Validate build traces using CRC32 checksums

This commit adds a mechanism for validating correctness of build logs
using CRC32 checksum algorithm.

app/models/ci/build_trace_chunk.rb

@@ -29,6 +29,7 @@ module Ci
     }
 
     scope :live, -> { redis }
+    scope :persisted, -> { not_redis.order(:chunk_index) }
 
     class << self
       def all_stores
@@ -63,12 +64,24 @@ module Ci
           get_store_class(store).delete_keys(value)
         end
       end
+
+      ##
+      # Sometimes we do not want to read raw data. This method makes it easier
+      # to find attributes that are just metadata excluding raw data.
+      #
+      def metadata_attributes
+        attribute_names - %w[raw_data]
+      end
     end
 
     def data
       @data ||= get_data.to_s
     end
 
+    def crc32
+      checksum.to_i
+    end
+
     def truncate(offset = 0)
       raise ArgumentError, 'Offset is out of range' if offset > size || offset < 0
       return if offset == size # Skip the following process as it doesn't affect anything
@@ -150,7 +163,7 @@ module Ci
 
       self.raw_data = nil
       self.data_store = new_store
-      self.checksum = crc32(current_data)
+      self.checksum = self.class.crc32(current_data)
 
       ##
       # We need to so persist data then save a new store identifier before we

app/models/ci/build_trace_chunks/database.rb

@@ -17,6 +17,8 @@ module Ci
 
       def data(model)
         model.raw_data
+      rescue ActiveModel::MissingAttributeError
+        model.reset.raw_data
       end
 
       def set_data(model, new_data)

app/models/concerns/checksummable.rb

@@ -3,11 +3,11 @@
 module Checksummable
   extend ActiveSupport::Concern
 
-  def crc32(data)
-    Zlib.crc32(data)
-  end
-
   class_methods do
+    def crc32(data)
+      Zlib.crc32(data)
+    end
+
     def hexdigest(path)
       ::Digest::SHA256.file(path).hexdigest
     end

app/services/ci/update_build_state_service.rb

@@ -2,6 +2,8 @@
 
 module Ci
   class UpdateBuildStateService
+    include Gitlab::Utils::StrongMemoize
+
     Result = Struct.new(:status, :backoff, keyword_init: true)
 
     ACCEPT_TIMEOUT = 5.minutes.freeze
@@ -16,11 +18,12 @@ module Ci
 
     def execute
       overwrite_trace! if has_trace?
+      create_pending_state! if accept_available?
 
       if accept_request?
         accept_build_state!
       else
-        check_migration_state
+        validate_build_trace!
         update_build_state!
       end
     end
@@ -28,9 +31,7 @@ module Ci
     private
 
     def accept_build_state!
-      state_created = ensure_pending_state.created_at
-
-      if Time.current - state_created > ACCEPT_TIMEOUT
+      if Time.current - pending_state.created_at > ACCEPT_TIMEOUT
         metrics.increment_trace_operation(operation: :discarded)
 
         return update_build_state!
@@ -42,7 +43,7 @@ module Ci
 
       metrics.increment_trace_operation(operation: :accepted)
 
-      ::Gitlab::Ci::Runner::Backoff.new(state_created).then do |backoff|
+      ::Gitlab::Ci::Runner::Backoff.new(pending_state.created_at).then do |backoff|
         Result.new(status: 202, backoff: backoff.to_seconds)
       end
     end
@@ -53,12 +54,20 @@ module Ci
       build.trace.set(params[:trace]) if Gitlab::Ci::Features.trace_overwrite?
     end
 
-    def check_migration_state
+    def create_pending_state!
+      pending_state.created_at
+    end
+
+    def validate_build_trace!
       return unless accept_available?
 
-      if has_chunks? && !live_chunks_pending?
-        metrics.increment_trace_operation(operation: :finalized)
+      unless ::Gitlab::Ci::Trace::Checksum.new(build).valid?
+        metrics.increment_trace_operation(operation: :invalid)
       end
+
+      return unless chunks_persisted?
+
+      metrics.increment_trace_operation(operation: :finalized)
     end
 
     def update_build_state!
@@ -100,18 +109,22 @@ module Ci
       params.dig(:checksum).present?
     end
 
-    def has_chunks?
-      build.trace_chunks.any?
-    end
-
     def live_chunks_pending?
       build.trace_chunks.live.any?
     end
 
+    def chunks_persisted?
+      build.trace_chunks.any? && !live_chunks_pending?
+    end
+
     def build_running?
       build_state == 'running'
     end
 
