Merge branch 'jej/backport-authorized-keys-to-ce' into 'master'

Backport authorized_keys

Closes gitlab-ee#3953

See merge request gitlab-org/gitlab-ce!16014

app/helpers/application_settings_helper.rb

@@ -146,6 +146,7 @@ module ApplicationSettingsHelper
       :after_sign_up_text,
       :akismet_api_key,
       :akismet_enabled,
+      :authorized_keys_enabled,
       :auto_devops_enabled,
       :circuitbreaker_access_retries,
       :circuitbreaker_check_interval,

app/models/application_setting.rb

@@ -261,6 +261,7 @@ class ApplicationSetting < ActiveRecord::Base
     {
       after_sign_up_text: nil,
       akismet_enabled: false,
+      authorized_keys_enabled: true, # TODO default to false if the instance is configured to use AuthorizedKeysCommand
       container_registry_token_expire_delay: 5,
       default_artifacts_expire_in: '30 days',
       default_branch_protection: Settings.gitlab['default_branch_protection'],

app/views/admin/application_settings/_form.html.haml

@@ -774,6 +774,22 @@
           installations. Set to 0 to completely disable polling.
           = link_to icon('question-circle'), help_page_path('administration/polling')
 
+  %fieldset
+    %legend Performance optimization
+    .form-group
+      .col-sm-offset-2.col-sm-10
+        .checkbox
+          = f.label :authorized_keys_enabled do
+            = f.check_box :authorized_keys_enabled
+            Write to "authorized_keys" file
+          .help-block
+            By default, we write to the "authorized_keys" file to support Git
+            over SSH without additional configuration. GitLab can be optimized
+            to authenticate SSH keys via the database file. Only uncheck this
+            if you have configured your OpenSSH server to use the
+            AuthorizedKeysCommand. Click on the help icon for more details.
+            = link_to icon('question-circle'), help_page_path('administration/operations/fast_ssh_key_lookup')
+
   %fieldset
     %legend User and IP Rate Limits
     .form-group

changelogs/unreleased/jej-backport-authorized-keys-to-ce.yml

@@ -0,0 +1,5 @@
+---
+title: Backport fast database lookup of SSH authorized_keys from EE
+merge_request: 16014
+author:
+type: added

db/migrate/20160301174731_add_fingerprint_index.rb

@@ -0,0 +1,17 @@
+# rubocop:disable all
+class AddFingerprintIndex < ActiveRecord::Migration
+  disable_ddl_transaction!
+
+  DOWNTIME = false
+
+  # https://gitlab.com/gitlab-org/gitlab-ee/issues/764
+  def change
+    args = [:keys, :fingerprint]
+
+    if Gitlab::Database.postgresql?
+      args << { algorithm: :concurrently }
+    end
+
+    add_index(*args) unless index_exists?(:keys, :fingerprint)
+  end
+end

db/migrate/20170531180233_add_authorized_keys_enabled_to_application_settings.rb

@@ -0,0 +1,19 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddAuthorizedKeysEnabledToApplicationSettings < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default :application_settings, :authorized_keys_enabled, :boolean, default: true, allow_null: false
+  end
+
+  def down
+    remove_column :application_settings, :authorized_keys_enabled
+  end
+end

db/schema.rb

@@ -154,6 +154,7 @@ ActiveRecord::Schema.define(version: 20171230123729) do
     t.integer "gitaly_timeout_default", default: 55, null: false
     t.integer "gitaly_timeout_medium", default: 30, null: false
     t.integer "gitaly_timeout_fast", default: 10, null: false
+    t.boolean "authorized_keys_enabled", default: true, null: false
   end
 
