A user can approve the same merge request multiple times

Summary

You can approve the same merge request multiple times if you click fast enough.

Steps to reproduce

1. Navigate to the merge request you want to approve
2. pkill firefox -STOP
3. Click on the 'Approve' button multiple times
4. pkill firefox -CONT

It also works through the API or by clicking really fast. A colleague wrote a script for this.

Example Project

Any project with MRs and approval.

What is the current bug behavior?

Clicking the button or calling the api to approve a MR fast enough approves the MR multiple times.

What is the expected correct behavior?

Clicking the button or calling the api to approve a MR fast enough should still only approves the MR once.

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:		
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.4.4p296
Gem Version:	2.7.6
Bundler Version:1.16.2
Rake Version:	12.3.1
Redis Version:	3.2.11
Git Version:	2.17.1
Sidekiq Version:5.1.3
Go Version:	unknown
GitLab information
Version:	11.0.4-ee
Revision:	3350cd6
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.8
URL:		http://10.100.0.1:8000
HTTP Clone URL:	http://10.100.0.1:8000/some-group/some-project.git
SSH Clone URL:	git@10.100.0.1:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	no
GitLab Shell
Version:	7.1.4
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab Shell ...
GitLab Shell version >= 7.1.4 ? ... OK (7.1.4)
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: ...
2/1 ... ok
2/2 ... ok
2/3 ... ok
2/4 ... ok
2/5 ... ok
2/6 ... ok
2/7 ... ok
2/8 ... ok
2/9 ... ok
2/10 ... ok
2/11 ... ok
2/12 ... ok
2/13 ... ok
2/14 ... ok
2/15 ... ok
2/16 ... ok
2/17 ... ok
2/18 ... ok
2/19 ... ok
2/20 ... ok
2/21 ... ok
2/22 ... ok
2/23 ... ok
2/24 ... ok
2/25 ... ok
12/26 ... ok
12/27 ... ok
12/28 ... ok
12/29 ... ok
12/30 ... ok
12/31 ... ok
12/32 ... ok
12/33 ... ok
12/34 ... ok
12/35 ... ok
12/36 ... ok
12/37 ... ok
12/38 ... ok
12/39 ... ok
12/40 ... ok
12/41 ... ok
12/42 ... ok
12/43 ... ok
12/44 ... ok
12/45 ... ok
2/46 ... ok
12/47 ... ok
12/48 ... ok
12/49 ... ok
12/50 ... ok
12/51 ... ok
6/52 ... ok
6/53 ... ok
12/54 ... ok
12/55 ... ok
12/56 ... ok
12/57 ... ok
6/59 ... ok
6/60 ... ok
6/61 ... ok
12/62 ... ok
12/63 ... ok
1/64 ... ok
1/65 ... ok
12/67 ... ok
1/68 ... ok
8/69 ... repository is empty
12/70 ... ok
12/71 ... ok
6/72 ... ok
11/74 ... ok
2/75 ... ok
11/77 ... ok
7/78 ... ok
16/79 ... ok
2/80 ... ok
6/81 ... ok
11/82 ... ok
5/83 ... ok
2/85 ... ok
2/86 ... ok
8/87 ... ok
19/88 ... ok
19/89 ... ok
5/90 ... ok
1/91 ... ok
19/93 ... ok
2/94 ... ok
10/95 ... ok
2/97 ... ok
11/98 ... ok
2/99 ... ok
2/101 ... ok
2/102 ... ok
2/103 ... ok
26/104 ... ok
16/105 ... ok
2/109 ... ok
2/110 ... ok
2/111 ... ok
16/112 ... ok
2/113 ... ok
2/114 ... ok
5/116 ... ok
2/117 ... repository is empty
16/118 ... ok
2/119 ... ok
6/120 ... ok
5/121 ... ok
16/122 ... ok
2/123 ... ok
2/124 ... ok
6/125 ... ok
