ufw does not support rule removal. For a particular project (a task queue on a
cloud adhoc HPC cluster), I have had the occasion to test it in a relatively
massive parallel rate (20 concurrent uses). I have experienced:
- nice behaviour when adding rules,
- bad behaviour when removing rules.
I was triggering ufw with ansible parallel playbooks execution.
When removing rules the defect rate was high (as soon as more than two
playbooks were launched together, some of the rules were not deleted).
In that case, ufw fails silently, which is quite bad.
As a counter measure I used task-spooler (apt install task-spooler) I changed
my ansible task from:
```yaml
community.general.ufw:
from_ip: "{{ hostvars[nodename].ipv4 }}"
rule: allow
delete: yes
```
to
```yaml
ansible.builtin.script:
cmd: /usr/bin/tsp /usr/sbin/ufw delete allow from "{{
hostvars[nodename].ipv4 }}"
become: true
```
This solved the issue.
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https://bugs.launchpad.net/bugs/1204579
Title:
ufw doesn't support concurrent updates
Status in ufw:
Fix Released
Status in ufw package in Ubuntu:
Fix Released
Status in ufw source package in Bionic:
Fix Released
Status in ufw source package in Cosmic:
Fix Released
Status in ufw source package in Disco:
Fix Released
Status in ufw package in Debian:
Fix Released
Bug description:
[Impact]
ufw prior to 0.36 did not support locking or use xtables locking which
can lead to problems when using ufw as a dynamic firewall.
[Test Case]
$ sudo apt-get install python-minimal # for the test script
$ sudo ./test_ufw_threads.py # this runs for many seconds
A patched ufw will complete with no errors. With an unpatched ufw, there will
be many errors like:
$ sudo ./test_ufw_threads.py
...
ERROR: initcaps
[Errno 2] iptables: Chain already exists.
ERROR: initcaps
[Errno 2] iptables: Chain already exists.
[Regression Potential]
ufw 0.36 implements a global exclusive lock before doing any kernel or
file writes. Risk of regression includes the lock file not being
released due to coding error. The locking is done via fcntl.lockf and
ufw releases it in a finally clause that is careful to always release
it.
[Other Info]
This locking code has been in production in the ufw snap for years and
is known to work is static environments as well as in dynamic
environments (IPS/fail2ban/etc).
= Original description =
On a server under Ubuntu 12.04 I automatically update firewall rules and I
unfortunately noticed that if 2 rules are processed at the same time it leads
to an inconsistent result between iptables and ufw status.
In fact it can be reproduced using the python script in attachment.
Before executing this script I didn't have any rules matching the ip
192.168.254.1 on my computer.
After a launch iptables takes into acount 464 rules.
sudo iptables -L -n | grep 192.168.254.1 | wc -l
464
It should be 500 rules but the script stressed a lot my system and all rules
can't be processed by iptables
sudo ./test_ufw_threads.py
iptables: Resource temporarily unavailable.
iptables: Resource temporarily unavailable.
iptables: Resource temporarily unavailable.
[...]
Anyway, ufw stores only the last updates (in /lib/ufw/user.rules):
sudo ufw status
État : actif
Vers Action Depuis
---- ------ ------
192.168.254.1 1234/tcp ALLOW 192.168.46.9
192.168.254.1 1234/tcp ALLOW 192.168.22.10
192.168.254.1 1234/tcp ALLOW 192.168.32.10
192.168.254.1 1234/tcp ALLOW 192.168.5.10
192.168.254.1 1234/tcp ALLOW 192.168.43.9
192.168.254.1 1234/tcp ALLOW 192.168.40.10
192.168.254.1 1234/tcp ALLOW 192.168.46.10
192.168.254.1 1234/tcp ALLOW 192.168.48.10
192.168.254.1 1234/tcp ALLOW 192.168.42.10
192.168.254.1 1234/tcp ALLOW 192.168.43.10
So I can't delete other rules using ufw, I had to directly use iptables.
In this case I can only delete 10 rules using ufw.
Could you please handle some kind of lock?
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