   create_table "audit_events", force: :cascade do |t|

doc/administration/operations/fast_ssh_key_lookup.md

@@ -0,0 +1,192 @@
+# Fast lookup of authorized SSH keys in the database
+
+Regular SSH operations become slow as the number of users grows because OpenSSH
+searches for a key to authorize a user via a linear search. In the worst case,
+such as when the user is not authorized to access GitLab, OpenSSH will scan the
+entire file to search for a key. This can take significant time and disk I/O,
+which will delay users attempting to push or pull to a repository. Making
+matters worse, if users add or remove keys frequently, the operating system may
+not be able to cache the `authorized_keys` file, which causes the disk to be
+accessed repeatedly.
+
+GitLab Shell solves this by providing a way to authorize SSH users via a fast,
+indexed lookup in the GitLab database. This page describes how to enable the fast
+lookup of authorized SSH keys.
+
+> **Warning:** OpenSSH version 6.9+ is required because
+`AuthorizedKeysCommand` must be able to accept a fingerprint. These
+instructions will break installations using older versions of OpenSSH, such as
+those included with CentOS 6 as of September 2017. If you want to use this
+feature for CentOS 6, follow [the instructions on how to build and install a custom OpenSSH package](#compiling-a-custom-version-of-openssh-for-centos-6) before continuing.
+
+## Setting up fast lookup via GitLab Shell
+
+GitLab Shell provides a way to authorize SSH users via a fast, indexed lookup
+to the GitLab database. GitLab Shell uses the fingerprint of the SSH key to
+check whether the user is authorized to access GitLab.
+
+Create the directory `/opt/gitlab-shell` first:
+
+```bash
+sudo mkdir -p /opt/gitlab-shell
+```
+
+Create this file at `/opt/gitlab-shell/authorized_keys`:
+
+```
+#!/bin/bash
+
+if [[ "$1" == "git" ]]; then
+  /opt/gitlab/embedded/service/gitlab-shell/bin/authorized_keys $2
+fi
+```
+
+Set appropriate ownership and permissions:
+
+```
+sudo chown root:git /opt/gitlab-shell/authorized_keys
+sudo chmod 0650 /opt/gitlab-shell/authorized_keys
+```
+
+Add the following to `/etc/ssh/sshd_config` or to `/assets/sshd_config` if you
+are using Omnibus Docker:
+
+```
+AuthorizedKeysCommand /opt/gitlab-shell/authorized_keys %u %k
+AuthorizedKeysCommandUser git
+```
+
+Reload OpenSSH:
+
+```bash
+# Debian or Ubuntu installations
+sudo service ssh reload
+
+# CentOS installations
+sudo service sshd reload
+```
+
+Confirm that SSH is working by removing your user's SSH key in the UI, adding a
+new one, and attempting to pull a repo.
+
+> **Warning:** Do not disable writes until SSH is confirmed to be working
+perfectly because the file will quickly become out-of-date.
+
+In the case of lookup failures (which are not uncommon), the `authorized_keys`
+file will still be scanned. So git SSH performance will still be slow for many
+users as long as a large file exists.
+
+You can disable any more writes to the `authorized_keys` file by unchecking
+`Write to "authorized_keys" file` in the Application Settings of your GitLab
+installation.
+
+![Write to authorized keys setting](img/write_to_authorized_keys_setting.png)
+
+Again, confirm that SSH is working by removing your user's SSH key in the UI,
+adding a new one, and attempting to pull a repo.
+
+Then you can backup and delete your `authorized_keys` file for best performance.
+
+## How to go back to using the `authorized_keys` file
+
+This is a brief overview. Please refer to the above instructions for more context.
+
+1. [Rebuild the `authorized_keys` file](../raketasks/maintenance.md#rebuild-authorized_keys-file)
