Merge branch 'master' into backport-tests-for-claim-assets

polkadot/roadmap/implementers-guide/src/node/backing/candidate-backing.md

@@ -1,5 +1,9 @@
 # Candidate Backing
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 The Candidate Backing subsystem ensures every parablock considered for relay block inclusion has been seconded by at
 least one validator, and approved by a quorum. Parablocks for which not enough validators will assert correctness are
 discarded. If the block later proves invalid, the initial backers are slashable; this gives Polkadot a rational threat

polkadot/roadmap/implementers-guide/src/node/backing/prospective-parachains.md

@@ -1,5 +1,9 @@
 # Prospective Parachains
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 ## Overview
 
 **Purpose:** Tracks and handles prospective parachain fragments and informs

polkadot/roadmap/implementers-guide/src/node/collators/collator-protocol.md

@@ -1,5 +1,9 @@
 # Collator Protocol
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 The Collator Protocol implements the network protocol by which collators and validators communicate. It is used by
 collators to distribute collations to validators and used by validators to accept collations by collators.
 

polkadot/roadmap/implementers-guide/src/node/utility/provisioner.md

@@ -1,5 +1,9 @@
 # Provisioner
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 Relay chain block authorship authority is governed by BABE and is beyond the scope of the Overseer and the rest of the
 subsystems. That said, ultimately the block author needs to select a set of backable parachain candidates and other
 consensus data, and assemble a block from them. This subsystem is responsible for providing the necessary data to all

polkadot/roadmap/implementers-guide/src/runtime/inclusion.md

@@ -1,5 +1,9 @@
 # Inclusion Pallet
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 The inclusion module is responsible for inclusion and availability of scheduled parachains. It also manages the UMP
 dispatch queue of each parachain.
 

polkadot/roadmap/implementers-guide/src/runtime/parainherent.md

@@ -1,5 +1,9 @@
 # `ParaInherent`
 
+> NOTE: This module has suffered changes for the elastic scaling implementation. As a result, parts of this document may
+be out of date and will be updated at a later time. Issue tracking the update:
+https://github.com/paritytech/polkadot-sdk/issues/3699
+
 This module is responsible for providing all data given to the runtime by the block author to the various parachains
 modules. The entry-point is mandatory, in that it must be invoked exactly once within every block, and it is also
 "inherent", in that it is provided with no origin by the block author. The data within it carries its own

polkadot/xcm/src/v2/mod.rs

@@ -62,7 +62,10 @@ use super::{
 };
 use alloc::{vec, vec::Vec};
 use bounded_collections::{ConstU32, WeakBoundedVec};
-use codec::{self, Decode, Encode, MaxEncodedLen};
+use codec::{
+	self, decode_vec_with_len, Compact, Decode, Encode, Error as CodecError, Input as CodecInput,
+	MaxEncodedLen,
+};
 use core::{fmt::Debug, result};
 use derivative::Derivative;
 use scale_info::TypeInfo;
@@ -278,14 +281,39 @@ pub const VERSION: super::Version = 2;
 pub type QueryId = u64;
 
 /// DEPRECATED. Please use XCMv3 or XCMv4 instead.
-#[derive(Derivative, Default, Encode, Decode, TypeInfo)]
+#[derive(Derivative, Default, Encode, TypeInfo)]
 #[derivative(Clone(bound = ""), Eq(bound = ""), PartialEq(bound = ""), Debug(bound = ""))]
 #[codec(encode_bound())]
 #[codec(decode_bound())]
 #[scale_info(bounds(), skip_type_params(RuntimeCall))]
 #[scale_info(replace_segment("staging_xcm", "xcm"))]
 pub struct Xcm<RuntimeCall>(pub Vec<Instruction<RuntimeCall>>);
 
+environmental::environmental!(instructions_count: u8);
+
+impl<Call> Decode for Xcm<Call> {
+	fn decode<I: CodecInput>(input: &mut I) -> core::result::Result<Self, CodecError> {
+		instructions_count::using_once(&mut 0, || {
+			let number_of_instructions: u32 = <Compact<u32>>::decode(input)?.into();
+			instructions_count::with(|count| {
+				*count = count.saturating_add(number_of_instructions as u8);
+				if *count > MAX_INSTRUCTIONS_TO_DECODE {
+					return Err(CodecError::from("Max instructions exceeded"))
+				}
+				Ok(())
+			})
+			.unwrap_or(Ok(()))?;
+			let decoded_instructions = decode_vec_with_len(input, number_of_instructions as usize)?;
+			Ok(Self(decoded_instructions))
+		})
+	}
+}
+
+/// The maximal number of instructions in an XCM before decoding fails.
+///
+/// This is a deliberate limit - not a technical one.
+pub const MAX_INSTRUCTIONS_TO_DECODE: u8 = 100;
+
 impl<RuntimeCall> Xcm<RuntimeCall> {
 	/// Create an empty instance.
 	pub fn new() -> Self {
@@ -1157,3 +1185,38 @@ impl<RuntimeCall> TryFrom<NewInstruction<RuntimeCall>> for Instruction<RuntimeCa
 		})
 	}
 }
+
+#[cfg(test)]
+mod tests {
+	use super::{prelude::*, *};
+
+	#[test]
+	fn decoding_respects_limit() {
+		let max_xcm = Xcm::<()>(vec![ClearOrigin; MAX_INSTRUCTIONS_TO_DECODE as usize]);
+		let encoded = max_xcm.encode();
+		assert!(Xcm::<()>::decode(&mut &encoded[..]).is_ok());
+
+		let big_xcm = Xcm::<()>(vec![ClearOrigin; MAX_INSTRUCTIONS_TO_DECODE as usize + 1]);
+		let encoded = big_xcm.encode();
+		assert!(Xcm::<()>::decode(&mut &encoded[..]).is_err());
+
+		let nested_xcm = Xcm::<()>(vec![
+			DepositReserveAsset {
+				assets: All.into(),
+				dest: Here.into(),
+				xcm: max_xcm,
+				max_assets: 1,
+			};
+			(MAX_INSTRUCTIONS_TO_DECODE / 2) as usize
+		]);
+		let encoded = nested_xcm.encode();
+		assert!(Xcm::<()>::decode(&mut &encoded[..]).is_err());
+
+		let even_more_nested_xcm = Xcm::<()>(vec![SetAppendix(nested_xcm); 64]);
+		let encoded = even_more_nested_xcm.encode();
+		assert_eq!(encoded.len(), 345730);
+		// This should not decode since the limit is 100
+		assert_eq!(MAX_INSTRUCTIONS_TO_DECODE, 100, "precondition");
+		assert!(Xcm::<()>::decode(&mut &encoded[..]).is_err());
+	}
+}

prdoc/pr_4978.prdoc

@@ -0,0 +1,18 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Add MAX_INSTRUCTIONS_TO_DECODE to XCMv2
+
+doc:
+  - audience: Runtime User
+    description: |
+      Added a max number of instructions to XCMv2. If using XCMv2, you'll have to take this limit into account.
+      It was set to 100.
+  - audience: Runtime Dev
+    description: |
+      Added a max number of instructions to XCMv2. If using XCMv2, you'll have to take this limit into account.
+      It was set to 100.
+
+crates:
+  - name: staging-xcm
+    bump: minor