Will Ansible prevent the execution of 'rm -rf /' in a shell script
Solution 1:
I have virtual machines, let's blow a bunch of them up! For science.
[root@diaf ~]# ansible --version
ansible 2.0.1.0
config file = /etc/ansible/ansible.cfg
configured module search path = Default w/o overrides
First attempt:
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
command: "rm -rf {x}/{y}"
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
ESTABLISH LOCAL CONNECTION FOR USER: root
localhost EXEC /bin/sh -c '( umask 22 && mkdir -p "` echo $HOME/.ansible/tmp/ansible-tmp-1461128819.56-86533871334374 `" && echo "` echo $HOME/.ansible/tmp/ansible-tmp-1461128819.56-86533871334374 `" )'
localhost PUT /tmp/tmprogfhZ TO /root/.ansible/tmp/ansible-tmp-1461128819.56-86533871334374/command
localhost EXEC /bin/sh -c 'LANG=en_US.UTF-8 LC_ALL=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 /usr/bin/python /root/.ansible/tmp/ansible-tmp-1461128819.56-86533871334374/command; rm -rf "/root/.ansible/tmp/ansible-tmp-1461128819.56-86533871334374/" > /dev/null 2>&1'
changed: [localhost] => {"changed": true, "cmd": ["rm", "-rf", "{x}/{y}"], "delta": "0:00:00.001844", "end": "2016-04-20 05:06:59.601868", "invocation": {"module_args": {"_raw_params": "rm -rf {x}/{y}", "_uses_shell": false, "chdir": null, "creates": null, "executable": null, "removes": null, "warn": true}, "module_name": "command"}, "rc": 0, "start": "2016-04-20 05:06:59.600024", "stderr": "", "stdout": "", "stdout_lines": [], "warnings": ["Consider using file module with state=absent rather than running rm"]}
[WARNING]: Consider using file module with state=absent rather than running rm
PLAY RECAP *********************************************************************
localhost : ok=1 changed=1 unreachable=0 failed=0
OK, so command just passes the literals along, and nothing happens.
How about our favorite safety bypass, raw?
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
raw: "rm -rf {x}/{y}"
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
ESTABLISH LOCAL CONNECTION FOR USER: root
localhost EXEC rm -rf {x}/{y}
ok: [localhost] => {"changed": false, "invocation": {"module_args": {"_raw_params": "rm -rf {x}/{y}"}, "module_name": "raw"}, "rc": 0, "stderr": "", "stdout": "", "stdout_lines": []}
PLAY RECAP *********************************************************************
localhost : ok=1 changed=0 unreachable=0 failed=0
No go again! How hard can it possibly be to delete all your files?
Oh, but what if they were undefined variables or something?
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
command: "rm -rf {{x}}/{{y}}"
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
fatal: [localhost]: FAILED! => {"failed": true, "msg": "'x' is undefined"}
NO MORE HOSTS LEFT *************************************************************
to retry, use: --limit @killme.retry
PLAY RECAP *********************************************************************
localhost : ok=0 changed=0 unreachable=0 failed=1
Well, that didn't work.
But what if the variables are defined, but empty?
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
command: "rm -rf {{x}}/{{y}}"
vars:
x: ""
y: ""
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
ESTABLISH LOCAL CONNECTION FOR USER: root
localhost EXEC /bin/sh -c '( umask 22 && mkdir -p "` echo $HOME/.ansible/tmp/ansible-tmp-1461129132.63-211170666238105 `" && echo "` echo $HOME/.ansible/tmp/ansible-tmp-1461129132.63-211170666238105 `" )'
localhost PUT /tmp/tmp78m3WM TO /root/.ansible/tmp/ansible-tmp-1461129132.63-211170666238105/command
localhost EXEC /bin/sh -c 'LANG=en_US.UTF-8 LC_ALL=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 /usr/bin/python /root/.ansible/tmp/ansible-tmp-1461129132.63-211170666238105/command; rm -rf "/root/.ansible/tmp/ansible-tmp-1461129132.63-211170666238105/" > /dev/null 2>&1'
fatal: [localhost]: FAILED! => {"changed": true, "cmd": ["rm", "-rf", "/"], "delta": "0:00:00.001740", "end": "2016-04-20 05:12:12.668616", "failed": true, "invocation": {"module_args": {"_raw_params": "rm -rf /", "_uses_shell": false, "chdir": null, "creates": null, "executable": null, "removes": null, "warn": true}, "module_name": "command"}, "rc": 1, "start": "2016-04-20 05:12:12.666876", "stderr": "rm: it is dangerous to operate recursively on ‘/’\nrm: use --no-preserve-root to override this failsafe", "stdout": "", "stdout_lines": [], "warnings": ["Consider using file module with state=absent rather than running rm"]}
NO MORE HOSTS LEFT *************************************************************
to retry, use: --limit @killme.retry
PLAY RECAP *********************************************************************
localhost : ok=0 changed=0 unreachable=0 failed=1
Finally, some progress! But it still complains that I didn't use --no-preserve-root.