+1. Enable writes to the `authorized_keys` file in Application Settings
+1. Remove the `AuthorizedKeysCommand` lines from `/etc/ssh/sshd_config` or from `/assets/sshd_config` if you are using Omnibus Docker.
+1. Reload sshd: `sudo service sshd reload`
+1. Remove the `/opt/gitlab-shell/authorized_keys` file
+
+## Compiling a custom version of OpenSSH for CentOS 6
+
+Building a custom version of OpenSSH is not necessary for Ubuntu 16.04 users,
+since Ubuntu 16.04 ships with OpenSSH 7.2.
+
+It is also unnecessary for CentOS 7.4 users, as that version ships with
+OpenSSH 7.4. If you are using CentOS 7.0 - 7.3, we strongly recommend that you
+upgrade to CentOS 7.4 instead of following this procedure. This should be as
+simple as running `yum update`.
+
+CentOS 6 users must build their own OpenSSH package to enable SSH lookups via
+the database. The following instructions can be used to build OpenSSH 7.5:
+
+1. First, download the package and install the required packages:
+
+    ```
+    sudo su -
+    cd /tmp
+    curl --remote-name https://mirrors.evowise.com/pub/OpenBSD/OpenSSH/portable/openssh-7.5p1.tar.gz
+    tar xzvf openssh-7.5p1.tar.gz
+    yum install rpm-build gcc make wget openssl-devel krb5-devel pam-devel libX11-devel xmkmf libXt-devel
+    ```
+
+3. Prepare the build by copying files to the right place:
+
+    ```
+    mkdir -p /root/rpmbuild/{SOURCES,SPECS}
+    cp ./openssh-7.5p1/contrib/redhat/openssh.spec /root/rpmbuild/SPECS/
+    cp openssh-7.5p1.tar.gz /root/rpmbuild/SOURCES/
+    cd /root/rpmbuild/SPECS
+    ```
+
+3. Next, set the spec settings properly:
+
+    ```
+    sed -i -e "s/%define no_gnome_askpass 0/%define no_gnome_askpass 1/g" openssh.spec
+    sed -i -e "s/%define no_x11_askpass 0/%define no_x11_askpass 1/g" openssh.spec
+    sed -i -e "s/BuildPreReq/BuildRequires/g" openssh.spec
+    ```
+
+3. Build the RPMs:
+
+    ```
+    rpmbuild -bb openssh.spec
+    ```
+
+4. Ensure the RPMs were built:
+
+    ```
+    ls -al /root/rpmbuild/RPMS/x86_64/
+    ```
+
+    You should see something as the following:
+
+    ```
+    total 1324
+    drwxr-xr-x. 2 root root   4096 Jun 20 19:37 .
+    drwxr-xr-x. 3 root root     19 Jun 20 19:37 ..
+    -rw-r--r--. 1 root root 470828 Jun 20 19:37 openssh-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root 490716 Jun 20 19:37 openssh-clients-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root  17020 Jun 20 19:37 openssh-debuginfo-7.5p1-1.x86_64.rpm
+    -rw-r--r--. 1 root root 367516 Jun 20 19:37 openssh-server-7.5p1-1.x86_64.rpm
+    ```
+
+5. Install the packages. OpenSSH packages will replace `/etc/pam.d/sshd`
+   with its own version, which may prevent users from logging in, so be sure
+   that the file is backed up and restored after installation:
+
+    ```
+    timestamp=$(date +%s)
+    cp /etc/pam.d/sshd pam-ssh-conf-$timestamp
+    rpm -Uvh /root/rpmbuild/RPMS/x86_64/*.rpm
+    yes | cp pam-ssh-conf-$timestamp /etc/pam.d/sshd
+    ```
+
+6. Verify the installed version. In another window, attempt to login to the server:
+
+    ```
+    ssh -v <your-centos-machine>
+    ```
+
+    You should see a line that reads: "debug1: Remote protocol version 2.0, remote software version OpenSSH_7.5"
+
+    If not, you may need to restart sshd (e.g. `systemctl restart sshd.service`).
+
+7.  *IMPORTANT!* Open a new SSH session to your server before exiting to make
+    sure everything is working! If you need to downgrade, simple install the
+    older package:
+
+    ```
+    # Only run this if you run into a problem logging in
+    yum downgrade openssh-server openssh openssh-clients
+    ```

