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Description of problem:
The Selinux policy for dhcpd doesn't support on commit scripts.
For more details on on-commit scripts see:
http://jpmens.net/2011/07/06/execute-a-script-when-isc-dhcp-hands-out-a-new-lease/
Version-Release number of selected component (if applicable):
dhcp-4.2.5-42.el7
How reproducible:
Steps to Reproduce:
1. Enable an on-commit script
2. check the audit log
3. there is no step 3
Actual results:
type=AVC msg=audit(1453792866.181:11697): avc: denied { execute } for pid=3174 comm="dhcpd" name="myscript" dev="dm-0" ino=147660 scontext=system_u:system_r:dhcpd_t:s0 tcontext=unconfined_u:object_r:dhcp_etc_t:s0 tclass=file
Expected results:
A valid selinux file context for on commit scripts which allows execution, documented in dhcpd_selinux (8)
Additional info:
The samba reference policy provides a good example of what would be needed for dhcpd.
optional_policy(`
type samba_unconfined_script_t;
type samba_unconfined_script_exec_t;
domain_type(samba_unconfined_script_t)
domain_entry_file(samba_unconfined_script_t, samba_unconfined_script_exec_t)
corecmd_shell_entry_type(samba_unconfined_script_t)
role system_r types samba_unconfined_script_t;
allow smbd_t samba_unconfined_script_exec_t:dir search_dir_perms;
allow smbd_t samba_unconfined_script_exec_t:file ioctl;
unconfined_domain(samba_unconfined_script_t)
tunable_policy(`samba_run_unconfined',`
domtrans_pattern(smbd_t, samba_unconfined_script_exec_t, samba_unconfined_script_t)
',`
can_exec(smbd_t, samba_unconfined_script_exec_t)
')
')
There doesn't seem to be a default location, a subdir below /etc/dhcp would make sense I guess. I've opted for '/etc/dhcp/scripts' but am happy to change to a better option.
+1 to something below /etc/dhcp/
We already have /etc/dhcp/dhclient.d/ for dhclient-related scripts, so my first thought was /etc/dhcp/dhcpd.d/
But then I realized that the execute() statement can be used not only with dhcpd but with dhclient as well, because the RELNOTES says:
"This permits dhcpd or dhclient to execute a named external program
with command line arguments specified from other configuration language."
Also as dhclient-script(8) says the additional dhclient-{enter/exit/up/down}-hooks scripts that further extend dhclient-script's functionality should be placed into /etc/dhcp/
So maybe just the /etc/dhcp/ without any additional subdirectory ?
The AVC I got is shown in my initial report:
type=AVC msg=audit(1453792866.181:11697): avc: denied { execute } for pid=3174 comm="dhcpd" name="myscript" dev="dm-0" ino=147660 scontext=system_u:system_r:dhcpd_t:s0 tcontext=unconfined_u:object_r:dhcp_etc_t:s0 tclass=file
However this does show that the file is labelled as dhcp_etc_t, which is the default for /etc/dhcp. When I change the context to bin_t the on-commit script indeed works.
> chcon -t bin_t /etc/dhcp/myscript.py
> ls -aZ /etc/dhcp/myscript.py
-rwxr-xr-x. root root unconfined_u:object_r:bin_t:s0 /etc/dhcp/myscript.py
Is this recommended type for dhcp script documented somewhere? Should it be?
OK, O overlooked.
The problem is /etc/dhcp is a directory for config files. It would be great to have subdir for these scripts.
We can define a generic labeling for /etc/dhcp to have bin_t as a default label and have more specific labels for config files. But I don't see it as a good solution.
(In reply to Sten Spans from comment #10)
> /etc/dhcp/scripts would make the most sense.
>
> Running scripts is possible for expiry and release as well, so hard-coding
> "commit" in the directory name doesn't really seem logical.
>
> https://deepthought.isc.org/article/AA-01094/0/Adding-support-for-on-commit-
> on-expire-and-on-release-statements-in-DHCPv6.html
Ok do you need a bug?
(In reply to Lukas Vrabec from comment #12)
> I'll add bin_t label for /etc/dhcp/scripts.
OK
> Jiri, what is state of this issue from your side?
I haven't changed anything in dhcp.
Pavel, I think we should add the /etc/dhcp/scripts/ with just README saying that it's a directory for on-commit scripts.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHBA-2016-2283.html