From 93e4efb74294f1c51529187bbfd3b73cd46a3544 Mon Sep 17 00:00:00 2001
From: Stephen Paul Weber <singpolyma@singpolyma.net>
Date: Sun, 28 Apr 2019 13:33:22 -0500
Subject: [PATCH] Default max import depth of 50

So even without a timeout, there is a limit on bonkers cases.

Standard resolver defaults to INIFINTY since the standard does not
define a depth limit.
---
 .rubocop.yml         |  3 +++
 lib/dhall/resolve.rb | 30 ++++++++++++++++++++----------
 test/test_resolve.rb | 21 +++++++++++++++++++++
 3 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/.rubocop.yml b/.rubocop.yml
index 6940451..d7b00fb 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -20,6 +20,9 @@ Metrics/BlockLength:
   Exclude:
     - dhall.gemspec
 
+Metrics/ParameterLists:
+  CountKeywordArgs: false
+
 Metrics/ModuleLength:
   Enabled: false
 
diff --git a/lib/dhall/resolve.rb b/lib/dhall/resolve.rb
index 250b55b..1a8888c 100644
--- a/lib/dhall/resolve.rb
+++ b/lib/dhall/resolve.rb
@@ -150,8 +150,9 @@ module Dhall
 		end
 
 		class ResolutionSet
-			def initialize(reader)
+			def initialize(reader, max_depth:)
 				@reader = reader
+				@max_depth = max_depth
 				@parents = []
 				@set = Hash.new { |h, k| h[k] = [] }
 			end
@@ -160,6 +161,9 @@ module Dhall
 				p = Promise.new
 				if @parents.include?(source.canonical)
 					p.reject(ImportLoopException.new(source))
+				elsif @parents.length + 1 > @max_depth
+					msg = "Max import depth of #{@max_depth} exceeded"
+					p.reject(ImportFailedException.new(msg))
 				else
 					@set[source] << p
 				end
@@ -215,12 +219,15 @@ module Dhall
 				path_reader: ReadPathSources,
 				http_reader: StandardReadHttpSources,
 				https_reader: http_reader,
-				environment_reader: ReadEnvironmentSources
+				environment_reader: ReadEnvironmentSources,
+				max_depth: Float::INFINITY
 			)
-				@path_resolutions = ResolutionSet.new(path_reader)
-				@http_resolutions = ResolutionSet.new(http_reader)
-				@https_resolutions = ResolutionSet.new(https_reader)
-				@env_resolutions = ResolutionSet.new(environment_reader)
+				@path_resolutions = ResolutionSet.new(path_reader, max_depth: max_depth)
+				@http_resolutions = ResolutionSet.new(http_reader, max_depth: max_depth)
+				@https_resolutions = ResolutionSet.new(https_reader, max_depth: max_depth)
+				@env_resolutions = ResolutionSet.new(
+					environment_reader, max_depth: max_depth
+				)
 				@deadline = Util::NoDeadline.new
 				@cache = {}
 			end
@@ -307,7 +314,8 @@ module Dhall
 				http_reader: ReadHttpSources,
 				https_reader: http_reader,
 				environment_reader: ReadEnvironmentSources,
-				ipfs_public_gateway: "cloudflare-ipfs.com"
+				ipfs_public_gateway: "cloudflare-ipfs.com",
+				max_depth: 50
 			)
 				super(
 					path_reader: ReadPathAndIPFSSources.new(
@@ -317,7 +325,7 @@ module Dhall
 						public_gateway: ipfs_public_gateway
 					),
 					http_reader: http_reader, https_reader: https_reader,
-					environment_reader: environment_reader
+					environment_reader: environment_reader, max_depth: max_depth
 				)
 			end
 		end
@@ -325,13 +333,15 @@ module Dhall
 		class LocalOnly < Standard
 			def initialize(
 				path_reader: ReadPathSources,
-				environment_reader: ReadEnvironmentSources
+				environment_reader: ReadEnvironmentSources,
+				max_depth: 50
 			)
 				super(
 					path_reader:        path_reader,
 					environment_reader: environment_reader,
 					http_reader:        RejectSources,
-					https_reader:       RejectSources
+					https_reader:       RejectSources,
+					max_depth:          max_depth
 				)
 			end
 		end
diff --git a/test/test_resolve.rb b/test/test_resolve.rb
index 527e2bd..bb52758 100644
--- a/test/test_resolve.rb
+++ b/test/test_resolve.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "base64"
+require "securerandom"
 require "webmock/minitest"
 require "minitest/autorun"
 
@@ -132,6 +133,26 @@ class TestResolve < Minitest::Test
 		)
 	end
 
+	def test_forever_no_loop
+		resolver = Dhall::Resolvers::LocalOnly.new(
+			path_reader: lambda do |sources|
+				sources.map do |_|
+					Promise.resolve(nil).then do
+						"./#{SecureRandom.hex}"
+					end
+				end
+			end
+		)
+
+		assert_raises Dhall::ImportFailedException do
+			Dhall.load(
+				"./start",
+				resolver: resolver,
+				timeout:  Float::INFINITY
+			).sync
+		end
+	end
+
 	def test_missing
 		expr = Dhall::Import.new(
 			Dhall::Import::IntegrityCheck.new,
-- 
2.38.5