doc/administration/operations/index.md

@@ -13,4 +13,5 @@ by GitLab to another file system or another server.
 that to prioritize important jobs.
 - [Sidekiq MemoryKiller](sidekiq_memory_killer.md): Configure Sidekiq MemoryKiller
 to restart Sidekiq.
-- [Unicorn](unicorn.md): Understand Unicorn and unicorn-worker-killer.
+- [Unicorn](unicorn.md): Understand Unicorn and unicorn-worker-killer.
+- [Speed up SSH operations](fast_ssh_key_lookup.md): Authorize SSH users via a fast, indexed lookup to the GitLab database.

doc/administration/operations/speed_up_ssh.md

@@ -0,0 +1 @@
+This document was moved to [another location](fast_ssh_key_lookup.md).

lib/api/internal.rb

@@ -81,6 +81,18 @@ module API
         merge_request_urls
       end
 
+      #
+      # Get a ssh key using the fingerprint
+      #
+      get "/authorized_keys" do
+        fingerprint = params.fetch(:fingerprint) do
+          Gitlab::InsecureKeyFingerprint.new(params.fetch(:key)).fingerprint
+        end
+        key = Key.find_by(fingerprint: fingerprint)
+        not_found!("Key") if key.nil?
+        present key, with: Entities::SSHKey
+      end
+
       #
       # Discover user by ssh key or user id
       #

lib/gitlab/insecure_key_fingerprint.rb

@@ -0,0 +1,23 @@
+module Gitlab
+  #
+  # Calculates the fingerprint of a given key without using
+  # openssh key validations. For this reason, only use
+  # for calculating the fingerprint to find the key with it.
+  #
+  # DO NOT use it for checking the validity of a ssh key.
+  #
+  class InsecureKeyFingerprint
+    attr_accessor :key
+
+    #
+    # Gets the base64 encoded string representing a rsa or dsa key
+    #
+    def initialize(key_base64)
+      @key = key_base64
+    end
+
+    def fingerprint
+      OpenSSL::Digest::MD5.hexdigest(Base64.decode64(@key)).scan(/../).join(':')
+    end
+  end
+end

lib/gitlab/shell.rb

@@ -183,6 +183,8 @@ module Gitlab
     #   add_key("key-42", "sha-rsa ...")
     #
     def add_key(key_id, key_content)
+      return unless self.authorized_keys_enabled?
+
       gitlab_shell_fast_execute([gitlab_shell_keys_path,
                                  'add-key', key_id, self.class.strip_key(key_content)])
     end
@@ -192,6 +194,8 @@ module Gitlab
     # Ex.
     #   batch_add_keys { |adder| adder.add_key("key-42", "sha-rsa ...") }
     def batch_add_keys(&block)
+      return unless self.authorized_keys_enabled?
+
       IO.popen(%W(#{gitlab_shell_path}/bin/gitlab-keys batch-add-keys), 'w') do |io|
         yield(KeyAdder.new(io))
       end
@@ -202,10 +206,11 @@ module Gitlab
     # Ex.
     #   remove_key("key-342", "sha-rsa ...")
     #
-    def remove_key(key_id, key_content)
+    def remove_key(key_id, key_content = nil)
+      return unless self.authorized_keys_enabled?
+
       args = [gitlab_shell_keys_path, 'rm-key', key_id]
       args << key_content if key_content
-
       gitlab_shell_fast_execute(args)
     end
 
@@ -215,9 +220,62 @@ module Gitlab
     #   remove_all_keys
     #
     def remove_all_keys
+      return unless self.authorized_keys_enabled?
+
       gitlab_shell_fast_execute([gitlab_shell_keys_path, 'clear'])
     end
 
