Оvercommit - convenient Git hook manager

Voldemar Duletskiy, Ruby developer, Evrone, Moscow Ruby Meet-up 6 report
01 August 2017   3008

Dynamic, open source programming language with a focus on simplicity and productivity, it has an elegant syntax that is natural to read and easy to write.

Hello Ruby fans! Today we will talk about Overcommit - the convenient management of git-hooks.

Imagine that you have a small project with a micro-team of three or four people, including the manager. Deadline is near, but you cannot lower the quality of the code. You don't wanna use CI and there are no extra money for it.

What is hooks and where are they located?

It is the scripts that are executed at certain event. You can view all existing hooks by running the following command:

ls -la .git/hooks

You will see this listing:

-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 commit-msg
-rwxr-xr-x   1 voldemar  staff  3755 28 июн 16:39 overcommit-hook
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 post-checkout
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 post-commit
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 post-merge
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 post-rewrite
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 pre-commit
-rwxr-xr-x   1 voldemar  staff   673  2 Jun 14:37 pre-commit.sh
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 pre-push
-rwxr-xr-x   1 voldemar  staff  3755 28 Jun 16:39 pre-rebase

Hook is an executable file, which can content anything, including the Ruby code.

Why it is cool?

  • You can put linters like rubocop to the pre-commit hooks. It will not allow you to commit substandard code
  • You can hang up rspec to the pre-push hooks, and if the tests are dropped - cancel code sending
  • If you are already actively using hooks - you don't need to drag them from one repository to another, they all lie in .ovecommit.yml in a convenient format

Ruby static code analyzer, based on the community Ruby style guide

If you suffer from dispersion and you are sick of messages from your CI that tests have dropped again, or the ruby-cop found a million syntactic violations (or your colleagues in the code-review process). If you are an experienced developer, a good set of hooks seriously discourages young developers and reduces your code-review time. 



gem 'overcommit'

Execude from the consol:

bundle exec overcommit --install

 Now let's edit .overcommit.yml file

    enabled: true
    command: ['bin/bundle', 'exec', 'rubocop', '-R']
    on_warn: fail
    enabled: true
    command: ['bin/bundle', 'exec', 'haml-lint', 'app/views/']
    on_warn: fail
    enabled: true
    command: ['bin/bundle', 'exec', 'scss-lint']
    include: 'app/assets/**/*.scss'
    on_warn: fail

    enabled: true

We can see here that the launch of the rubocop scripts is describled in nice forman. haml-linter, sccs-linter and tests runs just before the commit.

In order to enforce hook running this should be executed:

bundle exec overcommit -R

Now, with every attempt to commit something, checks will be performed firstly.


Underwater rocks

If there are a lot of tests or they are dropping randomly - if you already have a habit to brew coffee while test runs, it's better to chop the hook responsible for running the tests. If they fall randomly - fix the tests at last, damn it.

Integration with Rubymine - I have serious problems with the integration of Overcommit and Rubymine

Continuous Integration

The practice of merging all developer working copies to a shared mainline several times a day

Overcommit and CI integration - if you still decide to connect CI, then most likely it already provides validation for the code. Often, their rules don't match and you have to adjust the settings, for example Rubocop under CI, or vice versa.

You can skip hooks by running git commit --no-verify


Overcommit is an excellent utility for maintaining a project in good shape for small teams. It will allow you not to grab your head every time after creating a pool of the requester with exclamations "Damn, I forgot to use rubocop again!" or "Damn, all the tests fell!".

Backdoor to be Found in Bootstrap-sass Ruby Gem

Backdoor has been added to the, published March 26 in the RubyGems repository and issue is resolved in release, proposed on April 3rd
05 April 2019   545

Backdoor (CVE-2019-10842) was detected in the popular Ruby-library bootstrap-sass (Bootstrap 3 option with Sass support), which has about 28 million downloads, allowing attackers to execute their code on servers running projects using bootstrap-sass . The backdoor has been added to release, published March 26 in the RubyGems repository. The issue is resolved in release, proposed on April 3rd.

The backdoor was hiddenly added to the lib/active-controller/middleware.rb, in which the code for calling eval appeared with the value passed through the cookie"___ cfduid =". For an attack, it was enough to send a request to the server, setting thecookie "___cfduid" and pass as an argument the commands encoded in Base64 format. The name of the cookie "___cfduid" was chosen for camouflage under thecookie "__cfduid", set by CDN Cloudflare and characterized by the presence of two underscores instead of three.

It is noteworthy that the malicious code was published only in the final package published in the RubyGems repository, but was not included in the source code in the Git repository. The source code of the library remained correct and did not arouse suspicion among developers, which underscores the importance of using repeatable builds and implementing a process to verify the compliance of published packages with reference sources. Apparently, the attack was carried out through the seizure of the account parameters to RubyGems from one of the two library maintainers (officially the leakage of account data has not yet been confirmed).

The attackers showed prudence and built the backdoor not into the latest 3.4.x branch, the latest release of which has more than 217,000 downloads, but as an update for the previous 3.2.x branch, relying on the fact that corrective update of dependency will not cause suspicion. A rough estimate of the 1670 repositories on GitHub use bootstrap-sass as a dependency and applications associated with these repositories can potentially be compromised. Developers are advised to trace the use of the bootstrap-sass library among indirect dependencies and check whether the automatic upgrade to the backdoor version has been performed. Judging by the statistics of the RubyGems package, the backdoor package was downloaded about 1,500 times.

Information about a possible backdoor was published in the bug tracking system a few hours after placing the problematic release, after which the maintainers removed the problematic release from RubyGems about an hour later and changed their login passwords, but did not take into account that the removed versions could remain for several days on the mirrors. On April 3, an additional release was created, completely analogous to version, which made it possible to get rid of the version with backdoor without switching to a new branch 3.4.