Only assign merge params when allowed

When a user updates a merge request coming from a fork, they should
not be able to set `force_remove_source_branch` if they cannot push
code to the source project.

Otherwise developers of the target project could remove the source
branch of the source project by setting this flag through the API.

6 files changed, 133 insertions, 6 deletions

diff --git a/spec/requests/api/merge_requests_spec.rb b/spec/requests/api/merge_requests_spec.rb
index 8179da2f97c..05160a33e61 100644
--- a/spec/requests/api/merge_requests_spec.rb
+++ b/spec/requests/api/merge_requests_spec.rb
@@ -1737,6 +1737,38 @@ describe API::MergeRequests do
         expect(json_response['state']).to eq('closed')
         expect(json_response['force_remove_source_branch']).to be_truthy
       end
+
+      context 'with a merge request across forks' do
+        let(:fork_owner) { create(:user) }
+        let(:source_project) { fork_project(project, fork_owner) }
+        let(:target_project) { project }
+
+        let(:merge_request) do
+          create(:merge_request,
+                 source_project: source_project,
+                 target_project: target_project,
+                 source_branch: 'fixes',
+                 merge_params: { 'force_remove_source_branch' => false })
+        end
+
+        it 'is true for an authorized user' do
+          put api("/projects/#{target_project.id}/merge_requests/#{merge_request.iid}", fork_owner), params: { state_event: 'close', remove_source_branch: true }
+
+          expect(response).to have_gitlab_http_status(200)
+          expect(json_response['state']).to eq('closed')
+          expect(json_response['force_remove_source_branch']).to be true
+        end
+
+        it 'is false for an unauthorized user' do
+          expect do
+            put api("/projects/#{target_project.id}/merge_requests/#{merge_request.iid}", target_project.owner), params: { state_event: 'close', remove_source_branch: true }
+          end.not_to change { merge_request.reload.merge_params }
+
+          expect(response).to have_gitlab_http_status(200)
+          expect(json_response['state']).to eq('closed')
+          expect(json_response['force_remove_source_branch']).to be false
+        end
+      end
     end
 
     context "to close a MR" do
diff --git a/spec/services/auto_merge/base_service_spec.rb b/spec/services/auto_merge/base_service_spec.rb
index a409f21a7e4..0a6bcb1badc 100644
--- a/spec/services/auto_merge/base_service_spec.rb
+++ b/spec/services/auto_merge/base_service_spec.rb
@@ -51,7 +51,7 @@ describe AutoMerge::BaseService do
         expect(merge_request.merge_params['commit_message']).to eq("Merge branch 'patch-12' into 'master'")
         expect(merge_request.merge_params['sha']).to eq('200fcc9c260f7219eaf0daba87d818f0922c5b18')
         expect(merge_request.merge_params['should_remove_source_branch']).to eq(false)
-        expect(merge_request.merge_params['squash']).to eq(false)
+        expect(merge_request.squash).to eq(false)
         expect(merge_request.merge_params['squash_commit_message']).to eq('Update README.md')
       end
     end
@@ -108,7 +108,6 @@ describe AutoMerge::BaseService do
           'commit_message' => "Merge branch 'patch-12' into 'master'",
           'sha' => "200fcc9c260f7219eaf0daba87d818f0922c5b18",
           'should_remove_source_branch' => false,
-          'squash' => false,
           'squash_commit_message' => "Update README.md"
         }
       end
diff --git a/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb b/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb
index 931b52470c4..ccbb4e7c30d 100644
--- a/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb
+++ b/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb
@@ -59,8 +59,9 @@ describe AutoMerge::MergeWhenPipelineSucceedsService do
       it 'sets the params, merge_user, and flag' do
         expect(merge_request).to be_valid
         expect(merge_request.merge_when_pipeline_succeeds).to be_truthy
-        expect(merge_request.merge_params).to include commit_message: 'Awesome message'
+        expect(merge_request.merge_params).to include 'commit_message' => 'Awesome message'
         expect(merge_request.merge_user).to be user
+        expect(merge_request.auto_merge_strategy).to eq AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
       end
 
       it 'creates a system note' do
@@ -73,7 +74,7 @@ describe AutoMerge::MergeWhenPipelineSucceedsService do
     end
 
     context 'already approved' do
-      let(:service) { described_class.new(project, user, new_key: true) }
+      let(:service) { described_class.new(project, user, should_remove_source_branch: true) }
       let(:build)   { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch) }
 
       before do
@@ -90,7 +91,7 @@ describe AutoMerge::MergeWhenPipelineSucceedsService do
         expect(SystemNoteService).not_to receive(:merge_when_pipeline_succeeds)
 