+    # Remove ssh keys from gitlab shell that are not in the DB
+    #
+    # Ex.
+    #   remove_keys_not_found_in_db
+    #
+    def remove_keys_not_found_in_db
+      return unless self.authorized_keys_enabled?
+
+      Rails.logger.info("Removing keys not found in DB")
+
+      batch_read_key_ids do |ids_in_file|
+        ids_in_file.uniq!
+        keys_in_db = Key.where(id: ids_in_file)
+
+        next unless ids_in_file.size > keys_in_db.count # optimization
+
+        ids_to_remove = ids_in_file - keys_in_db.pluck(:id)
+        ids_to_remove.each do |id|
+          Rails.logger.info("Removing key-#{id} not found in DB")
+          remove_key("key-#{id}")
+        end
+      end
+    end
+
+    # Iterate over all ssh key IDs from gitlab shell, in batches
+    #
+    # Ex.
+    #   batch_read_key_ids { |batch| keys = Key.where(id: batch) }
+    #
+    def batch_read_key_ids(batch_size: 100, &block)
+      return unless self.authorized_keys_enabled?
+
+      list_key_ids do |key_id_stream|
+        key_id_stream.lazy.each_slice(batch_size) do |lines|
+          key_ids = lines.map { |l| l.chomp.to_i }
+          yield(key_ids)
+        end
+      end
+    end
+
+    # Stream all ssh key IDs from gitlab shell, separated by newlines
+    #
+    # Ex.
+    #   list_key_ids
+    #
+    def list_key_ids(&block)
+      return unless self.authorized_keys_enabled?
+
+      IO.popen(%W(#{gitlab_shell_path}/bin/gitlab-keys list-key-ids), &block)
+    end
+
     # Add empty directory for storing repositories
     #
     # Ex.
@@ -333,6 +391,14 @@ module Gitlab
       File.join(gitlab_shell_path, 'bin', 'gitlab-keys')
     end
 
+    def authorized_keys_enabled?
+      # Return true if nil to ensure the authorized_keys methods work while
+      # fixing the authorized_keys file during migration.
+      return true if Gitlab::CurrentSettings.current_application_settings.authorized_keys_enabled.nil?
+
+      Gitlab::CurrentSettings.current_application_settings.authorized_keys_enabled
+    end
+
     private
 
     def gitlab_projects(shard_path, disk_path)

spec/lib/gitlab/insecure_key_fingerprint_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+
+describe Gitlab::InsecureKeyFingerprint do
+  let(:key) do
+    'ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAIEAiPWx6WM4lhHNedGfBpPJNPpZ7yKu+dnn' \
+    '1SJejgt4596k6YjzGGphH2TUxwKzxcKDKKezwkpfnxPkSMkuEspGRt/aZZ9wa++Oi7Qk' \
+    'r8prgHc4soW6NUlfDzpvZK2H5E7eQaSeP3SAwGmQKUFHCddNaP0L+hM7zhFNzjFvpaMg' \
+    'Jw0='
+  end
+
+  let(:fingerprint) { "3f:a2:ee:de:b5:de:53:c3:aa:2f:9c:45:24:4c:47:7b" }
+
+  describe "#fingerprint" do
+    it "generates the key's fingerprint" do
+      expect(described_class.new(key.split[1]).fingerprint).to eq(fingerprint)
+    end
+  end
+end

