Add limit for wiki page content size

This adds a new validation to restrict the maximum size of a wiki page,
which is only enforced when the content is updated, and only when using
the GitLab UI or API (not for Git pushes yet).

The default limit is 50MB, and can be changed through the Rails console
or the API.

app/helpers/application_settings_helper.rb

@@ -327,7 +327,8 @@ module ApplicationSettingsHelper
       :project_download_export_limit,
       :group_import_limit,
       :group_export_limit,
-      :group_download_export_limit
+      :group_download_export_limit,
+      :wiki_page_max_content_bytes
     ]
   end
 

app/models/application_setting.rb

@@ -272,6 +272,7 @@ class ApplicationSetting < ApplicationRecord
             numericality: { greater_than_or_equal_to: 0 }
 
   validates :snippet_size_limit, numericality: { only_integer: true, greater_than: 0 }
+  validates :wiki_page_max_content_bytes, numericality: { only_integer: true, greater_than: 0 }
 
   validates :email_restrictions, untrusted_regexp: true
 

app/models/application_setting_implementation.rb

@@ -164,7 +164,8 @@ module ApplicationSettingImplementation
         project_download_export_limit: 1,
         group_import_limit: 6,
         group_export_limit: 6,
-        group_download_export_limit: 1
+        group_download_export_limit: 1,
+        wiki_page_max_content_bytes: 50.megabytes
       }
     end
 

app/models/wiki_page.rb

@@ -65,6 +65,7 @@ class WikiPage
   validates :title, presence: true
   validates :content, presence: true
   validate :validate_path_limits, if: :title_changed?
+  validate :validate_content_size_limit, if: :content_changed?
 
   # The GitLab Wiki instance.
   attr_reader :wiki
@@ -282,6 +283,10 @@ class WikiPage
     end
   end
 
+  def content_changed?
+    attributes[:content] != page&.text_data
+  end
+
   # Updates the current @attributes hash by merging a hash of params
   def update_attributes(attrs)
     attrs[:title] = process_title(attrs[:title]) if attrs[:title].present?
@@ -391,4 +396,15 @@ class WikiPage
       })
     end
   end
+
+  def validate_content_size_limit
+    current_value = raw_content.to_s.bytesize
+    max_size = Gitlab::CurrentSettings.wiki_page_max_content_bytes
+    return if current_value <= max_size
+
+    errors.add(:content, _('is too long (%{current_value}). The maximum size is %{max_size}.') % {
+      current_value: ActiveSupport::NumberHelper.number_to_human_size(current_value),
+      max_size: ActiveSupport::NumberHelper.number_to_human_size(max_size)
+    })
+  end
 end

changelogs/unreleased/31176-wiki-page-size-validation.yml

+---
+title: Add limit for wiki page content size
+merge_request: 36729
+author:
+type: performance

db/migrate/20200713141854_add_wiki_page_max_content_bytes_to_application_settings.rb

+# frozen_string_literal: true
+
+class AddWikiPageMaxContentBytesToApplicationSettings < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def change
+    add_column :application_settings, :wiki_page_max_content_bytes, :bigint, default: 50.megabytes, null: false
+  end
+end

db/structure.sql

@@ -9172,6 +9172,7 @@ CREATE TABLE public.application_settings (
     group_download_export_limit integer DEFAULT 1 NOT NULL,
     maintenance_mode boolean DEFAULT false NOT NULL,
     maintenance_mode_message text,
+    wiki_page_max_content_bytes bigint DEFAULT 52428800 NOT NULL,
     CONSTRAINT check_51700b31b5 CHECK ((char_length(default_branch_name) <= 255)),
     CONSTRAINT check_9c6c447a13 CHECK ((char_length(maintenance_mode_message) <= 255)),
     CONSTRAINT check_d03919528d CHECK ((char_length(container_registry_vendor) <= 255)),
@@ -23860,6 +23861,7 @@ COPY "schema_migrations" (version) FROM STDIN;
 20200712084655
 20200712235622
 20200713071042
+20200713141854
 20200713152443
 20200716044023
 20200716120419

doc/administration/index.md

@@ -163,7 +163,11 @@ Learn how to install, configure, update, and maintain your GitLab instance.
 
 ## Snippet settings
 
-- [Setting snippet content size limit](snippets/index.md): Set a maximum size limit for snippets' content.
+- [Setting snippet content size limit](snippets/index.md): Set a maximum content size limit for snippets.
+
+## Wiki settings
+
+- [Setting wiki page content size limit](wikis/index.md): Set a maximum content size limit for wiki pages.
 
 ## Git configuration options
 

doc/administration/instance_limits.md

@@ -315,6 +315,7 @@ Set the limit to `0` to disable it.
 
