[Freeipa-devel] [PATCH 477] spec file: Add Requires(pre) on selinux-policy

Tue Aug 25 19:25:25 UTC 2015

On 08/25/2015 09:22 PM, Alexander Bokovoy wrote:
> On Tue, 25 Aug 2015, Martin Kosek wrote:
>> On 08/25/2015 08:59 PM, Alexander Bokovoy wrote:
>>> On Tue, 25 Aug 2015, Martin Kosek wrote:
>>>> On 08/25/2015 05:37 PM, Alexander Bokovoy wrote:
>>>>> On Tue, 25 Aug 2015, Martin Kosek wrote:
>>>>>> On 08/25/2015 04:37 PM, Jan Cholasta wrote:
>>>>>>> On 25.8.2015 14:50, Alexander Bokovoy wrote:
>>>>>>>> On Tue, 25 Aug 2015, Jan Cholasta wrote:
>>>>>>>>> On 25.8.2015 14:23, Alexander Bokovoy wrote:
>>>>>>>>>> On Tue, 25 Aug 2015, Jan Cholasta wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>>
>>>>>>>>>>> the attached patch fixes
>>>>>>>>>>> <https://fedorahosted.org/freeipa/ticket/5256>.
>>>>>>>>>>>
>>>>>>>>>>> Honza
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Jan Cholasta
>>>>>>>>>>
>>>>>>>>>>> From 216be8de30747f80f490d4e91a7cca4af3e767d6 Mon Sep 17 00:00:00 2001
>>>>>>>>>>> From: Jan Cholasta <jcholast at redhat.com>
>>>>>>>>>>> Date: Tue, 25 Aug 2015 14:14:25 +0200
>>>>>>>>>>> Subject: [PATCH] spec file: Add Requires(pre) on selinux-policy
>>>>>>>>>>>
>>>>>>>>>>> This prevents ipa-server-upgrade failures on SELinux AVCs because of
>>>>>>>>>>> old
>>>>>>>>>>> selinux-policy version.
>>>>>>>>>>>
>>>>>>>>>>> https://fedorahosted.org/freeipa/ticket/5256
>>>>>>>>>>> ---
>>>>>>>>>>> freeipa.spec.in | 1 +
>>>>>>>>>>> 1 file changed, 1 insertion(+)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/freeipa.spec.in b/freeipa.spec.in
>>>>>>>>>>> index cba91fe..fd73cda 100644
>>>>>>>>>>> --- a/freeipa.spec.in
>>>>>>>>>>> +++ b/freeipa.spec.in
>>>>>>>>>>> @@ -139,6 +139,7 @@ Requires: systemd-units >= 38
>>>>>>>>>>> Requires(pre): shadow-utils
>>>>>>>>>>> Requires(pre): systemd-units
>>>>>>>>>>> Requires(post): systemd-units
>>>>>>>>>>> +Requires(pre): selinux-policy >= %{selinux_policy_version}
>>>>>>>>>>> Requires: selinux-policy >= %{selinux_policy_version}
>>>>>>>>>>> Requires(post): selinux-policy-base
>>>>>>>>>>> Requires: slapi-nis >= 0.54.2-1
>>>>>>>>>> If we have it in Requires(pre), we don't need it in Requires, as
>>>>>>>>>> Requires(pre) is a superset of guarantees that Requires gives you.
>>>>>>>>>
>>>>>>>>> Martin (CCed) told me Requires(pre) does not imply Requires.
>>>>>>>> See http://rpm.org/api/4.4.2.2/tsort.html (available since 2007):
>>>>>>>> ----------------
>>>>>>>> Since the only way out of a dependency loop is to snip the loop
>>>>>>>> somewhere, rpm uses hints from Requires: dependencies to distinguish
>>>>>>>> co-requisite (these are not needed to install, only to use, a package)
>>>>>>>> from pre-requisite (these are guaranteed to be installed before the
>>>>>>>> package that includes the dependency) relations.
>>>>>>>> ----------------
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Requires(pre) ensures that selinux-policy of specific version is
>>>>>>>>>> installed before pre scripts of freeipa-server would run, be it in the
>>>>>>>>>> same transaction or in a previous one.
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Hmm, ipa-server-upgrade is run in posttrans. Should the Requires(pre)
>>>>>>>>> be changed to Required(posttrans)?
>>>>>>>> I don't think there is posttrans target. Perhaps, we can just make sure
>>>>>>>> Requires(post) is enough.
>>>>>>>
>>>>>>> OK, let's try that. Updated patch attached.
>>>>>>>
>>>>>>
>>>>>> Will this really make a difference? I thought the problem is caused by
>>>>>> selinux-policy being installed after freeipa-server package upgrade. We
>>>>>> already
>>>>>> have Requires on selinux-policy, so I am not sure what is actually
>>>>>> changed by
>>>>>> this patch.
>>>>> The change is that with Requires(pre) or Requires(post) we are
>>>>> guaranteed that selinux-policy is installed and available before our pre
>>>>> or post scriptlets are run. With Requires only we are not guaranteed to
