GitLab UI not reporting stderr with pre-receive custom_hooks

Summary

I have a pre-receive custom hook installed on my GitLab repo, the enforces a particular commit pattern, eg "JIRA-ID: message" I get a 500 Internal Server error when committing a change in the GitLab UI (by editing a file in the browser and committing changes from there), and a "Something went wrong with merge" error when clicking Merge button in a merge request, if the commit message does not meet the requirements.

Steps to reproduce

  • Create a repo
  • Click the README file in the files list, and click to Edit the contents. Make a random change to the text.
  • Leave the Commit message as it is, eg. "Update README.md" so that it doesn't meet the requirements enforced by the pre-receive hook
  • Click "Commit changes"
  • You get a 500 Whoops something went wrong on our end

OR

  • Create a merge request from a branch that has changes.
  • In the Merge Request screen in GitLab, modify the commit message so that it doesn't meet the requirements enforced by the pre-receive hook
  • Click the Merge button to merge
  • You get a message next to the Merge button "Something went wrong with merge". The page refreshes after 10 seconds and the message disappears. The same happens if you click Merge again.

The pre-receive hook writes the message that is supposed to inform the user that their commit message doesn't meet the requirements to stderr. I would expect this text to be relayed on the GitLab UI web page rather than a 500 server error or a simple "Something went wrong with merge" error.

production.log output for 500 error in the GitLab UI:

Started POST "/api/v4/internal/allowed" for 127.0.0.1 at 2018-11-09 20:58:42 +0000
Completed 500 Internal Server Error in 458ms (ActiveRecord: 5.2ms | Elasticsearch: 0.0ms)

RuntimeError (can't modify frozen String):
  lib/gitlab/utils.rb:32:in `nlbr'
  lib/gitlab/git/pre_receive_error.rb:17:in `nlbr'
  lib/gitlab/git/pre_receive_error.rb:9:in `initialize'
  lib/gitlab/gitaly_client/operation_service.rb:266:in `exception'
  lib/gitlab/gitaly_client/operation_service.rb:266:in `raise'

▽
  lib/gitlab/gitaly_client/operation_service.rb:266:in `user_commit_files'
  lib/gitlab/git/repository.rb:792:in `block in multi_action'
  lib/gitlab/git/repository.rb:862:in `wrapped_gitaly_errors'
  lib/gitlab/git/repository.rb:791:in `multi_action'
  app/models/repository.rb:818:in `block in multi_action'
  app/models/repository.rb:801:in `with_cache_hooks'
  app/models/repository.rb:818:in `multi_action'
  app/models/repository.rb:791:in `update_file'
  app/services/files/update_service.rb:6:in `create_commit!'
  app/services/commits/create_service.rb:21:in `execute'
  app/controllers/concerns/creates_commit.rb:25:in `create_commit'
  app/controllers/projects/blob_controller.rb:65:in `update'
  lib/gitlab/i18n.rb:53:in `with_locale'
  lib/gitlab/i18n.rb:59:in `with_user_locale'
  app/controllers/application_controller.rb:432:in `set_locale'
  lib/gitlab/middleware/multipart.rb:101:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  ee/lib/gitlab/jira/middleware.rb:15:in `call'
  lib/gitlab/middleware/go.rb:17:in `call'
  lib/gitlab/etag_caching/middleware.rb:11:in `call'
  lib/gitlab/middleware/read_only/controller.rb:40:in `call'
  lib/gitlab/middleware/read_only.rb:16:in `call'
  lib/gitlab/middleware/basic_health_check.rb:25:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
  lib/gitlab/middleware/release_env.rb:10:in `call'

Error in log when doing merge request:

MergeService ERROR: core/server!9 - can't modify frozen String
Expand for output related to GitLab environment info 
System information
System:
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.4.5p335
Gem Version:	2.7.6
Bundler Version:1.16.2
Rake Version:	12.3.1
Redis Version:	3.2.12
Git Version:	2.18.1
Sidekiq Version:5.2.1
Go Version:	unknown


GitLab information
Version:	11.4.5-ee
Revision:	bf6db46
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.8
URL:		https://gitlab.red61.com
HTTP Clone URL:	https://gitlab.red61.com/some-group/some-project.git
SSH Clone URL:	git@gitlab.red61.com:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers:


GitLab Shell
Version:	8.3.3
Repository storage paths:
  • default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git
Expand for output related to the GitLab application check 
Checking GitLab Shell ...


