDNoLock(
   _pappl_dns_sd_t	master;		// DNS-SD master reference
 
 
-  if (!printer->dns_sd_name || !printer->system->is_running)
+  if (!printer->dns_sd_name || !printer->system->is_running || !system->hostname)
     return (false);
 
   papplLogPrinter(printer, PAPPL_LOGLEVEL_DEBUG, "Registering DNS-SD name '%s' on '%s'", printer->dns_sd_name, printer->system->hostname);
 
 #  ifdef HAVE_MDNSRESPONDER
-  if_index = !strcmp(system->hostname, "localhost") ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
+  if_index = _papplDNSSDIsLoopback(system->hostname) ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
 #  else
-  if_index = !strcmp(system->hostname, "localhost") ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
+  if_index = _papplDNSSDIsLoopback(system->hostname) ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
 #  endif // HAVE_MDNSRESPONDER
 
   // Get attributes and values for the TXT record...
@@ -741,7 +746,7 @@ _papplPrinterRegisterDNSSDNoLock(
   }
 
   // Then register the IPP/IPPS services...
-  if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_ipp._tcp", NULL, system->hostname, system->port, txt)) < 0)
+  if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_ipp._tcp", NULL, NULL, system->port, txt)) < 0)
   {
     papplLogPrinter(printer, PAPPL_LOGLEVEL_ERROR, "Unable to register '%s._ipp._tcp': %s", printer->dns_sd_name, _papplDNSSDStrError(error));
     ret = false;
@@ -772,7 +777,7 @@ _papplPrinterRegisterDNSSDNoLock(
 
   if (!(printer->system->options & PAPPL_SOPTIONS_NO_TLS))
   {
-    if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_ipps._tcp", NULL, system->hostname, system->port, txt)) < 0)
+    if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_ipps._tcp", NULL, NULL, system->port, txt)) < 0)
     {
       papplLogPrinter(printer, PAPPL_LOGLEVEL_ERROR, "Unable to register '%s._ipps._tcp': %s", printer->dns_sd_name, _papplDNSSDStrError(error));
       ret = false;
@@ -827,7 +832,7 @@ _papplPrinterRegisterDNSSDNoLock(
     txt = avahi_string_list_add_printf(txt, "PaperMax=%s", papermax);
     txt = avahi_string_list_add_printf(txt, "Scan=F");
 
-    if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_pdl-datastream._tcp", NULL, system->hostname, 9099 + printer->printer_id, txt)) < 0)
+    if ((error = avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_pdl-datastream._tcp", NULL, NULL, 9099 + printer->printer_id, txt)) < 0)
     {
       papplLogPrinter(printer, PAPPL_LOGLEVEL_ERROR, "Unable to register '%s._pdl-datastream._tcp': %s", printer->dns_sd_name, _papplDNSSDStrError(error));
       ret = false;
@@ -860,7 +865,7 @@ _papplPrinterRegisterDNSSDNoLock(
   txt = NULL;
   txt = avahi_string_list_add_printf(txt, "path=%s/", printer->uriname);
 
-  avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_http._tcp", NULL, system->hostname, system->port, txt);
+  avahi_entry_group_add_service_strlst(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_http._tcp", NULL, NULL, system->port, txt);
   avahi_entry_group_add_service_subtype(printer->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, printer->dns_sd_name, "_http._tcp", NULL, "_printer._sub._http._tcp");
 
   avahi_string_list_free(txt);
@@ -951,9 +956,9 @@ _papplSystemRegisterDNSSDNoLock(
   papplLog(system, PAPPL_LOGLEVEL_DEBUG, "Registering DNS-SD name '%s' on '%s'", system->dns_sd_name, system->hostname);
 
