From 655d831df763a8366b1c314c901f3b291c2d7b38 Mon Sep 17 00:00:00 2001
From: Kirill Osenkov <github@osenkov.com>
Date: Fri, 29 Oct 2021 15:06:59 -0700
Subject: [PATCH] Protect against circular type forwarders

If we have two assemblies with type forwarders that point to each other, we enter an infinite loop and a stack overflow.

This breaks the cycle by detecting reentrancy.

Fixes https://github.com/jbevain/cecil/issues/706
---
 Mono.Cecil/ExportedType.cs | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Mono.Cecil/ExportedType.cs b/Mono.Cecil/ExportedType.cs
index 8238a0c6d..8b7d00a27 100644
--- a/Mono.Cecil/ExportedType.cs
+++ b/Mono.Cecil/ExportedType.cs
@@ -225,9 +225,21 @@ public override string ToString ()
 			return FullName;
 		}
 
+		private bool reentrancyGuard = false;
+
 		public TypeDefinition Resolve ()
 		{
-			return module.Resolve (CreateReference ());
+			if (reentrancyGuard) {
+				throw new InvalidOperationException ($"Circularity when resolving exported type {this}");
+			}
+
+			reentrancyGuard = true;
+			try {
+				return module.Resolve (CreateReference ());
+			}
+			finally {
+				reentrancyGuard = false;
+			}
 		}
 
 		internal TypeReference CreateReference ()