Can I rewaken $CFG->dirroot?

Can I rewaken $CFG->dirroot?

by Visvanath Ratnaweera -
Number of replies: 8
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In the old days there was a $CFG->dirroot which pointed to the Moodle code directory. It became obsolete since Moodle finds it out from the HTTP request. Can I rewaken the old dirroot?

I saw that $CFG->dirroot is used in the code for various things. My "dirroot" could have a different name. The question is, can I set $CFG->something to a directory, so that Moodle will take that directory as its root? Without causing a major upset in the code, I mean.
wink

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In reply to Visvanath Ratnaweera

Re: Can I rewaken $CFG->dirroot?

by Davo Smith -
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I'm not quite sure what you mean by "in the old days" - $CFG->dirroot still points at the code directory and has never stopped doing so (unless there is something very strange that I've been missing every time I've used it).
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In reply to Visvanath Ratnaweera

Re: Can I rewaken $CFG->dirroot?

by Dan Marsden -
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you know you've been around for a while when you are still setting dirroot in config.php smile - it's been ignored in config.php since Moodle 2.0 as part of MDL-22546

it doesn't get it from the http request - in 3.2 versions and higher it uses the PHP predefined constant __DIR__ - it older versions 2.0 -> 3.1 it used dirname().

So - you can set it in config.php but it will just get ignored/overwritten.

I just checked my local machine and our deployment scripts and we're still setting $CFG->dirroot in some of our config.php files here - might get round to stripping that out at some point...
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In reply to Visvanath Ratnaweera

Re: Can I rewaken $CFG->dirroot?

by Visvanath Ratnaweera -
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Many thanks for your time (while I was sleeping)!
wink

@Davo, my understanding is that one can set a $CFG->dirroot, but since Moodle 2.x it will be ignored!

@Dan, MDL-22546 - what a short and sweet trouble ticket!

Thanks for the correction - PHP dirname() and __DIR__. So the short answer is, since Moodle 2.x no point in setting a $CFG->dirroot.

But there is hope, what I wanted to might work without a (forced) dirroot. Need to do some testing.

@Ken, the Why? I was trying to find the best answer for a support enquiry (and learning on the way). The scenario requires a fleet of very small Moodle instances, kind of low cost create and delete Moodle sites. Reminded me of a trick some installers do, keep one code directory and separate the database and moodledata by checking the HTTP_HOST web server (in this case Nginx) variable.

I know, I know, Docker is the answer. This is a low profile, low prio enquiry. Paradigm changes can wait.
smile

@all, I know that short-cut breaks PHP CLI scripts. Apart from that was there a security issue?
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In reply to Visvanath Ratnaweera

Re: Can I rewaken $CFG->dirroot?

by Dan Marsden -
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yeah - a few people try to use HTTP_HOST to build wwwroot in the config.php - take a look at some of the complaints from people using bluehost as a provider - you run into all sorts of issues.

The biggest gotcha is that if you use HTTP_HOST you must not do anything with Moodle via CLI - as the http_host doesn't exist. That includes things like Cron/upgrade/install/deployment scripts etc - if you run cron on the cli with http_host, bad things happen to emails and you end up with broken links being sent to end users - also other edge cases like saml2 authentication won't work correctly when you're using HTTP_HOST.
Also - make sure you don't set "pathtophp" - as that's basically the same as letting things run on the cli....

I heard of a Moodle site that accidentally broke their production site completely because they ran an upgrade via cli on a staging site, and it picked the prod db because it was using some hacks based on HTTP_HOST - their site was down for about 4 weeks while they tried to restore it all from backups.

So - if you do go down that track... be really really really careful.... smile
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In reply to Dan Marsden

Re: Can I rewaken $CFG->dirroot?

by Visvanath Ratnaweera -
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Hi Dan

> if you do go down that track... be really really really careful....
smile

Seriously, I can follow the dangers you described in clear detail, and remember myself warning others. For the experiment I am doing, for "a fleet of very small Moodle instances, kind of low cost create and delete Moodle sites", the stakes are not high.

I did a quick test and can confirm that there is no point in setting $CFG->dirroot in config.php. It is overwritten. It is the "require_once(__DIR__ . '/lib/setup.php');" line in config.php doing this, I suppose. Anyway, setting wwwroot from HTTP_HOST and assigning different databases, dataroots, etc. works the way, I wanted, without worrying about dirroot. It is also clear, there is only one Moodle directory tree.

What I would like to know is whether there are documented security issues in this approach.
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In reply to Visvanath Ratnaweera

Re: Can I rewaken $CFG->dirroot?

by Dan Marsden -
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You'd probably want to check http_host against a list of known domains.. and validate/sanitize it - theoretically a user could add a local entry for moodle.org pointing at your server IP address (or a domain they control) and if they can also trigger cron, could make it send email from your server with their domain in various links.

I can think of a few ways I could attack the security of a site by getting it to use a domain I have control over.

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In reply to Dan Marsden

Re: Can I rewaken $CFG->dirroot?

by Visvanath Ratnaweera -
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Hi Dan

Got it! Sure I will react only to "my" domains, i.e. validate/sanitize HTTP_HOST.

Relieved to know that there are no other simple attacks. I am not worried about sophisticated attacks. This is for a less privileged / less demanding group - and the domain (it'll be sub-domains of a single main domain) won't be mine. Will pass a full danger report to them and get their written OK as a promise not to complain.

From what I saw in my quick test today, this approach will be very valuable to them. Good Karma is never lost.
wink
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