Don't specify `shell` for Gitaly write-ref

Use shelling out to git to write refs instead of rugged, hoping to
avoid creating invalid refs.

To update HEAD we switched to using `git symbolic-ref`.

app/models/project.rb

@@ -1394,7 +1394,7 @@ class Project < ActiveRecord::Base
   def change_head(branch)
     if repository.branch_exists?(branch)
       repository.before_change_head
-      repository.raw_repository.write_ref('HEAD', "refs/heads/#{branch}", shell: false)
+      repository.raw_repository.write_ref('HEAD', "refs/heads/#{branch}")
       repository.copy_gitattributes(branch)
       repository.after_change_head
       reload_default_branch

app/models/repository.rb

@@ -259,7 +259,7 @@ class Repository
         next if kept_around?(sha)
 
         # This will still fail if the file is corrupted (e.g. 0 bytes)
-        raw_repository.write_ref(keep_around_ref_name(sha), sha, shell: false)
+        raw_repository.write_ref(keep_around_ref_name(sha), sha)
       rescue Gitlab::Git::CommandError => ex
         Rails.logger.error "Unable to create keep-around reference for repository #{disk_path}: #{ex}"
       end

changelogs/unreleased/bvl-use-shell-writeref.yml

+---
+title: Avoid creating invalid refs using rugged, shelling out for writing refs
+merge_request: 23286
+author:
+type: fixed

lib/gitlab/git/repository.rb

@@ -723,11 +723,11 @@ module Gitlab
         delete_refs(tmp_ref)
       end
 
-      def write_ref(ref_path, ref, old_ref: nil, shell: true)
+      def write_ref(ref_path, ref, old_ref: nil)
         ref_path = "#{Gitlab::Git::BRANCH_REF_PREFIX}#{ref_path}" unless ref_path.start_with?("refs/") || ref_path == "HEAD"
 
         wrapped_gitaly_errors do
-          gitaly_repository_client.write_ref(ref_path, ref, old_ref, shell)
+          gitaly_repository_client.write_ref(ref_path, ref, old_ref)
         end
       end
 

lib/gitlab/gitaly_client/repository_service.rb

@@ -251,12 +251,11 @@ module Gitlab
         )
       end
 
-      def write_ref(ref_path, ref, old_ref, shell)
+      def write_ref(ref_path, ref, old_ref)
         request = Gitaly::WriteRefRequest.new(
           repository: @gitaly_repo,
           ref: ref_path.b,
-          revision: ref.b,
-          shell: shell
+          revision: ref.b
         )
         request.old_revision = old_ref.b unless old_ref.nil?
 

spec/lib/gitlab/git/repository_spec.rb

@@ -1469,6 +1469,19 @@ describe Gitlab::Git::Repository, :seed_helper do
         end
       end
     end
+
+    it 'writes the HEAD' do
+      repository.write_ref('HEAD', 'refs/heads/feature')
+
+      expect(repository.commit('HEAD')).to eq(repository.commit('feature'))
+      expect(repository.root_ref).to eq('feature')
+    end
+
+    it 'writes other refs' do
+      repository.write_ref('refs/heads/feature', SeedRepo::Commit::ID)
+
+      expect(repository.commit('feature').sha).to eq(SeedRepo::Commit::ID)
+    end
   end
 
   describe '#write_config' do

spec/models/project_spec.rb

@@ -2203,12 +2203,6 @@ describe Project do
       project.change_head(project.default_branch)
     end
 
-    it 'creates the new reference with rugged' do
-      expect(project.repository.raw_repository).to receive(:write_ref).with('HEAD', "refs/heads/#{project.default_branch}", shell: false)
-
-      project.change_head(project.default_branch)
-    end
-
     it 'copies the gitattributes' do
       expect(project.repository).to receive(:copy_gitattributes).with(project.default_branch)
       project.change_head(project.default_branch)