spec/lib/gitlab/shell_spec.rb

@@ -52,6 +52,311 @@ describe Gitlab::Shell do
     end
   end
 
+  describe '#add_key' do
+    context 'when authorized_keys_enabled is true' do
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'add-key', 'key-123', 'ssh-rsa foobar']
+        )
+
+        gitlab_shell.add_key('key-123', 'ssh-rsa foobar trailing garbage')
+      end
+    end
+
+    context 'when authorized_keys_enabled is false' do
+      before do
+        stub_application_setting(authorized_keys_enabled: false)
+      end
+
+      it 'does nothing' do
+        expect(gitlab_shell).not_to receive(:gitlab_shell_fast_execute)
+
+        gitlab_shell.add_key('key-123', 'ssh-rsa foobar trailing garbage')
+      end
+    end
+
+    context 'when authorized_keys_enabled is nil' do
+      before do
+        stub_application_setting(authorized_keys_enabled: nil)
+      end
+
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'add-key', 'key-123', 'ssh-rsa foobar']
+        )
+
+        gitlab_shell.add_key('key-123', 'ssh-rsa foobar trailing garbage')
+      end
+    end
+  end
+
+  describe '#batch_add_keys' do
+    context 'when authorized_keys_enabled is true' do
+      it 'instantiates KeyAdder' do
+        expect_any_instance_of(Gitlab::Shell::KeyAdder).to receive(:add_key).with('key-123', 'ssh-rsa foobar')
+
+        gitlab_shell.batch_add_keys do |adder|
+          adder.add_key('key-123', 'ssh-rsa foobar')
+        end
+      end
+    end
+
+    context 'when authorized_keys_enabled is false' do
+      before do
+        stub_application_setting(authorized_keys_enabled: false)
+      end
+
+      it 'does nothing' do
+        expect_any_instance_of(Gitlab::Shell::KeyAdder).not_to receive(:add_key)
+
+        gitlab_shell.batch_add_keys do |adder|
+          adder.add_key('key-123', 'ssh-rsa foobar')
+        end
+      end
+    end
+
+    context 'when authorized_keys_enabled is nil' do
+      before do
+        stub_application_setting(authorized_keys_enabled: nil)
+      end
+
+      it 'instantiates KeyAdder' do
+        expect_any_instance_of(Gitlab::Shell::KeyAdder).to receive(:add_key).with('key-123', 'ssh-rsa foobar')
+
+        gitlab_shell.batch_add_keys do |adder|
+          adder.add_key('key-123', 'ssh-rsa foobar')
+        end
+      end
+    end
+  end
+
+  describe '#remove_key' do
+    context 'when authorized_keys_enabled is true' do
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'rm-key', 'key-123', 'ssh-rsa foobar']
+        )
+
+        gitlab_shell.remove_key('key-123', 'ssh-rsa foobar')
+      end
+    end
+
+    context 'when authorized_keys_enabled is false' do
+      before do
+        stub_application_setting(authorized_keys_enabled: false)
+      end
+
+      it 'does nothing' do
+        expect(gitlab_shell).not_to receive(:gitlab_shell_fast_execute)
+
+        gitlab_shell.remove_key('key-123', 'ssh-rsa foobar')
+      end
+    end
+
+    context 'when authorized_keys_enabled is nil' do
+      before do
+        stub_application_setting(authorized_keys_enabled: nil)
+      end
+
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'rm-key', 'key-123', 'ssh-rsa foobar']
+        )
+
+        gitlab_shell.remove_key('key-123', 'ssh-rsa foobar')
+      end
+    end
+
+    context 'when key content is not given' do
+      it 'calls rm-key with only one argument' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'rm-key', 'key-123']
+        )
+
+        gitlab_shell.remove_key('key-123')
+      end
+    end
+  end
+
+  describe '#remove_all_keys' do
+    context 'when authorized_keys_enabled is true' do
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with([:gitlab_shell_keys_path, 'clear'])
+
+        gitlab_shell.remove_all_keys
+      end
+    end
+
+    context 'when authorized_keys_enabled is false' do
+      before do
+        stub_application_setting(authorized_keys_enabled: false)
+      end
+
+      it 'does nothing' do
+        expect(gitlab_shell).not_to receive(:gitlab_shell_fast_execute)
+
+        gitlab_shell.remove_all_keys
+      end
+    end
+
+    context 'when authorized_keys_enabled is nil' do
+      before do
+        stub_application_setting(authorized_keys_enabled: nil)
+      end
+
+      it 'removes trailing garbage' do
+        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
+        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
+          [:gitlab_shell_keys_path, 'clear']
+        )
+
+        gitlab_shell.remove_all_keys
+      end
+    end
+  end
+
+  describe '#remove_keys_not_found_in_db' do
+    context 'when keys are in the file that are not in the DB' do
+      before do
