Public bug reported:
[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.
** Affects: keyutils (Ubuntu)
Importance: Undecided
Assignee: Utkarsh Gupta (utkarsh)
Status: In Progress
** Affects: keyutils (Ubuntu Focal)
Importance: Undecided
Status: New
** Affects: keyutils (Ubuntu Impish)
Importance: Undecided
Status: New
** Also affects: keyutils (Ubuntu Impish)
Importance: Undecided
Status: New
** Also affects: keyutils (Ubuntu Focal)
Importance: Undecided
Status: New
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1962453
Title:
Apply default TTL to records obtained from getaddrinfo()
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/keyutils/+bug/1962453/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
