1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! An opt-in utility module for reporting equivocations.
//!
//! This module defines an offence type for GRANDPA equivocations
//! and some utility traits to wire together:
//! - a key ownership proof system (e.g. to prove that a given authority was
//! part of a session);
//! - a system for reporting offences;
//! - a system for signing and submitting transactions;
//! - a way to get the current block author;
//!
//! These can be used in an offchain context in order to submit equivocation
//! reporting extrinsics (from the client that's running the GRANDPA protocol).
//! And in a runtime context, so that the GRANDPA module can validate the
//! equivocation proofs in the extrinsic and report the offences.
//!
//! IMPORTANT:
//! When using this module for enabling equivocation reporting it is required
//! that the `ValidateUnsigned` for the GRANDPA pallet is used in the runtime
//! definition.

use alloc::{boxed::Box, vec, vec::Vec};
use codec::{self as codec, Decode, Encode};
use frame_support::traits::{Get, KeyOwnerProofSystem};
use frame_system::pallet_prelude::BlockNumberFor;
use log::{error, info};
use sp_consensus_grandpa::{AuthorityId, EquivocationProof, RoundNumber, SetId, KEY_TYPE};
use sp_runtime::{
	transaction_validity::{
		InvalidTransaction, TransactionPriority, TransactionSource, TransactionValidity,
		TransactionValidityError, ValidTransaction,
	},
	DispatchError, KeyTypeId, Perbill,
};
use sp_session::{GetSessionNumber, GetValidatorCount};
use sp_staking::{
	offence::{Kind, Offence, OffenceReportSystem, ReportOffence},
	SessionIndex,
};

use super::{Call, Config, Error, Pallet, LOG_TARGET};

/// A round number and set id which point on the time of an offence.
#[derive(Copy, Clone, PartialOrd, Ord, Eq, PartialEq, Encode, Decode)]
pub struct TimeSlot {
	// The order of these matters for `derive(Ord)`.
	/// Grandpa Set ID.
	pub set_id: SetId,
	/// Round number.
	pub round: RoundNumber,
}

/// GRANDPA equivocation offence report.
pub struct EquivocationOffence<Offender> {
	/// Time slot at which this incident happened.
	pub time_slot: TimeSlot,
	/// The session index in which the incident happened.
	pub session_index: SessionIndex,
	/// The size of the validator set at the time of the offence.
	pub validator_set_count: u32,
	/// The authority which produced this equivocation.
	pub offender: Offender,
}

impl<Offender: Clone> Offence<Offender> for EquivocationOffence<Offender> {
	const ID: Kind = *b"grandpa:equivoca";
	type TimeSlot = TimeSlot;

	fn offenders(&self) -> Vec<Offender> {
		vec![self.offender.clone()]
	}

	fn session_index(&self) -> SessionIndex {
		self.session_index
	}

	fn validator_set_count(&self) -> u32 {
		self.validator_set_count
	}

	fn time_slot(&self) -> Self::TimeSlot {
		self.time_slot
	}

	// The formula is min((3k / n)^2, 1)
	// where k = offenders_number and n = validators_number
	fn slash_fraction(&self, offenders_count: u32) -> Perbill {
		// Perbill type domain is [0, 1] by definition
		Perbill::from_rational(3 * offenders_count, self.validator_set_count).square()
	}
}

/// GRANDPA equivocation offence report system.
///
/// This type implements `OffenceReportSystem` such that:
/// - Equivocation reports are published on-chain as unsigned extrinsic via
///   `offchain::SendTransactionTypes`.
/// - On-chain validity checks and processing are mostly delegated to the user provided generic
///   types implementing `KeyOwnerProofSystem` and `ReportOffence` traits.
/// - Offence reporter for unsigned transactions is fetched via the the authorship pallet.
pub struct EquivocationReportSystem<T, R, P, L>(core::marker::PhantomData<(T, R, P, L)>);

impl<T, R, P, L>
	OffenceReportSystem<
		Option<T::AccountId>,
		(EquivocationProof<T::Hash, BlockNumberFor<T>>, T::KeyOwnerProof),
	> for EquivocationReportSystem<T, R, P, L>
where
	T: Config + pallet_authorship::Config + frame_system::offchain::SendTransactionTypes<Call<T>>,
	R: ReportOffence<
		T::AccountId,
		P::IdentificationTuple,
		EquivocationOffence<P::IdentificationTuple>,
	>,
	P: KeyOwnerProofSystem<(KeyTypeId, AuthorityId), Proof = T::KeyOwnerProof>,
	P::IdentificationTuple: Clone,
	L: Get<u64>,
{
	type Longevity = L;

	fn publish_evidence(
		evidence: (EquivocationProof<T::Hash, BlockNumberFor<T>>, T::KeyOwnerProof),
	) -> Result<(), ()> {
		use frame_system::offchain::SubmitTransaction;
		let (equivocation_proof, key_owner_proof) = evidence;

		let call = Call::report_equivocation_unsigned {
			equivocation_proof: Box::new(equivocation_proof),
			key_owner_proof,
		};
		let res = SubmitTransaction::<T, Call<T>>::submit_unsigned_transaction(call.into());
		match res {
			Ok(_) => info!(target: LOG_TARGET, "Submitted equivocation report"),
			Err(e) => error!(target: LOG_TARGET, "Error submitting equivocation report: {:?}", e),
		}
		res
	}

	fn check_evidence(
		evidence: (EquivocationProof<T::Hash, BlockNumberFor<T>>, T::KeyOwnerProof),
	) -> Result<(), TransactionValidityError> {
		let (equivocation_proof, key_owner_proof) = evidence;

