[Bug 1676476] [NEW] Unable to do nsswitch resolution on Avahi due to permissions issue

[Ken D'Ambrosio]

Public bug reported:

I set up Avahi on two 16.04 systems, but was unable to resolve between
them via ping; note, however, that avahi-resolve worked fine:

root at clients-1:~# avahi-resolve -n -4 kentest.local
kentest.local    192.168.243.16   # This is a good thing


These, not so much good:
root at clients-1:~# ping kentest.local
ping: unknown host kentest.local

My nsswitch.conf file was thus:
hosts:          files mdns4_minimal [NOTFOUND=return] dns

I did a strace on the ping, and saw this:
sun_path="/var/run/avahi-daemon/socket"}, 110) = -1 EACCES (Permission denied)

The socket's permissions were fine, so I looked at the directory the socket was in and saw:
root at clients-1:~# ls -ald /var/run/avahi-daemon/
drwx------ 2 avahi avahi 80 Mar 27 05:35 /var/run/avahi-daemon/

It seemed to me this should have been okay -- I mean, I was trying the
ping as root, and presumably user avahi would be servicing the request
if it wasn't user root.  But "Permission denied" is "permission denied,"
so I changed directory permissions and tried again:

root at clients-1:~# chmod 777 /var/run/avahi-daemon/
root at clients-1:~# ping kentest.local
PING kentest.local (192.168.243.16) 56(84) bytes of data.
64 bytes from 192.168.243.16: icmp_seq=1 ttl=64 time=1.31 ms
64 bytes from 192.168.243.16: icmp_seq=2 ttl=64 time=0.742 ms

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: avahi-daemon 0.6.32~rc+dfsg-1ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-66.87-generic 4.4.44
Uname: Linux 4.4.0-66-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
Date: Mon Mar 27 14:55:01 2017
Ec2AMI: ami-00000004
Ec2AMIManifest: FIXME
Ec2AvailabilityZone: nova
Ec2InstanceType: GB.small
Ec2Kernel: unavailable
Ec2Ramdisk: unavailable
ProcEnviron:
 TERM=xterm
 SHELL=/bin/bash
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 XDG_RUNTIME_DIR=<set>
SourcePackage: avahi
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: avahi (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug ec2-images xenial

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https://bugs.launchpad.net/bugs/1676476

Title:
  Unable to do nsswitch resolution on Avahi due to permissions issue

Status in avahi package in Ubuntu:
  New

Bug description:
  I set up Avahi on two 16.04 systems, but was unable to resolve between
  them via ping; note, however, that avahi-resolve worked fine:

  root at clients-1:~# avahi-resolve -n -4 kentest.local
  kentest.local    192.168.243.16   # This is a good thing

  
  These, not so much good:
  root at clients-1:~# ping kentest.local
  ping: unknown host kentest.local

  My nsswitch.conf file was thus:
  hosts:          files mdns4_minimal [NOTFOUND=return] dns

  I did a strace on the ping, and saw this:
  sun_path="/var/run/avahi-daemon/socket"}, 110) = -1 EACCES (Permission denied)

  The socket's permissions were fine, so I looked at the directory the socket was in and saw:
  root at clients-1:~# ls -ald /var/run/avahi-daemon/
  drwx------ 2 avahi avahi 80 Mar 27 05:35 /var/run/avahi-daemon/

  It seemed to me this should have been okay -- I mean, I was trying the
  ping as root, and presumably user avahi would be servicing the request
  if it wasn't user root.  But "Permission denied" is "permission
  denied," so I changed directory permissions and tried again:

  root at clients-1:~# chmod 777 /var/run/avahi-daemon/
  root at clients-1:~# ping kentest.local
  PING kentest.local (192.168.243.16) 56(84) bytes of data.
  64 bytes from 192.168.243.16: icmp_seq=1 ttl=64 time=1.31 ms
  64 bytes from 192.168.243.16: icmp_seq=2 ttl=64 time=0.742 ms

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: avahi-daemon 0.6.32~rc+dfsg-1ubuntu2
  ProcVersionSignature: Ubuntu 4.4.0-66.87-generic 4.4.44
  Uname: Linux 4.4.0-66-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.5
  Architecture: amd64
  Date: Mon Mar 27 14:55:01 2017
  Ec2AMI: ami-00000004
  Ec2AMIManifest: FIXME
  Ec2AvailabilityZone: nova
  Ec2InstanceType: GB.small
  Ec2Kernel: unavailable
  Ec2Ramdisk: unavailable
  ProcEnviron:
   TERM=xterm
   SHELL=/bin/bash
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   XDG_RUNTIME_DIR=<set>
  SourcePackage: avahi
  UpgradeStatus: No upgrade log present (probably fresh install)

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