 ## Wiki limits
 
+- [Wiki page content size limit](wikis/index.md#wiki-page-content-size-limit).
 - [Length restrictions for file and directory names](../user/project/wiki/index.md#length-restrictions-for-file-and-directory-names).
 
 ## Snippets limits

doc/administration/snippets/index.md

 ---
 type: reference, howto
+stage: Create
+group: Editor
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 ---
 
 # Snippets settings **(CORE ONLY)**
@@ -10,15 +13,15 @@ Adjust the snippets' settings of your GitLab instance.
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/31133) in GitLab 12.6.
 
-You can set a content size max limit in snippets. This limit can prevent
-abuses of the feature. The default content size limit is **52428800 Bytes** (50MB).
+You can set a maximum content size limit for snippets. This limit can prevent
+abuse of the feature. The default value is **52428800 Bytes** (50 MB).
 
 ### How does it work?
 
-The content size limit will be applied when a snippet is created or
-updated. Nevertheless, in order not to break any existing snippet,
-the limit will only be enforced in stored snippets when the content
-is updated.
+The content size limit will be applied when a snippet is created or updated.
+
+In order not to break any existing snippets, the limit doesn't have any
+effect on them until a snippet is edited again and the content changes.
 
 ### Snippets size limit configuration
 
@@ -27,7 +30,7 @@ In order to configure this setting, use either the Rails console
 or the [Application settings API](../../api/settings.md).
 
 NOTE: **IMPORTANT:**
-The value of the limit **must** be in Bytes.
+The value of the limit **must** be in bytes.
 
 #### Through the Rails console
 

doc/administration/wikis/index.md

+---
+type: reference, howto
+stage: Create
+group: Knowledge
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
+# Wiki settings **(CORE ONLY)**
+
+Adjust the wiki settings of your GitLab instance.
+
+## Wiki page content size limit
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/31176) in GitLab 13.2.
+
+You can set a maximum content size limit for wiki pages. This limit can prevent
+abuse of the feature. The default value is **52428800 Bytes** (50 MB).
+
+### How does it work?
+
+The content size limit will be applied when a wiki page is created or updated
+through the GitLab UI or API. Local changes pushed via Git will not be validated.
+
+In order not to break any existing wiki pages, the limit doesn't have any
+effect on them until a wiki page is edited again and the content changes.
+
+### Wiki page content size limit configuration
+
+This setting is not available through the [Admin Area settings](../../user/admin_area/settings/index.md).
+In order to configure this setting, use either the Rails console
+or the [Application settings API](../../api/settings.md).
+
+NOTE: **IMPORTANT:**
+The value of the limit **must** be in bytes.
+
+#### Through the Rails console
+
+The steps to configure this setting through the Rails console are:
+
+1. Start the Rails console:
+
+   ```shell
+   # For Omnibus installations
+   sudo gitlab-rails console
+
+   # For installations from source
+   sudo -u git -H bundle exec rails console -e production
+   ```
+
+1. Update the wiki page maximum content size:
+
+   ```ruby
+   ApplicationSetting.first.update!(wiki_page_max_content_bytes: 50.megabytes)
+   ```
+
+To retrieve the current value, start the Rails console and run:
+
+  ```ruby
+  Gitlab::CurrentSettings.wiki_page_max_content_bytes
+  ```
+
+#### Through the API
+
+The process to set the wiki page size limit through the Application Settings API is
+exactly the same as you would do to [update any other setting](../../api/settings.md#change-application-settings).
+
+```shell
+curl --request PUT --header "PRIVATE-TOKEN: <your_access_token>" https://gitlab.example.com/api/v4/application/settings?wiki_page_max_content_bytes=52428800
+```
+
+You can also use the API to [retrieve the current value](../../api/settings.md#get-current-application-settings).
+
+```shell
+curl --header "PRIVATE-TOKEN: <your_access_token>" https://gitlab.example.com/api/v4/application/settings
+```

doc/api/settings.md

@@ -71,8 +71,10 @@ Example response:
    "asset_proxy_url": "https://assets.example.com",
    "asset_proxy_whitelist": ["example.com", "*.example.com", "your-instance.com"],
    "npm_package_requests_forwarding": true,
+   "snippet_size_limit": 52428800,
    "issues_create_limit": 300,
-   "raw_blob_request_limit": 300
+   "raw_blob_request_limit": 300,
+   "wiki_page_max_content_bytes": 52428800
 }
 ```
 
@@ -161,8 +163,10 @@ Example response:
   "allow_local_requests_from_web_hooks_and_services": true,
   "allow_local_requests_from_system_hooks": false,
   "npm_package_requests_forwarding": true,
+  "snippet_size_limit": 52428800,
   "issues_create_limit": 300,
-  "raw_blob_request_limit": 300
+  "raw_blob_request_limit": 300,
+  "wiki_page_max_content_bytes": 52428800
 }
 ```
 