>>>>> be installed after selinux-policy, only that it would be available as
>>>>> part of the same transaction we are installed in.
>>>>>
>>>>> We don't really need to have Requires(pre) because we don't rely on
>>>>> selinux-policy being available in pre scriptlet. Forcing Requires(pre)
>>>>> doesn't help anyone else (rpm/yum/dnf need to solve dependency loops and
>>>>> we are only complicating with Requires(pre) if we don't actually need
>>>>> it). Thus, choosing Require(post) is more correct from distribution
>>>>> point of view.
>>>>
>>>> Sure, but given that FreeIPA upgrade is run in the posttrans phase:
>>>>
>>>> %posttrans server
>>>> # This must be run in posttrans so that updates from previous
>>>> # execution that may no longer be shipped are not applied.
>>>> /usr/sbin/ipa-server-upgrade --quiet >/dev/null || :
>>>>
>>>> I am now not sure how Requires(pre) or Requires(post) help here, in all
>>>> cases, the right selinux-policy should be there before all the posttrans
>>>> scripts are being run.
>>> I've looked at the rpm source code and here is the list of all supported
>>> requires/dependencies types:
>>> https://github.com/rpm-software-management/rpm/blob/140744377b019e0de81d76d0931c32228d2ed57e/build/rpmfc.c#L1056
>>>
>>>
>>>
>>> Requires(posttrans) is there so we could use this one too but it was
>>> added only in 4.12-alpha which means it is missing in RHEL/CentOS 7, for
>>> example, as they are only up to 4.11.
>>>> Maybe the new selinux-policy is required for certmonger itself or some other
>>>> event during upgrade?
>>> No, I don't think so. However, we cannot set Requires(posttrans), thus
>>> we should be using closest target before it, i.e. Requires(post).
>>
>> Thank you, but I think I still did not get an answer for my question.
>>
>> IIUC, the rough rpm process with regards to freeipa-server package upgrade,
>> it should be in this order:
>>
>> _
>> |
>> v
>> RPM installs some dependencies of freeipa-server
>> |
>> V
>> RPM installs "Requires(pre)" of freeipa-server
>> freeipa-server pre scriptlet runs
>> |
>> v
>> RPM installs freeipa-server
>> |
>> v
>> RPM installs "Requires(post)" of freeipa-server
>> freeipa-server post scriptlet runs
>> |
>> v
>> RPM installs some dependencies of freeipa-server
>> |
>> v
>> RPM executes posttrans scriptlets, including "ipa-server-upgrade".
> The flow above is not correct. Each scriptlet of the package is executed
> when package is installed. In particular, there is no period of waiting
> until end of whole transaction to start executing %posttrans scriptlet of
> a specific package. RPM only guarantees you that %posttrans scriptlet is
> executed as the last thing of this package intall, after all
> %post/%postun scriptlets were executed for this package and all triggers
> for affected packages were executed.

Ah, so this was the key misunderstanding I was having. I thought that all 
posttrans scripts for all packages are run in the end.

>
> This does not guarantee that selinux-policy processing would be before
> freeipa-server processing unless we explicitly ask for the ordering via
> Requires(<stage>) tag. The order of processing packages is affected by
> Requires(<stage>) tag, but processing of each single package is still
> sequential.
>
>> My question is, if all the magic happens in the last step, how does adding
>> (pre) or (post) Requires help, given we already have the "normal" Requires?
> Because with Requires nothing guarantees selinux-policy is
> installed before freeipa-server in the same transaction, we have to use
> Requires(<stage>) that would ensure we have the selinux-policy
> installation/upgrade completed by the time that stage is reached in
> freeipa-server installation/upgrade process. In reality Requires(pre) is
> often enough too but not recommended as it also could cause loop
> breaking issues.
>

Thanks for the explanation. If this is the case, the patch should be OK as is 
indeed and Requires on post should be enough.