Prevent users from deleting Webhooks via API they do not own

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15576

CHANGELOG

@@ -4,6 +4,7 @@ v 8.8.0 (unreleased)
   - Remove future dates from contribution calendar graph.
 
 v 8.7.1 (unreleased)
+  - Prevent users from deleting Webhooks via API they do not own
   - Use the `can?` helper instead of `current_user.can?`
 
 v 8.7.0

lib/api/project_hooks.rb

@@ -103,10 +103,10 @@ module API
         required_attributes! [:hook_id]
 
         begin
-          @hook = ProjectHook.find(params[:hook_id])
-          @hook.destroy
+          @hook = user_project.hooks.destroy(params[:hook_id])
         rescue
           # ProjectHook can raise Error if hook_id not found
+          not_found!("Error deleting hook #{params[:hook_id]}")
         end
       end
     end

spec/requests/api/project_hooks_spec.rb

@@ -148,14 +148,24 @@ describe API::API, 'ProjectHooks', api: true do
       expect(response.status).to eq(200)
     end
 
-    it "should return success when deleting non existent hook" do
+    it "should return a 404 error when deleting non existent hook" do
       delete api("/projects/#{project.id}/hooks/42", user)
-      expect(response.status).to eq(200)
+      expect(response.status).to eq(404)
     end
 
     it "should return a 405 error if hook id not given" do
       delete api("/projects/#{project.id}/hooks", user)
       expect(response.status).to eq(405)
     end
+
+    it "shold return a 404 if a user attempts to delete project hooks he/she does not own" do
+      test_user = create(:user)
+      other_project = create(:project)
+      other_project.team << [test_user, :master]
+
+      delete api("/projects/#{other_project.id}/hooks/#{hook.id}", test_user)
+      expect(response.status).to eq(404)
+      expect(WebHook.exists?(hook.id)).to be_truthy
+    end
   end
 end