Limit number of uncles that can be provided. (#4298)

* Limit number of uncles that can be provided.

* Check length of uncles vector on inherent.

* Set fatal error to true for too many uncles.

* Take max uncles in create_inherent.

substrate/primitives/authorship/src/lib.rs

@@ -21,11 +21,27 @@
 use rstd::{result::Result, prelude::*};
 
 use codec::{Encode, Decode};
-use sp_inherents::{Error, InherentIdentifier, InherentData};
+use sp_inherents::{Error, InherentIdentifier, InherentData, IsFatalError};
+use sr_primitives::RuntimeString;
 
 /// The identifier for the `uncles` inherent.
 pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"uncles00";
 
+/// Errors that can occur while checking the authorship inherent.
+#[derive(Encode, sr_primitives::RuntimeDebug)]
+#[cfg_attr(feature = "std", derive(Decode))]
+pub enum InherentError {
+	Uncles(RuntimeString),
+}
+
+impl IsFatalError for InherentError {
+	fn is_fatal_error(&self) -> bool {
+		match self {
+			InherentError::Uncles(_) => true,
+		}
+	}
+}
+
 /// Auxiliary trait to extract uncles inherent data.
 pub trait UnclesInherentData<H: Decode> {
 	/// Get uncles.