This bug was fixed in the package keyutils - 1.5.9-9.2ubuntu2.1
---------------
keyutils (1.5.9-9.2ubuntu2.1) bionic; urgency=medium
* d/p/apply-default-ttl-to-records.patch: Add patch
to apply default TTL to records obtained from
getaddrinfo(). (LP: #1962453)
-- Utkarsh Gupta <utka...@ubuntu.com> Tue, 08 Mar 2022 13:26:12 +0530
** Changed in: keyutils (Ubuntu Bionic)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1962453
Title:
Apply default TTL to records obtained from getaddrinfo()
Status in keyutils package in Ubuntu:
Fix Released
Status in keyutils source package in Bionic:
Fix Released
Status in keyutils source package in Focal:
Incomplete
Status in keyutils source package in Impish:
Incomplete
Bug description:
[Impact]
========
There's a strong dependency for cifs.ko (and nfs.ko) on keyutils for
DNS resolution. The keyutils package contains the userspace utility to
update the kernel keyring with the DNS mapping to IP address. Prior to
1.6.2, this utility may erroneously set unlimited lifetime for this
keyring in the kernel.
[Test plan]
===========
1. Create a file share on an SMB server (can be a samba server) with
two IP addresses. Make sure that FQDN of the server resolves to one of
these addresses.
2. mount the created share on the cifs client using the FQDN for the
server. Make sure that the mount point is accessible.
3. Using the ss command on the client, to kill the sockets that
connect to the server: sudo ss -K dport :445
4. Now update the DNS entry to make sure that the server FQDN now
resolves to the second IP address of the server. Make sure that
nslookup on the client now resolves to the new IP address.
5. Repeat step 3 to kill the sockets that connect to server to force
re-connection again.
Without the fix, after step 5, with the "ss -t" command, you'll see
that the client has reconnected to the old IP address, even when DNS
lookups return the new IP.
With the fix (after a reboot of the client machine to make sure that
kernel keys are refreshed), you'll see that the client reconnects to
the new IP address.
The bug is due to unlimited lifetime set by key.dns_resolver (which is
part of keyutils package). As a result, even if IP address for the DNS
entries change, the kernel filesystems would continue to use old IP
address, due to the cached keys. This issue causes clients to
misbehave when Azure Files service endpoints move to a different
cluster.
[Where problems could occur]
============================
Address records obtained from getaddrinfo() don't come with any TTL
information, even if they're obtained from the DNS, so if someone is
relying on this particularly, might face some problem/regression but I
don't think they would face that as it would still be highly
configurable.
[Other information]
===================
This request is essentially from one of our cloud partners and they're
highly affected by this.
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