avahi_client_free() called with NULL pointer during shutdown

[michaelrsweet]

Version: 2.0.1
CUPS.org User: foutrelis

During system shutdown, CUPS logs the following error:

Unable to communicate with avahi-daemon: An unexpected D-Bus error occured

Shortly after that, cupsd calls avahi_client_free() with a NULL DNSSDClient pointer and immediately terminates with SIGABRT.

According to the systemd journal, "Avahi mDNS/DNS-SD Stack" is stopped before "CUPS Scheduler". My guess is that DNSSDClient is freed and set to NULL by dnssdClientCallback() following the termination of the Avahi daemon.

A simple solution would be to check if DNSSDClient is NULL before calling avahi_client_free() in dnssdStop(). Either a (DNSSDClient != NULL) or (avahi_running == 1) condition should suffice.

I'm using Arch Linux on x86_64 with the following software:

• cups 2.0.1
• systemd 218
• avahi 0.6.31

[michaelrsweet]

CUPS.org User: mike

Fixed in Subversion repository.

[michaelrsweet]

"str4550.patch":

Index: scheduler/dirsvc.c

--- scheduler/dirsvc.c (revision 12451)
+++ scheduler/dirsvc.c (working copy)
@@ -3,7 +3,7 @@
*

• Directory services routines for the CUPS scheduler.
  *

  • * Copyright 2007-2014 by Apple Inc.
  • * Copyright 2007-2015 by Apple Inc.

• Copyright 1997-2007 by Easy Software Products, all rights reserved.
  *

• These coded instructions, statements, and computer programs are the
  @@ -1296,13 +1296,20 @@
  DNSSDMaster = NULL;

  else /* HAVE_AVAHI */

  • avahi_threaded_poll_stop(DNSSDMaster);
  • if (DNSSDMaster)
  • avahi_threaded_poll_stop(DNSSDMaster);

• avahi_client_free(DNSSDClient);

• DNSSDClient = NULL;

• if (DNSSDClient)

• {

• avahi_client_free(DNSSDClient);

• DNSSDClient = NULL;

• }

• avahi_threaded_poll_free(DNSSDMaster);

• DNSSDMaster = NULL;

• if (DNSSDMaster)

• {

• avahi_threaded_poll_free(DNSSDMaster);

• DNSSDMaster = NULL;

• }

endif /* HAVE_DNSSD */

cupsArrayDelete(DNSSDPrinters);