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Auto merge of #60787 - alexcrichton:error-type-id-destabilize-master, r=pietroalbini

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Destabilize the `Error::type_id` function

This commit destabilizes the `Error::type_id` function in the standard library.
This does so by effectively reverting #58048, restoring the `#[unstable]`
attribute. The security mailing list has recently been notified of a
vulnerability relating to the stabilization of this function. First stabilized
in Rust 1.34.0, a stable function here allows users to implement a custom
return value for this function:

    struct MyType;

    impl Error for MyType {
	fn type_id(&self) -> TypeId {
	    // Enable safe casting to `String` by accident.
	    TypeId::of::<String>()
	}
    }

This, when combined with the `Error::downcast` family of functions, allows
safely casting a type to any other type, clearly a memory safety issue! A
formal announcement has been made to the [security mailing list](https://groups.google.com/forum/#!topic/rustlang-security-announcements/aZabeCMUv70) as well as [the blog](https://blog.rust-lang.org/2019/05/13/Security-advisory.html)

This commit simply destabilizes the `Error::type_id` which, although breaking
for users since Rust 1.34.0, is hoped to have little impact and has been deemed
sufficient to mitigate this issue for the stable channel. The long-term fate of
the `Error::type_id` API will be discussed at #60784.
This commit is contained in:
bors 2019-05-14 15:58:33 +00:00
commit f59c71eb8e
2 changed files with 12 additions and 1 deletions
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8
RELEASES.md
View file

@ -1,3 +1,11 @@
Version 1.34.2 (2019-05-14)
===========================
* [Destabilize the `Error::type_id` function due to a security
vulnerability][60785]
[60785]: https://github.com/rust-lang/rust/pull/60785
Version 1.34.1 (2019-04-25)
===========================

5
src/libstd/error.rs
View file

@ -197,7 +197,10 @@ pub trait Error: Debug + Display {
fn source(&self) -> Option<&(dyn Error + 'static)> { None }
/// Gets the `TypeId` of `self`
#[stable(feature = "error_type_id", since = "1.34.0")]
#[doc(hidden)]
#[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 {
TypeId::of::<Self>()
}