From e836a4cd79c8b7f6ba8ea93c6da29e7b803116f3 Mon Sep 17 00:00:00 2001 From: Steven Fackler Date: Thu, 16 May 2019 19:48:13 -0700 Subject: [PATCH] Prevent Error::type_id overrides type_id now takes an argument that can't be named outside of the std::error module, which prevents any implementations from overriding it. It's a pretty grody solution, and there's no way we can stabilize the method with this API, but it avoids the soudness issue! Closes #60784 --- src/libstd/error.rs | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/src/libstd/error.rs b/src/libstd/error.rs index 7cb830e751a..d2aa2195a35 100644 --- a/src/libstd/error.rs +++ b/src/libstd/error.rs @@ -201,11 +201,19 @@ pub trait Error: Debug + Display { #[unstable(feature = "error_type_id", reason = "this is memory unsafe to override in user code", issue = "60784")] - fn type_id(&self) -> TypeId where Self: 'static { + fn type_id(&self, _: private::Internal) -> TypeId where Self: 'static { TypeId::of::() } } +mod private { + // this is a hack to prevent type_id from being overridden by Error + // implementations, since that can enable unsound downcasting. + #[unstable(feature = "error_type_id", issue = "60784")] + #[derive(Debug)] + pub struct Internal; +} + #[stable(feature = "rust1", since = "1.0.0")] impl<'a, E: Error + 'a> From for Box { /// Converts a type of [`Error`] into a box of dyn [`Error`]. @@ -575,7 +583,7 @@ impl dyn Error + 'static { let t = TypeId::of::(); // Get TypeId of the type in the trait object - let boxed = self.type_id(); + let boxed = self.type_id(private::Internal); // Compare both TypeIds on equality t == boxed