RHEL 6 glibc IPv6 DNS resolution bug
We ran into an unpleasant bug in a Red Hat Enterprise Linux 6 glibc update a couple of weeks ago. It since has made its way into CentOS 6 as well.
The problem manifested itself in our particular case with this error from the Postfix mailer:
Jun 29 01:55:23 sl37 kernel: smtp: segfault at 1 ip 00007ffc0e455596 sp 00007fff99948f60 error 6 in libresolv-2.12.so[7ffc0e449000+16000]
But it affects all DNS resolution on the host, not just for mail.
If you have any IPv6 resolvers at all listed in /etc/resolv.conf, all your DNS resolution is likely to be broken with this version of glibc:
To work around the problem, you can either:
- Use only IPv4 DNS resolvers (comment out the IPv6 resolvers for now)
- or downgrade to the previous version of glibc using yum downgrade
Red Hat is aware of the bug and you can track progress toward a resolution in Bugzilla bug #835090.
If you’re using IPv6, watch out for this! If not, you’re fine.