+    def pending_state
+      strong_memoize(:pending_state) { ensure_pending_state }
+    end
+
     def ensure_pending_state
       Ci::BuildPendingState.create_or_find_by!(
         build_id: build.id,

changelogs/unreleased/feature-gb-validate-build-traces.yml

+---
+title: Validate build traces using CRC32 checksums
+merge_request: 42829
+author:
+type: added

lib/gitlab/ci/trace/checksum.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    class Trace
+      ##
+      # Trace::Checksum class is responsible for calculating a CRC32 checksum
+      # of an entire build trace using partial build trace chunks stored in a
+      # database.
+      #
+      # CRC32 checksum can be easily calculated by combining partial checksums
+      # in a right order.
+      #
+      # Then we compare CRC32 checksum provided by a GitLab Runner and expect
+      # it to be the same as the CRC32 checksum derived from partial chunks.
+      #
+      class Checksum
+        include Gitlab::Utils::StrongMemoize
+
+        attr_reader :build
+
+        def initialize(build)
+          @build = build
+        end
+
+        def valid?
+          return false unless state_crc32 > 0
+
+          state_crc32 == chunks_crc32
+        end
+
+        def state_crc32
+          strong_memoize(:crc32) do
+            build.pending_state&.trace_checksum.then do |checksum|
+              checksum.to_s.split('crc32:').last.to_i
+            end
+          end
+        end
+
+        def chunks_crc32
+          trace_chunks.reduce(0) do |crc32, chunk|
+            Zlib.crc32_combine(crc32, chunk.crc32, chunk_size(chunk))
+          end
+        end
+
+        def chunks_count
+          strong_memoize(:chunks_count) do
+            build.trace_chunks.maximum(:chunk_index)
+          end
+        end
+
+        ##
+        # Trace chunks will be persisted in a database if an object store is
+        # not configured - in that case we do not want to load entire raw data
+        # of all the chunks into memory.
+        #
+        # We ignore `raw_data` attribute instead, and rely on internal build
+        # trace chunk database adapter to handle
+        # `ActiveModel::MissingAttributeError` exception.
+        #
+        # Alternative solution would be separating chunk data from chunk
+        # metadata on the database level too.
+        #
+        def trace_chunks
+          build.trace_chunks.persisted
+            .select(::Ci::BuildTraceChunk.metadata_attributes)
+        end
+
+        private
+
+        def chunk_size(chunk)
+          if chunk.chunk_index == chunks_count
+            chunk.size
+          else
+            ::Ci::BuildTraceChunk::CHUNK_SIZE
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/ci/trace/metrics.rb

@@ -7,7 +7,7 @@ module Gitlab
         extend Gitlab::Utils::StrongMemoize
 
         OPERATIONS = [:appended, :streamed, :chunked, :mutated, :overwrite,
-                      :accepted, :finalized, :discarded, :conflict].freeze
+                      :accepted, :finalized, :discarded, :conflict, :invalid].freeze
 
         def increment_trace_operation(operation: :unknown)
           unless OPERATIONS.include?(operation)

spec/factories/ci/build_trace_chunks.rb

@@ -53,5 +53,18 @@ FactoryBot.define do
     trait :fog_without_data do
       data_store { :fog }
     end
+
+    trait :persisted do
+      data_store { :database}
+
+      transient do
+        initial_data { 'test data' }
+      end
+
+      after(:build) do |chunk, evaluator|
+        Ci::BuildTraceChunks::Database.new.set_data(chunk, evaluator.initial_data)
+        chunk.checksum = chunk.class.crc32(evaluator.initial_data)
+      end
+    end
   end
 end

spec/lib/gitlab/ci/trace/checksum_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Ci::Trace::Checksum do
+  let(:build) { create(:ci_build, :running) }
+
+  subject { described_class.new(build) }
+
+  context 'when build pending state exits' do
+    before do
+      create(:ci_build_pending_state, build: build, trace_checksum: 'crc32:3564598592')
+    end
+
+    context 'when matching persisted trace chunks exist' do
+      before do
+        create_chunk(index: 0, data: 'a' * 128.kilobytes)
+        create_chunk(index: 1, data: 'b' * 128.kilobytes)
+        create_chunk(index: 2, data: 'ccccccccccccccccc')
+      end
+
+      it 'calculates combined trace chunks CRC32 correctly' do
+        expect(subject.chunks_crc32).to eq 3564598592
+        expect(subject).to be_valid
+      end
+    end
+
+    context 'when trace chunks were persisted in a wrong order' do
+      before do
+        create_chunk(index: 0, data: 'b' * 128.kilobytes)
+        create_chunk(index: 1, data: 'a' * 128.kilobytes)
+        create_chunk(index: 2, data: 'ccccccccccccccccc')
+      end
+
+      it 'makes trace checksum invalid' do
+        expect(subject).not_to be_valid
+      end
+    end
+
+    context 'when one of the trace chunks is missing' do
+      before do
+        create_chunk(index: 0, data: 'a' * 128.kilobytes)
+        create_chunk(index: 2, data: 'ccccccccccccccccc')
+      end
+
+      it 'makes trace checksum invalid' do
+        expect(subject).not_to be_valid
+      end
+    end
+
+    context 'when checksums of persisted trace chunks do not match' do
+      before do
+        create_chunk(index: 0, data: 'a' * 128.kilobytes)
+        create_chunk(index: 1, data: 'X' * 128.kilobytes)
+        create_chunk(index: 2, data: 'ccccccccccccccccc')
+      end
+
+      it 'makes trace checksum invalid' do
+        expect(subject).not_to be_valid
+      end
+    end
+
+    context 'when persisted trace chunks are missing' do
+      it 'makes trace checksum invalid' do
+        expect(subject.state_crc32).to eq 3564598592
+        expect(subject).not_to be_valid
+      end
+    end
+  end
+
+  context 'when build pending state is missing' do
+    describe '#state_crc32' do
+      it 'returns zero' do
+        expect(subject.state_crc32).to be_zero
+      end
+    end
+
+    describe '#valid?' do
+      it { is_expected.not_to be_valid }
+    end
+  end
+
+  describe '#trace_chunks' do
+    before do
+      create_chunk(index: 0, data: 'abcdefg')
+    end
+
+    it 'does not load raw_data from a database store' do
+      subject.trace_chunks.first.then do |chunk|
+        expect(chunk).to be_database
+        expect { chunk.raw_data }
+          .to raise_error ActiveModel::MissingAttributeError
+      end
+    end
+  end
+
+  def create_chunk(index:, data:)
+    create(:ci_build_trace_chunk, :persisted, build: build,
+                                              chunk_index: index,
+                                              initial_data: data)
+  end
+end

