Add user deletion permission check in `Users::DestroyService`

We saw from a recent incident that the `Users::DestroyService` would
attempt to delete a user over and over. Revoking the permissions
from the current user did not help. We should ensure that the
current user does, in fact, have permissions to delete the user.

Signed-off-by: Rémy Coutable <remy@rymai.me>

1 files changed, 26 insertions, 5 deletions

diff --git a/spec/services/users/destroy_spec.rb b/spec/services/users/destroy_spec.rb
index 46e58393218..c0bf27c698c 100644
--- a/spec/services/users/destroy_spec.rb
+++ b/spec/services/users/destroy_spec.rb
@@ -2,11 +2,11 @@ require 'spec_helper'
 
 describe Users::DestroyService, services: true do
   describe "Deletes a user and all their personal projects" do
-    let!(:user)         { create(:user) }
-    let!(:current_user) { create(:user) }
-    let!(:namespace)    { create(:namespace, owner: user) }
-    let!(:project)      { create(:project, namespace: namespace) }
-    let(:service)       { described_class.new(current_user) }
+    let!(:user)      { create(:user) }
+    let!(:admin)     { create(:admin) }
+    let!(:namespace) { create(:namespace, owner: user) }
+    let!(:project)   { create(:project, namespace: namespace) }
+    let(:service)    { described_class.new(admin) }
 
     context 'no options are given' do
       it 'deletes the user' do
@@ -57,5 +57,26 @@ describe Users::DestroyService, services: true do
         expect { User.find(user.id) }.to raise_error(ActiveRecord::RecordNotFound)
       end
     end
+
+    context "deletion permission checks" do
+      it 'does not delete the user when user is not an admin' do
+        other_user = create(:user)
+
+        expect { described_class.new(other_user).execute(user) }.to raise_error(Gitlab::Access::AccessDeniedError)
+        expect(User.exists?(user.id)).to be(true)
+      end
+
+      it 'allows admins to delete anyone' do
+        described_class.new(admin).execute(user)
+
+        expect(User.exists?(user.id)).to be(false)
+      end
+
+      it 'allows users to delete their own account' do
+        described_class.new(user).execute(user)
+
+        expect(User.exists?(user.id)).to be(false)
+      end
+    end
   end
 end