Of course, it also warns me that I should try using the file module and state=absent. Let's see if that works.
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
file: path="{{x}}/{{y}}" state=absent
vars:
x: ""
y: ""
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
ESTABLISH LOCAL CONNECTION FOR USER: root
localhost EXEC /bin/sh -c '( umask 22 && mkdir -p "` echo $HOME/.ansible/tmp/ansible-tmp-1461129394.62-191828952911388 `" && echo "` echo $HOME/.ansible/tmp/ansible-tmp-1461129394.62-191828952911388 `" )'
localhost PUT /tmp/tmpUqLzyd TO /root/.ansible/tmp/ansible-tmp-1461129394.62-191828952911388/file
localhost EXEC /bin/sh -c 'LANG=en_US.UTF-8 LC_ALL=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 /usr/bin/python /root/.ansible/tmp/ansible-tmp-1461129394.62-191828952911388/file; rm -rf "/root/.ansible/tmp/ansible-tmp-1461129394.62-191828952911388/" > /dev/null 2>&1'
fatal: [localhost]: FAILED! => {"changed": false, "failed": true, "invocation": {"module_args": {"backup": null, "content": null, "delimiter": null, "diff_peek": null, "directory_mode": null, "follow": false, "force": false, "group": null, "mode": null, "original_basename": null, "owner": null, "path": "/", "recurse": false, "regexp": null, "remote_src": null, "selevel": null, "serole": null, "setype": null, "seuser": null, "src": null, "state": "absent", "validate": null}, "module_name": "file"}, "msg": "rmtree failed: [Errno 16] Device or resource busy: '/boot'"}
NO MORE HOSTS LEFT *************************************************************
to retry, use: --limit @killme.retry
PLAY RECAP *********************************************************************
localhost : ok=0 changed=0 unreachable=0 failed=1
Good news, everyone! It started trying to delete all my files! But unfortunately it ran into an error. I'll leave fixing that and getting the playbook to destroy everything using the file module as an exercise to the reader.
DO NOT run any playbooks you see beyond this point! You'll see why in a moment.
Finally, for the coup de grâce...
[root@diaf ~]# cat killme.yml
---
- hosts: localhost
gather_facts: False
tasks:
- name: Die in a fire
raw: "rm -rf {{x}}/{{y}}"
vars:
x: ""
y: "*"
[root@diaf ~]# ansible-playbook -l localhost -vvv killme.yml
Using /etc/ansible/ansible.cfg as config file
1 plays in killme.yml
PLAY ***************************************************************************
TASK [Die in a fire] ***********************************************************
task path: /root/killme.yml:5
ESTABLISH LOCAL CONNECTION FOR USER: root
localhost EXEC rm -rf /*
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/ansible/executor/process/result.py", line 102, in run
File "/usr/lib/python2.7/site-packages/ansible/executor/process/result.py", line 76, in _read_worker_result
File "/usr/lib64/python2.7/multiprocessing/queues.py", line 117, in get
ImportError: No module named task_result
This VM is an ex-parrot!
Interestingly, the above failed to do anything with command instead of raw. It just printed the same warning about using file with state=absent.
I'm going to say that it appears that if you aren't using raw that there is some protection from rm gone amok. You should not rely on this, though. I took a quick look through Ansible's code, and while I found the warning, I did not find anything that would actually suppress running the rm command.
Solution 2:
Will Ansible prevent the execution of rm -rf / in a shell script?
I did inspect the coreutils rm source, which has the following:
if (x.recursive && preserve_root)
{
static struct dev_ino dev_ino_buf;
x.root_dev_ino = get_root_dev_ino (&dev_ino_buf);
if (x.root_dev_ino == NULL)
error (EXIT_FAILURE, errno, _("failed to get attributes of %s"),
quoteaf ("/"));
}
The only way to wipe from the root is to get past this code block. From this source:
struct dev_ino *
get_root_dev_ino (struct dev_ino *root_d_i)
{
struct stat statbuf;
if (lstat ("/", &statbuf))
return NULL;
root_d_i->st_ino = statbuf.st_ino;
root_d_i->st_dev = statbuf.st_dev;
return root_d_i;
}
I interpret this to mean that the the function get_root_dev_ino returns null on /, and thus rm fails.
The only way to bypass the first code block (with recursion) is to have --no-preserve-root and it does no use an environment variable to override, so it would have to be passed explicitly to rm.
I believe this proves that unless Ansible explicitly passes --no-preserve-root to rm, it will not do this.
Conclusion
I do not believe that Ansible explicitly prevents rm -rf / because rm itself prevents it.