GitLab Shell version >= 8.3.3 ? ... OK (8.3.3)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
2/6 ... ok
2/7 ... ok
8/8 ... ok
8/9 ... ok
8/10 ... ok
2/12 ... ok
2/13 ... ok
2/14 ... ok
2/15 ... ok
8/16 ... ok
17/17 ... ok
2/19 ... ok
17/20 ... ok
2/21 ... ok
17/22 ... ok
2/23 ... ok
2/24 ... ok
2/25 ... ok
2/26 ... ok
16/27 ... ok
17/28 ... ok
2/29 ... ok
17/30 ... ok
17/31 ... ok
17/32 ... ok
17/33 ... ok
17/34 ... ok
17/35 ... ok
17/36 ... ok
17/37 ... ok
17/38 ... ok
17/39 ... ok
2/41 ... ok
17/42 ... ok
16/43 ... ok
17/44 ... ok
17/45 ... ok
17/46 ... ok
17/47 ... ok
17/48 ... ok
2/49 ... ok
17/50 ... ok
2/51 ... ok
17/52 ... ok
17/53 ... ok
20/54 ... ok
20/55 ... ok
20/56 ... ok
17/58 ... ok
20/59 ... ok
20/60 ... ok
20/61 ... ok
20/62 ... ok
21/64 ... ok
17/66 ... ok
20/67 ... ok
2/68 ... ok
17/69 ... repository is empty
2/70 ... ok
17/71 ... ok
22/72 ... ok
17/73 ... ok
17/74 ... ok
17/75 ... ok
2/76 ... ok
2/77 ... ok
8/78 ... ok
2/79 ... ok
17/81 ... ok
8/82 ... ok
20/83 ... ok
2/84 ... ok
8/85 ... ok
4/86 ... ok
17/87 ... ok
2/89 ... ok
2/90 ... ok
4/91 ... repository is empty
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK


Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Sidekiq ...


Running? ... yes
Number of Sidekiq processes ... 1


Checking Sidekiq ... Finished


Reply by email is disabled in config/gitlab.yml
Checking LDAP ...


LDAP is disabled in config/gitlab.yml


Checking LDAP ... Finished


Checking GitLab ...


Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
2/6 ... yes
2/7 ... yes
8/8 ... yes
8/9 ... yes
8/10 ... yes
2/12 ... yes
2/13 ... yes
2/14 ... yes
2/15 ... yes
8/16 ... yes
17/17 ... yes
2/19 ... yes
17/20 ... yes
2/21 ... yes
17/22 ... yes
2/23 ... yes
2/24 ... yes
2/25 ... yes
2/26 ... yes
16/27 ... yes
17/28 ... yes
2/29 ... yes
17/30 ... yes
17/31 ... yes
17/32 ... yes
17/33 ... yes
17/34 ... yes
17/35 ... yes
17/36 ... yes
17/37 ... yes
17/38 ... yes
17/39 ... yes
2/41 ... yes
17/42 ... yes
16/43 ... yes
17/44 ... yes
17/45 ... yes
17/46 ... yes
17/47 ... yes
17/48 ... yes
2/49 ... yes
17/50 ... yes
2/51 ... yes
17/52 ... yes
17/53 ... yes
20/54 ... yes
20/55 ... yes
20/56 ... yes
17/58 ... yes
20/59 ... yes
20/60 ... yes
20/61 ... yes
20/62 ... yes
21/64 ... yes
17/66 ... yes
20/67 ... yes
2/68 ... yes
17/69 ... yes
2/70 ... yes
17/71 ... yes
22/72 ... yes
17/73 ... yes
17/74 ... yes
17/75 ... yes
2/76 ... yes
2/77 ... yes
8/78 ... yes
2/79 ... yes
17/81 ... yes
8/82 ... yes
20/83 ... yes
2/84 ... yes
8/85 ... yes
4/86 ... yes
17/87 ... yes
2/89 ... yes
2/90 ... yes
4/91 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.5)
Git version >= 2.9.5 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 13
Elasticsearch version 5.1 - 5.5? ... skipped (elasticsearch is disabled)


Checking GitLab ... Finished