@@ -369,3 +373,4 @@ are listed in the descriptions of the relevant settings.
 | `snippet_size_limit`                     | integer          | no                                   | Max snippet content size in **bytes**. Default: 52428800 Bytes (50MB).|
 | `issues_create_limit`                    | integer          | no                                   | Max number of issue creation requests per minute per user. Default: 300. To disable throttling set to 0.|
 | `raw_blob_request_limit`                 | integer          | no                                   | Max number of requests per minute for each raw path. Default: 300. To disable throttling set to 0.|
+| `wiki_page_max_content_bytes`            | integer          | no                                   | Max wiki page content size in **bytes**. Default: 52428800 Bytes (50MB).|

spec/models/application_setting_spec.rb

@@ -72,6 +72,7 @@ RSpec.describe ApplicationSetting do
     it { is_expected.not_to allow_value(nil).for(:push_event_activities_limit) }
 
     it { is_expected.to validate_numericality_of(:snippet_size_limit).only_integer.is_greater_than(0) }
+    it { is_expected.to validate_numericality_of(:wiki_page_max_content_bytes).only_integer.is_greater_than(0) }
     it { is_expected.to validate_presence_of(:max_artifacts_size) }
     it { is_expected.to validate_numericality_of(:max_artifacts_size).only_integer.is_greater_than(0) }
     it { is_expected.to validate_presence_of(:max_pages_size) }

spec/models/wiki_page_spec.rb

@@ -267,6 +267,53 @@ RSpec.describe WikiPage do
       expect(subject.errors.keys).to contain_exactly(:content)
     end
 
+    describe 'content size validation' do
+      let(:limit) { 10 }
+
+      before do
+        stub_application_setting(wiki_page_max_content_bytes: limit)
+      end
+
+      it 'accepts content below the limit' do
+        subject.attributes[:content] = 'a' * 10
+
+        expect(subject).to be_valid
+      end
+
+      it 'rejects content exceeding the limit' do
+        subject.attributes[:content] = 'a' * 11
+
+        expect(subject).not_to be_valid
+        expect(subject.errors.messages).to eq(
+          content: ['is too long (11 Bytes). The maximum size is 10 Bytes.']
+        )
+      end
+
+      it 'counts content size in bytes rather than characters' do
+        subject.attributes[:content] = '💩💩💩'
+
+        expect(subject).not_to be_valid
+        expect(subject.errors.messages).to eq(
+          content: ['is too long (12 Bytes). The maximum size is 10 Bytes.']
+        )
+      end
+
+      context 'with an existing page exceeding the limit' do
+        let(:limit) { existing_page.content.bytesize - 1 }
+
+        it 'accepts content when it has not changed' do
+          expect(existing_page).to be_valid
+        end
+
+        it 'rejects content when it has changed' do
+          existing_page.attributes[:content] = 'a' * (limit + 1)
+
+          expect(existing_page).not_to be_valid
+          expect(existing_page.errors.keys).to contain_exactly(:content)
+        end
+      end
+    end
+
     describe '#validate_path_limits' do
       let(:max_title) { Gitlab::WikiPages::MAX_TITLE_BYTES }
       let(:max_directory) { Gitlab::WikiPages::MAX_DIRECTORY_BYTES }
@@ -702,6 +749,50 @@ RSpec.describe WikiPage do
     end
   end
 
+  describe '#content_changed?' do
+    context 'with a new page' do
+      subject { new_page }
+
+      it 'returns false if content is nil' do
+        subject.attributes[:content] = nil
+
+        expect(subject.content_changed?).to be(false)
+      end
+
+      it 'returns true if content is set' do
+        subject.attributes[:content] = 'new'
+
+        expect(subject.content_changed?).to be(true)
+      end
+
+      it 'returns true if content is blank' do
+        subject.attributes[:content] = ''
+
+        expect(subject.content_changed?).to be(true)
+      end
+    end
+
+    context 'with an existing page' do
+      subject { existing_page }
+
+      it 'returns false' do
+        expect(subject.content_changed?).to be(false)
+      end
+
+      it 'returns false if content is set to the same value' do
+        subject.attributes[:content] = 'test content'
+
+        expect(subject.content_changed?).to be(false)
+      end
+
+      it 'returns true if content is changed' do
+        subject.attributes[:content] = 'new'
+
+        expect(subject.content_changed?).to be(true)
+      end
+    end
+  end
+
   describe '#path' do
     it 'returns the path when persisted' do
       expect(existing_page.path).to eq('test-page.md')