+        gitlab_shell.remove_all_keys
+        gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+        gitlab_shell.add_key('key-9876', 'ssh-rsa ASDFASDF')
+        @another_key = create(:key) # this one IS in the DB
+      end
+
+      it 'removes the keys' do
+        expect(find_in_authorized_keys_file(1234)).to be_truthy
+        expect(find_in_authorized_keys_file(9876)).to be_truthy
+        expect(find_in_authorized_keys_file(@another_key.id)).to be_truthy
+        gitlab_shell.remove_keys_not_found_in_db
+        expect(find_in_authorized_keys_file(1234)).to be_falsey
+        expect(find_in_authorized_keys_file(9876)).to be_falsey
+        expect(find_in_authorized_keys_file(@another_key.id)).to be_truthy
+      end
+    end
+
+    context 'when keys there are duplicate keys in the file that are not in the DB' do
+      before do
+        gitlab_shell.remove_all_keys
+        gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+        gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+      end
+
+      it 'removes the keys' do
+        expect(find_in_authorized_keys_file(1234)).to be_truthy
+        gitlab_shell.remove_keys_not_found_in_db
+        expect(find_in_authorized_keys_file(1234)).to be_falsey
+      end
+
+      it 'does not run remove more than once per key (in a batch)' do
+        expect(gitlab_shell).to receive(:remove_key).with('key-1234').once
+        gitlab_shell.remove_keys_not_found_in_db
+      end
+    end
+
+    context 'when keys there are duplicate keys in the file that ARE in the DB' do
+      before do
+        gitlab_shell.remove_all_keys
+        @key = create(:key)
+        gitlab_shell.add_key(@key.shell_id, @key.key)
+      end
+
+      it 'does not remove the key' do
+        gitlab_shell.remove_keys_not_found_in_db
+        expect(find_in_authorized_keys_file(@key.id)).to be_truthy
+      end
+
+      it 'does not need to run a SELECT query for that batch, on account of that key' do
+        expect_any_instance_of(ActiveRecord::Relation).not_to receive(:pluck)
+        gitlab_shell.remove_keys_not_found_in_db
+      end
+    end
+
+    unless ENV['CI'] # Skip in CI, it takes 1 minute
+      context 'when the first batch can be skipped, but the next batch has keys that are not in the DB' do
+        before do
+          gitlab_shell.remove_all_keys
+          100.times { |i| create(:key) } # first batch is all in the DB
+          gitlab_shell.add_key('key-1234', 'ssh-rsa ASDFASDF')
+        end
+
+        it 'removes the keys not in the DB' do
+          expect(find_in_authorized_keys_file(1234)).to be_truthy
+          gitlab_shell.remove_keys_not_found_in_db
+          expect(find_in_authorized_keys_file(1234)).to be_falsey
+        end
+      end
+    end
+  end
+
+  describe '#batch_read_key_ids' do
+    context 'when there are keys in the authorized_keys file' do
+      before do
+        gitlab_shell.remove_all_keys
+        (1..4).each do |i|
+          gitlab_shell.add_key("key-#{i}", "ssh-rsa ASDFASDF#{i}")
+        end
+      end
+
+      it 'iterates over the key IDs in the file, in batches' do
+        loop_count = 0
+        first_batch = [1, 2]
+        second_batch = [3, 4]
+
+        gitlab_shell.batch_read_key_ids(batch_size: 2) do |batch|
+          expected = (loop_count == 0 ? first_batch : second_batch)
+          expect(batch).to eq(expected)
+          loop_count += 1
+        end
+      end
+    end
+  end
+
+  describe '#list_key_ids' do
+    context 'when there are keys in the authorized_keys file' do
+      before do
+        gitlab_shell.remove_all_keys
+        (1..4).each do |i|
+          gitlab_shell.add_key("key-#{i}", "ssh-rsa ASDFASDF#{i}")
+        end
+      end
+
+      it 'outputs the key IDs in the file, separated by newlines' do
+        ids = []
+        gitlab_shell.list_key_ids do |io|
+          io.each do |line|
+            ids << line
+          end
+        end
+
+        expect(ids).to eq(%W{1\n 2\n 3\n 4\n})
+      end
+    end
+
+    context 'when there are no keys in the authorized_keys file' do
+      before do
+        gitlab_shell.remove_all_keys
+      end
+
+      it 'outputs nothing, not even an empty string' do
+        ids = []
+        gitlab_shell.list_key_ids do |io|
+          io.each do |line|
+            ids << line
+          end
+        end
+
+        expect(ids).to eq([])
+      end
+    end
+  end
+
   describe Gitlab::Shell::KeyAdder do
     describe '#add_key' do
       it 'removes trailing garbage' do
@@ -97,17 +402,6 @@ describe Gitlab::Shell do
       allow(Gitlab.config.gitlab_shell).to receive(:git_timeout).and_return(800)
     end
 
