[Pkg-libvirt-maintainers] Bug#923249: libvirt0: libvirt sets disable_ipv6 on bridge, entirely breaking internal IPv6 networking

[Ralf Jung]

Package: libvirt0
Version: 5.0.0-1
Severity: grave
Justification: renders package unusable

Dear Maintainer,

After a recent upgrade, IPv6 communication between a virtual router and another
virtual client over an isolated network stopped working. I am seeing the rotuer
advertisments sent by the router on vnet0, which is attached to the bridge
virbr1, but when I capture packages on the bridge, the IPv6 traffic is gone.  It
just took me several hours of debugging to realize that the reason for this is
that /proc/sys/net/ipv6/conf/virbr1/disable_ipv6 is set to 1.  After setting it
to 0, IPv6 is working as expected now.

This is a regression, IPv6 used to work between virtual clients just fine
without having to manually fiddle with the network configuration.

Kind regards,
Ralf

-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable-debug'), (500, 'testing-debug'), (100, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.19.0-2-amd64 (SMP w/8 CPU cores)
Kernel taint flags: TAINT_USER, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages libvirt0 depends on:
ii  libacl1             2.2.52-3+b1
ii  libapparmor1        2.13.2-7
ii  libaudit1           1:2.8.4-2
ii  libavahi-client3    0.7-4+b1
ii  libavahi-common3    0.7-4+b1
ii  libc6               2.28-7
ii  libcap-ng0          0.7.9-2
ii  libcurl3-gnutls     7.64.0-1
ii  libdbus-1-3         1.12.12-1
ii  libdevmapper1.02.1  2:1.02.155-2
ii  libgcc1             1:8.2.0-21
ii  libgnutls30         3.6.6-2
ii  libnl-3-200         3.4.0-1
ii  libnl-route-3-200   3.4.0-1
ii  libnuma1            2.0.12-1
ii  libsasl2-2          2.1.27+dfsg-1
ii  libselinux1         2.8-1+b1
ii  libssh2-1           1.8.0-2
ii  libxml2             2.9.4+dfsg1-7+b3
ii  libyajl2            2.1.0-3

Versions of packages libvirt0 recommends:
ii  lvm2  2.03.02-2

libvirt0 suggests no packages.

-- no debconf information