spec/models/concerns/checksummable_spec.rb

@@ -3,17 +3,21 @@
 require 'spec_helper'
 
 RSpec.describe Checksummable do
-  describe ".hexdigest" do
-    let(:fake_class) do
-      Class.new do
-        include Checksummable
-      end
+  subject do
+    Class.new { include Checksummable }
+  end
+
+  describe ".crc32" do
+    it 'returns the CRC32 of data' do
+      expect(subject.crc32('abcd')).to eq 3984772369
     end
+  end
 
+  describe ".hexdigest" do
     it 'returns the SHA256 sum of the file' do
       expected = Digest::SHA256.file(__FILE__).hexdigest
 
-      expect(fake_class.hexdigest(__FILE__)).to eq(expected)
+      expect(subject.hexdigest(__FILE__)).to eq(expected)
     end
   end
 end

spec/requests/api/ci/runner/jobs_put_spec.rb

@@ -145,7 +145,7 @@ RSpec.describe API::Ci::Runner, :clean_gitlab_redis_shared_state do
                   update_job(state: 'success', checksum: 'crc:12345678')
 
                   expect(job.reload).to be_success
-                  expect(job.pending_state).not_to be_present
+                  expect(job.pending_state).to be_present
                   expect(response).to have_gitlab_http_status(:ok)
                   expect(response.header).not_to have_key('X-GitLab-Trace-Update-Interval')
                 end

spec/services/ci/update_build_state_service_spec.rb

@@ -85,7 +85,7 @@ RSpec.describe Ci::UpdateBuildStateService do
 
     context 'when build trace has been migrated' do
       before do
-        create(:ci_build_trace_chunk, :database_with_data, build: build)
+        create(:ci_build_trace_chunk, :persisted, build: build, initial_data: 'abcd')
       end
 
       it 'updates a build state' do
@@ -113,6 +113,28 @@ RSpec.describe Ci::UpdateBuildStateService do
           .to have_received(:increment_trace_operation)
           .with(operation: :finalized)
       end
+
+      context 'when trace checksum is not valid' do
+        it 'increments invalid trace metric' do
+          execute_with_stubbed_metrics!
+
+          expect(metrics)
+            .to have_received(:increment_trace_operation)
+            .with(operation: :invalid)
+        end
+      end
+
+      context 'when trace checksum is valid' do
+        let(:params) { { checksum: 'crc32:3984772369', state: 'success' } }
+
+        it 'does not increment invalid trace metric' do
+          execute_with_stubbed_metrics!
+
+          expect(metrics)
+            .not_to have_received(:increment_trace_operation)
+            .with(operation: :invalid)
+        end
+      end
     end
 
     context 'when build trace has not been migrated yet' do
@@ -146,14 +168,6 @@ RSpec.describe Ci::UpdateBuildStateService do
         subject.execute
       end
 
-      it 'increments trace accepted operation metric' do
-        execute_with_stubbed_metrics!
-
-        expect(metrics)
-          .to have_received(:increment_trace_operation)
-          .with(operation: :accepted)
-      end
-
       it 'creates a pending state record' do
         subject.execute
 
@@ -165,6 +179,22 @@ RSpec.describe Ci::UpdateBuildStateService do
         end
       end
 
+      it 'increments trace accepted operation metric' do
+        execute_with_stubbed_metrics!
+
+        expect(metrics)
+          .to have_received(:increment_trace_operation)
+          .with(operation: :accepted)
+      end
+
+      it 'does not increment invalid trace metric' do
+        execute_with_stubbed_metrics!
+
+        expect(metrics)
+          .not_to have_received(:increment_trace_operation)
+          .with(operation: :invalid)
+      end
+
       context 'when build pending state is outdated' do
         before do
           build.create_pending_state(