-    describe '#add_key' do
-      it 'removes trailing garbage' do
-        allow(gitlab_shell).to receive(:gitlab_shell_keys_path).and_return(:gitlab_shell_keys_path)
-        expect(gitlab_shell).to receive(:gitlab_shell_fast_execute).with(
-          [:gitlab_shell_keys_path, 'add-key', 'key-123', 'ssh-rsa foobar']
-        )
-
-        gitlab_shell.add_key('key-123', 'ssh-rsa foobar trailing garbage')
-      end
-    end
-
     describe '#add_repository' do
       shared_examples '#add_repository' do
         let(:repository_storage) { 'default' }
@@ -412,4 +706,12 @@ describe Gitlab::Shell do
       end
     end
   end
+
+  def find_in_authorized_keys_file(key_id)
+    gitlab_shell.batch_read_key_ids do |ids|
+      return true if ids.include?(key_id)
+    end
+
+    false
+  end
 end

spec/requests/api/internal_spec.rb

@@ -192,6 +192,54 @@ describe API::Internal do
     end
   end
 
+  describe "GET /internal/authorized_keys" do
+    context "using an existing key's fingerprint" do
+      it "finds the key" do
+        get(api('/internal/authorized_keys'), fingerprint: key.fingerprint, secret_token: secret_token)
+
+        expect(response.status).to eq(200)
+        expect(json_response["key"]).to eq(key.key)
+      end
+    end
+
+    context "non existing key's fingerprint" do
+      it "returns 404" do
+        get(api('/internal/authorized_keys'), fingerprint: "no:t-:va:li:d0", secret_token: secret_token)
+
+        expect(response.status).to eq(404)
+      end
+    end
+
+    context "using a partial fingerprint" do
+      it "returns 404" do
+        get(api('/internal/authorized_keys'), fingerprint: "#{key.fingerprint[0..5]}%", secret_token: secret_token)
+
+        expect(response.status).to eq(404)
+      end
+    end
+
+    context "sending the key" do
+      it "finds the key" do
+        get(api('/internal/authorized_keys'), key: key.key.split[1], secret_token: secret_token)
+
+        expect(response.status).to eq(200)
+        expect(json_response["key"]).to eq(key.key)
+      end
+
+      it "returns 404 with a partial key" do
+        get(api('/internal/authorized_keys'), key: key.key.split[1][0...-3], secret_token: secret_token)
+
+        expect(response.status).to eq(404)
+      end
+
+      it "returns 404 with an not valid base64 string" do
+        get(api('/internal/authorized_keys'), key: "whatever!", secret_token: secret_token)
+
+        expect(response.status).to eq(404)
+      end
+    end
+  end
+
   describe "POST /internal/allowed", :clean_gitlab_redis_shared_state do
     context "access granted" do
       around do |example|

spec/workers/gitlab_shell_worker_spec.rb

@@ -0,0 +1,12 @@
+require 'spec_helper'
+
+describe GitlabShellWorker do
+  let(:worker) { described_class.new }
+
+  describe '#perform with add_key' do
+    it 'calls add_key on Gitlab::Shell' do
+      expect_any_instance_of(Gitlab::Shell).to receive(:add_key).with('foo', 'bar')
+      worker.perform(:add_key, 'foo', 'bar')
+    end
+  end
+end