         service.execute(mr_merge_if_green_enabled)
-        expect(mr_merge_if_green_enabled.merge_params).to have_key(:new_key)
+        expect(mr_merge_if_green_enabled.merge_params).to have_key('should_remove_source_branch')
       end
     end
   end
diff --git a/spec/services/concerns/merge_requests/assigns_merge_params_spec.rb b/spec/services/concerns/merge_requests/assigns_merge_params_spec.rb
new file mode 100644
index 00000000000..5b653aa331c
--- /dev/null
+++ b/spec/services/concerns/merge_requests/assigns_merge_params_spec.rb
@@ -0,0 +1,70 @@
+require 'spec_helper'
+
+describe MergeRequests::AssignsMergeParams do
+  it 'raises an error when used from an instance that does not respond to #current_user' do
+    define_class = -> { Class.new { include MergeRequests::AssignsMergeParams }.new }
+
+    expect { define_class.call }.to raise_error %r{can not be included in (.*) without implementing #current_user}
+  end
+
+  describe '#assign_allowed_merge_params' do
+    let(:merge_request) { build(:merge_request) }
+
+    let(:params) do
+      { commit_message: 'Commit Message',
+        'should_remove_source_branch' => true,
+        unknown_symbol: 'Unknown symbol',
+        'unknown_string' => 'Unknown String' }
+    end
+
+    subject(:merge_request_service) do
+      Class.new do
+        attr_accessor :current_user
+
+        include MergeRequests::AssignsMergeParams
+
+        def initialize(user)
+          @current_user = user
+        end
+      end
+    end
+
+    it 'only assigns known parameters to the merge request' do
+      service = merge_request_service.new(merge_request.author)
+
+      service.assign_allowed_merge_params(merge_request, params)
+
+      expect(merge_request.merge_params).to eq('commit_message' => 'Commit Message', 'should_remove_source_branch' => true)
+    end
+
+    it 'returns a hash without the known merge params' do
+      service = merge_request_service.new(merge_request.author)
+
+      result = service.assign_allowed_merge_params(merge_request, params)
+
+      expect(result).to eq({ 'unknown_symbol' => 'Unknown symbol', 'unknown_string' => 'Unknown String' })
+    end
+
+    context 'the force_remove_source_branch param' do
+      let(:params) { { force_remove_source_branch: true } }
+
+      it 'assigns the param if the user is allowed to do that' do
+        service = merge_request_service.new(merge_request.author)
+
+        result = service.assign_allowed_merge_params(merge_request, params)
+
+        expect(merge_request.force_remove_source_branch?).to be true
+        expect(result).to be_empty
+      end
+
+      it 'only removes the param if the user is not allowed to do that' do
+        service = merge_request_service.new(build(:user))
+
+        result = service.assign_allowed_merge_params(merge_request, params)
+
+        expect(merge_request.force_remove_source_branch?).to be_falsy
+        expect(result).to be_empty
+      end
+    end
+  end
+end
diff --git a/spec/services/merge_requests/build_service_spec.rb b/spec/services/merge_requests/build_service_spec.rb
index d546a092680..68e53553043 100644
--- a/spec/services/merge_requests/build_service_spec.rb
+++ b/spec/services/merge_requests/build_service_spec.rb
@@ -83,8 +83,9 @@ describe MergeRequests::BuildService do
       expect(merge_request.force_remove_source_branch?).to be_falsey
     end
 
-    context 'with force_remove_source_branch parameter' do
+    context 'with force_remove_source_branch parameter when the user is authorized' do
       let(:mr_params) { params.merge(force_remove_source_branch: '1') }
+      let(:source_project) { fork_project(project, user) }
       let(:merge_request) { described_class.new(project, user, mr_params).execute }
 
       it 'assigns force_remove_source_branch' do
diff --git a/spec/services/merge_requests/update_service_spec.rb b/spec/services/merge_requests/update_service_spec.rb
index d3c4c436901..d31f5dc0176 100644
--- a/spec/services/merge_requests/update_service_spec.rb
+++ b/spec/services/merge_requests/update_service_spec.rb
@@ -646,5 +646,29 @@ describe MergeRequests::UpdateService, :mailer do
         expect(merge_request.allow_collaboration).to be_truthy
       end
     end
+
+    context 'updating `force_remove_source_branch`' do
+      let(:target_project) { create(:project, :repository, :public) }
+      let(:source_project) { fork_project(target_project, nil, repository: true) }
+      let(:user) { target_project.owner }
+      let(:merge_request) do
+        create(:merge_request,
+               source_project: source_project,
+               source_branch: 'fixes',
+               target_project: target_project)
+      end
+
+      it "cannot be done by members of the target project when they don't have access" do
+        expect { update_merge_request(force_remove_source_branch: true) }
+          .not_to change { merge_request.reload.force_remove_source_branch? }.from(nil)
+      end
+
+      it 'can be done by members of the target project if they can push to the source project' do
+        source_project.add_developer(user)
+
+        expect { update_merge_request(force_remove_source_branch: true) }
+          .to change { merge_request.reload.force_remove_source_branch? }.from(nil).to(true)
+      end
+    end
   end
 end