Validate encoding of extrinsics passed to runtime (#6442)

* Validate encoding of extrinsics passed to runtime

* Bump codec version explicitly

substrate/primitives/api/src/lib.rs

@@ -69,11 +69,14 @@ pub use sp_std::{slice, mem};
 #[cfg(feature = "std")]
 use sp_std::result;
 #[doc(hidden)]
-pub use codec::{Encode, Decode};
+pub use codec::{Encode, Decode, DecodeLimit};
 use sp_core::OpaqueMetadata;
 #[cfg(feature = "std")]
 use std::{panic::UnwindSafe, cell::RefCell};
 
+/// Maximum nesting level for extrinsics.
+pub const MAX_EXTRINSIC_DEPTH: u32 = 256;
+
 /// Declares given traits as runtime apis.
 ///
 /// The macro will create two declarations, one for using on the client side and one for using