		// Check the membership proof to extract the offender's id
		let key = (KEY_TYPE, equivocation_proof.offender().clone());
		let offender = P::check_proof(key, key_owner_proof).ok_or(InvalidTransaction::BadProof)?;

		// Check if the offence has already been reported, and if so then we can discard the report.
		let time_slot =
			TimeSlot { set_id: equivocation_proof.set_id(), round: equivocation_proof.round() };
		if R::is_known_offence(&[offender], &time_slot) {
			Err(InvalidTransaction::Stale.into())
		} else {
			Ok(())
		}
	}

	fn process_evidence(
		reporter: Option<T::AccountId>,
		evidence: (EquivocationProof<T::Hash, BlockNumberFor<T>>, T::KeyOwnerProof),
	) -> Result<(), DispatchError> {
		let (equivocation_proof, key_owner_proof) = evidence;
		let reporter = reporter.or_else(|| <pallet_authorship::Pallet<T>>::author());
		let offender = equivocation_proof.offender().clone();

		// We check the equivocation within the context of its set id (and
		// associated session) and round. We also need to know the validator
		// set count when the offence since it is required to calculate the
		// slash amount.
		let set_id = equivocation_proof.set_id();
		let round = equivocation_proof.round();
		let session_index = key_owner_proof.session();
		let validator_set_count = key_owner_proof.validator_count();

		// Validate equivocation proof (check votes are different and signatures are valid).
		if !sp_consensus_grandpa::check_equivocation_proof(equivocation_proof) {
			return Err(Error::<T>::InvalidEquivocationProof.into())
		}

		// Validate the key ownership proof extracting the id of the offender.
		let offender = P::check_proof((KEY_TYPE, offender), key_owner_proof)
			.ok_or(Error::<T>::InvalidKeyOwnershipProof)?;

		// Fetch the current and previous sets last session index.
		// For genesis set there's no previous set.
		let previous_set_id_session_index = if set_id != 0 {
			let idx = crate::SetIdSession::<T>::get(set_id - 1)
				.ok_or(Error::<T>::InvalidEquivocationProof)?;
			Some(idx)
		} else {
			None
		};

		let set_id_session_index =
			crate::SetIdSession::<T>::get(set_id).ok_or(Error::<T>::InvalidEquivocationProof)?;

		// Check that the session id for the membership proof is within the
		// bounds of the set id reported in the equivocation.
		if session_index > set_id_session_index ||
			previous_set_id_session_index
				.map(|previous_index| session_index <= previous_index)
				.unwrap_or(false)
		{
			return Err(Error::<T>::InvalidEquivocationProof.into())
		}

		let offence = EquivocationOffence {
			time_slot: TimeSlot { set_id, round },
			session_index,
			offender,
			validator_set_count,
		};

		R::report_offence(reporter.into_iter().collect(), offence)
			.map_err(|_| Error::<T>::DuplicateOffenceReport)?;

		Ok(())
	}
}

/// Methods for the `ValidateUnsigned` implementation:
/// It restricts calls to `report_equivocation_unsigned` to local calls (i.e. extrinsics generated
/// on this node) or that already in a block. This guarantees that only block authors can include
/// unsigned equivocation reports.
impl<T: Config> Pallet<T> {
	pub fn validate_unsigned(source: TransactionSource, call: &Call<T>) -> TransactionValidity {
		if let Call::report_equivocation_unsigned { equivocation_proof, key_owner_proof } = call {
			// discard equivocation report not coming from the local node
			match source {
				TransactionSource::Local | TransactionSource::InBlock => { /* allowed */ },
				_ => {
					log::warn!(
						target: LOG_TARGET,
						"rejecting unsigned report equivocation transaction because it is not local/in-block."
					);

					return InvalidTransaction::Call.into()
				},
			}

			// Check report validity
			let evidence = (*equivocation_proof.clone(), key_owner_proof.clone());
			T::EquivocationReportSystem::check_evidence(evidence)?;

			let longevity =
				<T::EquivocationReportSystem as OffenceReportSystem<_, _>>::Longevity::get();

			ValidTransaction::with_tag_prefix("GrandpaEquivocation")
				// We assign the maximum priority for any equivocation report.
				.priority(TransactionPriority::max_value())
				// Only one equivocation report for the same offender at the same slot.
				.and_provides((
					equivocation_proof.offender().clone(),
					equivocation_proof.set_id(),
					equivocation_proof.round(),
				))
				.longevity(longevity)
				// We don't propagate this. This can never be included on a remote node.
				.propagate(false)
				.build()
		} else {
			InvalidTransaction::Call.into()
		}
	}

	pub fn pre_dispatch(call: &Call<T>) -> Result<(), TransactionValidityError> {
		if let Call::report_equivocation_unsigned { equivocation_proof, key_owner_proof } = call {
			let evidence = (*equivocation_proof.clone(), key_owner_proof.clone());
			T::EquivocationReportSystem::check_evidence(evidence)
		} else {
			Err(InvalidTransaction::Call.into())
		}
	}
}