Limit the size of SVGs when viewing them as blobs

This ensures that SVGs greater than 2 megabytes are not scrubbed and
rendered. This in turn prevents requests from timing out due to
reading/scrubbing large SVGs potentially taking a lot of time (and
memory). The use of 2 megabytes is completely arbitrary.

Fixes gitlab-org/gitlab-ce#1435

CHANGELOG

@@ -32,6 +32,7 @@ v 8.11.0 (unreleased)
   - Add "No one can push" as an option for protected branches. !5081
   - Improve performance of AutolinkFilter#text_parse by using XPath
   - Add experimental Redis Sentinel support !1877
+  - Rendering of SVGs as blobs is now limited to SVGs with a size smaller or equal to 2MB
   - Fix branches page dropdown sort initial state (ClemMakesApps)
   - Environments have an url to link to
   - Various redundant database indexes have been removed

app/models/blob.rb

@@ -3,6 +3,9 @@ class Blob < SimpleDelegator
   CACHE_TIME = 60 # Cache raw blobs referred to by a (mutable) ref for 1 minute
   CACHE_TIME_IMMUTABLE = 3600 # Cache blobs referred to by an immutable reference for 1 hour
 
+  # The maximum size of an SVG that can be displayed.
+  MAXIMUM_SVG_SIZE = 2.megabytes
+
   # Wrap a Gitlab::Git::Blob object, or return nil when given nil
   #
   # This method prevents the decorated object from evaluating to "truthy" when
@@ -31,6 +34,10 @@ class Blob < SimpleDelegator
     text? && language && language.name == 'SVG'
   end
 
+  def size_within_svg_limits?
+    size <= MAXIMUM_SVG_SIZE
+  end
+
   def video?
     UploaderHelper::VIDEO_EXT.include?(extname.downcase.delete('.'))
   end

app/views/projects/blob/_image.html.haml

 .file-content.image_file
   - if blob.svg?
-    - # We need to scrub SVG but we cannot do so in the RawController: it would
-    - # be wrong/strange if RawController modified the data.
-    - blob.load_all_data!(@repository)
-    - blob = sanitize_svg(blob)
-    %img{src: "data:#{blob.mime_type};base64,#{Base64.encode64(blob.data)}"}
+    - if blob.size_within_svg_limits?
+      - # We need to scrub SVG but we cannot do so in the RawController: it would
+      - # be wrong/strange if RawController modified the data.
+      - blob.load_all_data!(@repository)
+      - blob = sanitize_svg(blob)
+      %img{src: "data:#{blob.mime_type};base64,#{Base64.encode64(blob.data)}"}
+    - else
+      .nothing-here-block
+        The SVG could not be displayed as it is too large, you can
+        #{link_to('view the raw file', namespace_project_raw_path(@project.namespace, @project, @id), target: '_blank')}
+        instead.
   - else
     %img{src: namespace_project_raw_path(@project.namespace, @project, tree_join(@commit.id, blob.path))}

spec/models/blob_spec.rb

@@ -94,4 +94,26 @@ describe Blob do
       expect(blob.to_partial_path).to eq 'download'
     end
   end
+
+  describe '#size_within_svg_limits?' do
+    let(:blob) { described_class.decorate(double(:blob)) }
+
+    it 'returns true when the blob size is smaller than the SVG limit' do
+      expect(blob).to receive(:size).and_return(42)
+
+      expect(blob.size_within_svg_limits?).to eq(true)
+    end
+
+    it 'returns true when the blob size is equal to the SVG limit' do
+      expect(blob).to receive(:size).and_return(Blob::MAXIMUM_SVG_SIZE)
+
+      expect(blob.size_within_svg_limits?).to eq(true)
+    end
+
+    it 'returns false when the blob size is larger than the SVG limit' do
+      expect(blob).to receive(:size).and_return(1.terabyte)
+
+      expect(blob.size_within_svg_limits?).to eq(false)
+    end
+  end
 end