Thanks for your insight Alex. I've managed to reproduce this now, with the following steps:
On Lucid:
1. sudo apt-get install bind9
2. sudo apt-get remove bind9
# this removes /var/cache/bind but leaves /etc/bind9/rndc.key
3. sudo apt-get install bind9
# Now the postinst doesn't fix /var/cache/bind, but on Lucid nobody will notice this problem
4. sudo do-release-upgrade
# bind now uses /var/cache/bind/managed-keys.bind and the problem occurs
After the upgrade to Precise, bind9 is in the situation you described (permissions on /var/cache/bind wrong), with 100% CPU consumption.
I couldn't reproduce the problem directly on Precise because on package removal /var/cache/bind/managed-keys.bind is left behind and so /var/cache/bind never gets removed (I think this is a separate bug in itself).
It seems likely to me that this issue will affect Debian also, so next I will test this and file a bug report in Debian as needed, so that we can coordinate a fix.
Thanks for your insight Alex. I've managed to reproduce this now, with the following steps:
On Lucid: bind/managed- keys.bind and the problem occurs
1. sudo apt-get install bind9
2. sudo apt-get remove bind9
# this removes /var/cache/bind but leaves /etc/bind9/rndc.key
3. sudo apt-get install bind9
# Now the postinst doesn't fix /var/cache/bind, but on Lucid nobody will notice this problem
4. sudo do-release-upgrade
# bind now uses /var/cache/
After the upgrade to Precise, bind9 is in the situation you described (permissions on /var/cache/bind wrong), with 100% CPU consumption.
I couldn't reproduce the problem directly on Precise because on package removal /var/cache/ bind/managed- keys.bind is left behind and so /var/cache/bind never gets removed (I think this is a separate bug in itself).
It seems likely to me that this issue will affect Debian also, so next I will test this and file a bug report in Debian as needed, so that we can coordinate a fix.