[Bug 2002891] Re: avahi_service_browser_new() failed: Invalid service type

[Seth Arnold]

Hello Hadmut, my first inclination is that this isn't a security issue:

- services should use cryptographic verification of both peers, if this is important
- network administrators can use port security settings on their equipment to restrict which hosts can communicate in which fashions

If I've overlooked something, please do let us know.

Thanks

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Title:
  avahi_service_browser_new() failed: Invalid service type

Status in avahi package in Ubuntu:
  New

Bug description:
  Hi,

  on a network, where the router offers DHCP, but does not put the DHCP
  clients in a DNS domain, thus where it is necessary to use mdns/avahi
  instead, I ran into several problems with avahi.

  One is
  avahi-browse -a -t     
  avahi_service_browser_new() failed: Invalid service type

  No other output. i.e. it just does not work.

  In this network, all Ubuntu machines show this behaviour.

  In my other network (with working DHCP-DNS, different router,
  different brand, therefore not depending on mdns) the problem does not
  occur

  Since the debugging output of avahi software is – if at all – very
  poor, I cannot see what causes this problem. However, dbus-monitor
  --system showed

  ...

  method call time=1673742811.321042 sender=:1.692 -> destination=org.freedesktop.Avahi serial=10 path=/; interface=org.freedesktop.Avahi.Server; member=ServiceBrowserNew
     int32 -1
     int32 -1
     string "_ipp._tcp"
     string "local"
     uint32 0
  method return time=1673742811.321093 sender=:1.479 -> destination=:1.692 serial=557 reply_serial=10
     object path "/Client29/ServiceBrowser3"
  method call time=1673742811.321259 sender=:1.692 -> destination=org.freedesktop.Avahi serial=11 path=/; interface=org.freedesktop.Avahi.Server; member=ServiceBrowserNew
     int32 -1
     int32 -1
     string "_scanner._tcp"
     string "local"
     uint32 0
  method return time=1673742811.321301 sender=:1.479 -> destination=:1.692 serial=558 reply_serial=11
     object path "/Client29/ServiceBrowser4"
  method call time=1673742811.321391 sender=:1.692 -> destination=org.freedesktop.Avahi serial=12 path=/; interface=org.freedesktop.Avahi.Server; member=ServiceBrowserNew
     int32 -1
     int32 -1
     string ""
     string ""
     uint32 0
  error time=1673742811.321479 sender=:1.479 -> destination=:1.692 error_name=org.freedesktop.Avahi.InvalidServiceTypeError reply_serial=12
     string "Invalid service type"

  
  So it seems as if the client (browser) queries one services after the other, which works, but then an empty string as a name, which is rejected by the daemon, which then makes the client to spit out this error message and then terminate immediately. 

  Since I have similar (i.e. very similar, both created with puppet)
  machines, and all machines in one network fail, while similar machines
  in another don't, I guess that the problem is caused by some network
  reply, maybe a printer.

  
  This, however, could be a security problem, because if someone can cause avahi and thus mdns resolution to fail in networks like this here, where the router and dhcp server does not offer the host names in a DNS domain (Huawei glass fiber router), a malformed packet could cause the mdns resolution of avahi to fail and therefore could be used for an attack, effectively blocking certain kinds of mdns service resolution. But since I have not yet understood what really causes this problem, it is just an assumption. 

  regards

  ProblemType: Bug
  DistroRelease: Ubuntu 22.04
  Package: avahi-utils 0.8-5ubuntu5
  ProcVersionSignature: Ubuntu 5.15.0-58.64-generic 5.15.74
  Uname: Linux 5.15.0-58-generic x86_64
  NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
  ApportVersion: 2.20.11-0ubuntu82.3
  Architecture: amd64
  CasperMD5CheckResult: pass
  CurrentDesktop: XFCE
  Date: Sun Jan 15 02:35:24 2023
  InstallationDate: Installed on 2022-12-25 (20 days ago)
  InstallationMedia: Xubuntu 22.04.1 LTS "Jammy Jellyfish" - Release amd64 (20220809.1)
  SourcePackage: avahi
  UpgradeStatus: No upgrade log present (probably fresh install)

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