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dnssd.c: Enable service registration on loopback
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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.
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@zdohnal
zdohnal committed Mar 14, 2024
1 parent cf6c821 commit 0ac1c0d
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Showing 2 changed files with 51 additions and 11 deletions.
42 changes: 31 additions & 11 deletions pappl/dnssd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@ static AvahiThreadedPoll *pappl_dns_sd_poll = NULL;
//

static void dns_sd_geo_to_loc(const char *geo, unsigned char loc[16]);
static bool dns_sd_is_loopback(const char *name);
#ifdef HAVE_MDNSRESPONDER
static void DNSSD_API dns_sd_hostname_callback(DNSServiceRef ref, DNSServiceFlags flags, uint32_t if_index, DNSServiceErrorType error, const char *fullname, uint16_t rrtype, uint16_t rrclass, uint16_t rdlen, const void *rdata, uint32_t ttl, void *context);
static void DNSSD_API dns_sd_printer_callback(DNSServiceRef sdRef, DNSServiceFlags flags, DNSServiceErrorType errorCode, const char *name, const char *regtype, const char *domain, pappl_printer_t *printer);
Expand Down Expand Up @@ -386,15 +387,15 @@ _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 = dns_sd_is_loopback(system->hostname) ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
# else
if_index = !strcmp(system->hostname, "localhost") ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
if_index = dns_sd_is_loopback(system->hostname) ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
# endif // HAVE_MDNSRESPONDER

// Get attributes and values for the TXT record...
Expand Down Expand Up @@ -741,7 +742,7 @@ _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;
Expand Down Expand Up @@ -772,7 +773,7 @@ _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;
Expand Down Expand Up @@ -827,7 +828,7 @@ _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;
Expand Down Expand Up @@ -860,7 +861,7 @@ _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);
Expand Down Expand Up @@ -951,9 +952,9 @@ _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 = dns_sd_is_loopback(system->hostname) ? kDNSServiceInterfaceIndexLocalOnly : kDNSServiceInterfaceIndexAny;
# else
if_index = !strcmp(system->hostname, "localhost") ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
if_index = dns_sd_is_loopback(system->hostname) ? if_nametoindex("lo") : AVAHI_IF_UNSPEC;
# endif // HAVE_MDNSRESPONDER

if (system->geo_location)
Expand Down Expand Up @@ -1080,7 +1081,7 @@ _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;
Expand All @@ -1104,7 +1105,7 @@ _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");
}

Expand Down Expand Up @@ -1475,3 +1476,22 @@ dns_sd_system_callback(
}
}
#endif // HAVE_MDNSRESPONDER


//
// 'dns_sd_is_loopback()' - Find out whether the string means
// localhost
//

static bool
dns_sd_is_loopback(const char *name)
{
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);
}
20 changes: 20 additions & 0 deletions pappl/system-accessors.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,13 @@ papplSystemAddListeners(
if (ret)
system->port = port;
}

if (system->hostname)
{
free(system->hostname);
}

system->hostname = strdup(name);
}
else if (name && *name == '[')
{
Expand Down Expand Up @@ -128,6 +135,11 @@ papplSystemAddListeners(
if (ret)
system->port = port;
}

if (system->hostname)
free(system->hostname);

system->hostname = strdup(name);
}
else
{
Expand Down Expand Up @@ -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);
Expand Down

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