16/127 ... ok
2/128 ... ok
2/129 ... ok
5/130 ... ok
5/131 ... ok
6/132 ... ok
6/133 ... ok
6/134 ... ok
2/135 ... ok
2/136 ... ok
6/139 ... ok
2/140 ... ok
16/141 ... ok
2/146 ... ok
2/147 ... ok
2/148 ... ok
2/149 ... ok
6/150 ... ok
2/151 ... ok
2/152 ... ok
16/154 ... ok
16/155 ... ok
2/156 ... ok
2/158 ... ok
16/159 ... ok
35/160 ... ok
35/161 ... ok
2/162 ... ok
2/163 ... ok
23/164 ... ok
2/166 ... ok
2/167 ... ok
5/168 ... ok
2/169 ... ok
2/170 ... ok
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: ...
2/1 ... yes
2/2 ... yes
2/3 ... yes
2/4 ... yes
2/5 ... yes
2/6 ... yes
2/7 ... yes
2/8 ... yes
2/9 ... yes
2/10 ... yes
2/11 ... yes
2/12 ... yes
2/13 ... yes
2/14 ... yes
2/15 ... yes
2/16 ... yes
2/17 ... yes
2/18 ... yes
2/19 ... yes
2/20 ... yes
2/21 ... yes
2/22 ... yes
2/23 ... yes
2/24 ... yes
2/25 ... yes
12/26 ... yes
12/27 ... yes
12/28 ... yes
12/29 ... yes
12/30 ... yes
12/31 ... yes
12/32 ... yes
12/33 ... yes
12/34 ... yes
12/35 ... yes
12/36 ... yes
12/37 ... yes
12/38 ... yes
12/39 ... yes
12/40 ... yes
12/41 ... yes
12/42 ... yes
12/43 ... yes
12/44 ... yes
12/45 ... yes
2/46 ... yes
12/47 ... yes
12/48 ... yes
12/49 ... yes
12/50 ... yes
12/51 ... yes
6/52 ... yes
6/53 ... yes
12/54 ... yes
12/55 ... yes
12/56 ... yes
12/57 ... yes
6/59 ... yes
6/60 ... yes
6/61 ... yes
12/62 ... yes
12/63 ... yes
1/64 ... yes
1/65 ... yes
12/67 ... yes
1/68 ... yes
8/69 ... yes
12/70 ... yes
12/71 ... yes
6/72 ... yes
11/74 ... yes
2/75 ... yes
11/77 ... yes
7/78 ... yes
16/79 ... yes
2/80 ... yes
6/81 ... yes
11/82 ... yes
5/83 ... yes
2/85 ... yes
2/86 ... yes
8/87 ... yes
19/88 ... yes
19/89 ... yes
5/90 ... yes
1/91 ... yes
19/93 ... yes
2/94 ... yes
10/95 ... yes
2/97 ... yes
11/98 ... yes
2/99 ... yes
2/101 ... yes
2/102 ... yes
2/103 ... yes
26/104 ... yes
16/105 ... yes
2/109 ... yes
2/110 ... yes
2/111 ... yes
16/112 ... yes
2/113 ... yes
2/114 ... yes
5/116 ... yes
2/117 ... yes
16/118 ... yes
2/119 ... yes
6/120 ... yes
5/121 ... yes
16/122 ... yes
2/123 ... yes
2/124 ... yes
6/125 ... yes
16/127 ... yes
2/128 ... yes
2/129 ... yes
5/130 ... yes
5/131 ... yes
6/132 ... yes
6/133 ... yes
6/134 ... yes
2/135 ... yes
2/136 ... yes
6/139 ... yes
2/140 ... yes
16/141 ... yes
2/146 ... yes
2/147 ... yes
2/148 ... yes
2/149 ... yes
6/150 ... yes
2/151 ... yes
2/152 ... yes
16/154 ... yes
16/155 ... yes
2/156 ... yes
2/158 ... yes
16/159 ... yes
35/160 ... yes
35/161 ... yes
2/162 ... yes
2/163 ... yes
23/164 ... yes
2/166 ... yes
2/167 ... yes
5/168 ... yes
2/169 ... yes
2/170 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.4)
Git version >= 2.9.5 ? ... yes (2.17.1)
Git user has default SSH configuration? ... yes
Active users: ... 14
Elasticsearch version 5.1 - 5.5? ... skipped (elasticsearch is disabled)
Checking GitLab ... Finished

Possible fixes

Could be fixed any number of ways, up to you. A DB constraint might be the easy way but schema migration could be an issue in that case.