 #  ifdef HAVE_MDNSRESPONDER
-  if_index = !strcmp(system->hostname, "localhost") ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
+  if_index = _papplDNSSDIsLoopback(system->hostname) ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
 #  else
-  if_index = !strcmp(system->hostname, "localhost") ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
+  if_index = _papplDNSSDIsLoopback(system->hostname) ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
 #  endif // HAVE_MDNSRESPONDER
 
   if (system->geo_location)
@@ -1080,7 +1085,7 @@ _papplSystemRegisterDNSSDNoLock(
 
   if (!(system->options & PAPPL_SOPTIONS_NO_TLS))
   {
-    if ((error = avahi_entry_group_add_service_strlst(system->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, system->dns_sd_name, "_ipps-system._tcp", NULL, system->hostname, system->port, txt)) < 0)
+    if ((error = avahi_entry_group_add_service_strlst(system->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, system->dns_sd_name, "_ipps-system._tcp", NULL, NULL, system->port, txt)) < 0)
     {
       papplLog(system, PAPPL_LOGLEVEL_ERROR, "Unable to register '%s._ipps-system._tcp': %s", system->dns_sd_name, _papplDNSSDStrError(error));
       ret = false;
@@ -1104,7 +1109,7 @@ _papplSystemRegisterDNSSDNoLock(
   // Finally _http.tcp (HTTP) for the web interface...
   if (system->options & PAPPL_SOPTIONS_MULTI_QUEUE)
   {
-    avahi_entry_group_add_service_strlst(system->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, system->dns_sd_name, "_http._tcp", NULL, system->hostname, system->port, NULL);
+    avahi_entry_group_add_service_strlst(system->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, system->dns_sd_name, "_http._tcp", NULL, NULL, system->port, NULL);
     avahi_entry_group_add_service_subtype(system->dns_sd_ref, if_index, AVAHI_PROTO_UNSPEC, 0, system->dns_sd_name, "_http._tcp", NULL, "_printer._sub._http._tcp");
   }
 
@@ -1475,3 +1480,25 @@ dns_sd_system_callback(
   }
 }
 #endif // HAVE_MDNSRESPONDER
+
+
+//
+// '_papplDNSSDIsLoopback()' - Find out whether the string means
+//                           localhost
+//
+
+bool
+_papplDNSSDIsLoopback(const char *name)
+{
+  if (!name)
+    return (false);
+
+  if (!strcasecmp(name, "localhost"))
+    return (true);
+  else if (!strcmp(name, "127.0.0.1"))
+    return (true);
+  else if (!strcmp(name, "[::1]"))
+    return (true);
+
+  return (false);
+}
diff --git a/pappl/system-accessors.c b/pappl/system-accessors.c
@@ -100,6 +100,13 @@ papplSystemAddListeners(
       if (ret)
         system->port = port;
     }
+
+    if (system->hostname)
+    {
+      free(system->hostname);
+    }
+
+    system->hostname = strdup(name);
   }
   else if (name && *name == '[')
   {
@@ -128,6 +135,11 @@ papplSystemAddListeners(
       if (ret)
         system->port = port;
     }
+
+    if (system->hostname)
+      free(system->hostname);
+
+    system->hostname = strdup(name);
   }
   else
   {
@@ -160,6 +172,14 @@ papplSystemAddListeners(
         add_listeners(system, name, port, AF_INET6);
       }
     }
+
+    if (name && !strcasecmp(name, "localhost"))
+    {
+      if (system->hostname)
+        free(system->hostname);
+
+      system->hostname = strdup(name);
+    }
   }
 
   return (ret);

diff --git a/pappl/system.c b/pappl/system.c
@@ -652,7 +652,7 @@ papplSystemRun(pappl_system_t *system)	// I - System
       bool		force_dns_sd = system->dns_sd_host_changes != dns_sd_host_changes;
 					// Force re-registration?
 
-      if (force_dns_sd)
+      if (!_papplDNSSDIsLoopback(system->hostname) && force_dns_sd)
         _papplSystemSetHostNameNoLock(system, NULL);
 
       if (system->dns_sd_collision || force_dns_sd)