Prevent Billion Laughs attack

It keeps track of the memory being used when loading the YAML file
as well as the depth of nesting.
Track exception when YAML is too big

3 files changed, 132 insertions, 4 deletions

diff --git a/spec/lib/gitlab/ci/config_spec.rb b/spec/lib/gitlab/ci/config_spec.rb
index 7f336ee853e..4e8bff3d738 100644
--- a/spec/lib/gitlab/ci/config_spec.rb
+++ b/spec/lib/gitlab/ci/config_spec.rb
@@ -90,6 +90,27 @@ describe Gitlab::Ci::Config do
       end
     end
 
+    context 'when yml is too big' do
+      let(:yml) do
+        <<~YAML
+          --- &1
+          - hi
+          - *1
+        YAML
+      end
+
+      describe '.new' do
+        it 'raises error' do
+          expect(Gitlab::Sentry).to receive(:track_exception)
+
+          expect { config }.to raise_error(
+            described_class::ConfigError,
+            /The parsed YAML is too big/
+          )
+        end
+      end
+    end
+
     context 'when config logic is incorrect' do
       let(:yml) { 'before_script: "ls"' }
 
diff --git a/spec/lib/gitlab/config/loader/yaml_spec.rb b/spec/lib/gitlab/config/loader/yaml_spec.rb
index 44c9a3896a8..0affeb01f6a 100644
--- a/spec/lib/gitlab/config/loader/yaml_spec.rb
+++ b/spec/lib/gitlab/config/loader/yaml_spec.rb
@@ -8,7 +8,7 @@ describe Gitlab::Config::Loader::Yaml do
 
     describe '#valid?' do
       it 'returns true' do
-        expect(loader.valid?).to be true
+        expect(loader).to be_valid
       end
     end
 
@@ -24,7 +24,7 @@ describe Gitlab::Config::Loader::Yaml do
 
     describe '#valid?' do
       it 'returns false' do
-        expect(loader.valid?).to be false
+        expect(loader).not_to be_valid
       end
     end
 
@@ -43,7 +43,10 @@ describe Gitlab::Config::Loader::Yaml do
 
     describe '#initialize' do
       it 'raises FormatError' do
-        expect { loader }.to raise_error(Gitlab::Config::Loader::FormatError, 'Unknown alias: bad_alias')
+        expect { loader }.to raise_error(
+          Gitlab::Config::Loader::FormatError,
+          'Unknown alias: bad_alias'
+        )
       end
     end
   end
@@ -53,7 +56,68 @@ describe Gitlab::Config::Loader::Yaml do
 
     describe '#valid?' do
       it 'returns false' do
-        expect(loader.valid?).to be false
+        expect(loader).not_to be_valid
+      end
+    end
+  end
+
+  # Prevent Billion Laughs attack: https://gitlab.com/gitlab-org/gitlab-ce/issues/56018
+  context 'when yaml size is too large' do
+    let(:yml) do
+      <<~YAML
+        a: &a ["lol","lol","lol","lol","lol","lol","lol","lol","lol"]
+        b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
+        c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
+        d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
+        e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
+        f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
+        g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
+        h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
+        i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]
+      YAML
+    end
+
+    describe '#valid?' do
+      it 'returns false' do
+        expect(loader).not_to be_valid
+      end
+
+      it 'returns true if "ci_yaml_limit_size" feature flag is disabled' do
+        stub_feature_flags(ci_yaml_limit_size: false)
+
+        expect(loader).to be_valid
+      end
+    end
+
+    describe '#load!' do
+      it 'raises FormatError' do
+        expect { loader.load! }.to raise_error(
+          Gitlab::Config::Loader::FormatError,
+          'The parsed YAML is too big'
+        )
+      end
+    end
+  end
+
+  # Prevent Billion Laughs attack: https://gitlab.com/gitlab-org/gitlab-ce/issues/56018
+  context 'when yaml has cyclic data structure' do
+    let(:yml) do
+      <<~YAML
+        --- &1
+        - hi
+        - *1
+      YAML
+    end
+
+    describe '#valid?' do
+      it 'returns false' do
+        expect(loader.valid?).to be(false)
+      end
+    end
+
+    describe '#load!' do
+      it 'raises FormatError' do
+        expect { loader.load! }.to raise_error(Gitlab::Config::Loader::FormatError, 'The parsed YAML is too big')
       end
     end
   end
diff --git a/spec/lib/gitlab/utils/deep_size_spec.rb b/spec/lib/gitlab/utils/deep_size_spec.rb
new file mode 100644
index 00000000000..1e619a15980
--- /dev/null
+++ b/spec/lib/gitlab/utils/deep_size_spec.rb
@@ -0,0 +1,43 @@
+require 'spec_helper'
+
+describe Gitlab::Utils::DeepSize do
+  let(:data) do
+    {
+      a: [1, 2, 3],
+      b: {
+        c: [4, 5],
+        d: [
+          { e: [[6], [7]] }
+        ]
+      }
+    }
+  end
+
+  let(:max_size) { 1.kilobyte }
+  let(:max_depth) { 10 }
+  let(:deep_size) { described_class.new(data, max_size: max_size, max_depth: max_depth) }
+
+  describe '#evaluate' do
+    context 'when data within size and depth limits' do
+      it 'returns true' do
+        expect(deep_size).to be_valid
+      end
+    end
+
+    context 'when data not within size limit' do
+      let(:max_size) { 200.bytes }
+
+      it 'returns false' do
+        expect(deep_size).not_to be_valid
+      end
+    end
+
+    context 'when data not within depth limit' do
+      let(:max_depth) { 2 }
+
+      it 'returns false' do
+        expect(deep_size).not_to be_valid
+      end
+    end
+  end
+end