referrerpolicy=no-referrer-when-downgrade
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
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

use std::{
	collections::{HashMap, HashSet},
	marker::PhantomData,
	sync::Arc,
};

use codec::{Decode, DecodeAll, Encode};
use finality_grandpa::{voter_set::VoterSet, Error as GrandpaError};
use sp_blockchain::{Error as ClientError, HeaderBackend};
use sp_consensus_grandpa::AuthorityId;
use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor};

use crate::{AuthorityList, Commit, Error};

/// A GRANDPA justification for block finality, it includes a commit message and
/// an ancestry proof including all headers routing all precommit target blocks
/// to the commit target block. Due to the current voting strategy the precommit
/// targets should be the same as the commit target, since honest voters don't
/// vote past authority set change blocks.
///
/// This is meant to be stored in the db and passed around the network to other
/// nodes, and are used by syncing nodes to prove authority set handoffs.
#[derive(Clone, Encode, Decode, PartialEq, Eq, Debug)]
pub struct GrandpaJustification<Block: BlockT> {
	/// The GRANDPA justification for block finality.
	pub justification: sp_consensus_grandpa::GrandpaJustification<Block::Header>,
	_block: PhantomData<Block>,
}

impl<Block: BlockT> From<sp_consensus_grandpa::GrandpaJustification<Block::Header>>
	for GrandpaJustification<Block>
{
	fn from(justification: sp_consensus_grandpa::GrandpaJustification<Block::Header>) -> Self {
		Self { justification, _block: Default::default() }
	}
}

impl<Block: BlockT> Into<sp_consensus_grandpa::GrandpaJustification<Block::Header>>
	for GrandpaJustification<Block>
{
	fn into(self) -> sp_consensus_grandpa::GrandpaJustification<Block::Header> {
		self.justification
	}
}

impl<Block: BlockT> GrandpaJustification<Block> {
	/// Create a GRANDPA justification from the given commit. This method
	/// assumes the commit is valid and well-formed.
	pub fn from_commit<C>(
		client: &Arc<C>,
		round: u64,
		commit: Commit<Block::Header>,
	) -> Result<Self, Error>
	where
		C: HeaderBackend<Block>,
	{
		let mut votes_ancestries_hashes = HashSet::new();
		let mut votes_ancestries = Vec::new();

		let error = || {
			let msg = "invalid precommits for target commit".to_string();
			Err(Error::Client(ClientError::BadJustification(msg)))
		};

		// we pick the precommit for the lowest block as the base that
		// should serve as the root block for populating ancestry (i.e.
		// collect all headers from all precommit blocks to the base)
		let (base_hash, base_number) = match commit
			.precommits
			.iter()
			.map(|signed| &signed.precommit)
			.min_by_key(|precommit| precommit.target_number)
			.map(|precommit| (precommit.target_hash, precommit.target_number))
		{
			None => return error(),
			Some(base) => base,
		};

		for signed in commit.precommits.iter() {
			let mut current_hash = signed.precommit.target_hash;
			loop {
				if current_hash == base_hash {
					break
				}

				match client.header(current_hash)? {
					Some(current_header) => {
						// NOTE: this should never happen as we pick the lowest block
						// as base and only traverse backwards from the other blocks
						// in the commit. but better be safe to avoid an unbound loop.
						if *current_header.number() <= base_number {
							return error()
						}

						let parent_hash = *current_header.parent_hash();
						if votes_ancestries_hashes.insert(current_hash) {
							votes_ancestries.push(current_header);
						}

						current_hash = parent_hash;
					},
					_ => return error(),
				}
			}
		}

		Ok(sp_consensus_grandpa::GrandpaJustification { round, commit, votes_ancestries }.into())
	}

	/// Decode a GRANDPA justification and validate the commit and the votes'
	/// ancestry proofs finalize the given block.
	pub fn decode_and_verify_finalizes(
		encoded: &[u8],
		finalized_target: (Block::Hash, NumberFor<Block>),
		set_id: u64,
		voters: &VoterSet<AuthorityId>,
	) -> Result<Self, ClientError>
	where
		NumberFor<Block>: finality_grandpa::BlockNumberOps,
	{
		let justification = GrandpaJustification::<Block>::decode_all(&mut &*encoded)
			.map_err(|_| ClientError::JustificationDecode)?;

		if (
			justification.justification.commit.target_hash,
			justification.justification.commit.target_number,
		) != finalized_target
		{
			let msg = "invalid commit target in grandpa justification".to_string();
			Err(ClientError::BadJustification(msg))
		} else {
			justification.verify_with_voter_set(set_id, voters).map(|_| justification)
		}
	}

	/// Validate the commit and the votes' ancestry proofs.
	pub fn verify(&self, set_id: u64, authorities: &AuthorityList) -> Result<(), ClientError>
	where
		NumberFor<Block>: finality_grandpa::BlockNumberOps,
	{
		let voters = VoterSet::new(authorities.iter().cloned())
			.ok_or(ClientError::Consensus(sp_consensus::Error::InvalidAuthoritiesSet))?;

		self.verify_with_voter_set(set_id, &voters)
	}

	/// Validate the commit and the votes' ancestry proofs.
	pub(crate) fn verify_with_voter_set(
		&self,
		set_id: u64,
		voters: &VoterSet<AuthorityId>,
	) -> Result<(), ClientError>
	where
		NumberFor<Block>: finality_grandpa::BlockNumberOps,
	{
		use finality_grandpa::Chain;

		let ancestry_chain = AncestryChain::<Block>::new(&self.justification.votes_ancestries);

		match finality_grandpa::validate_commit(&self.justification.commit, voters, &ancestry_chain)
		{
			Ok(ref result) if result.is_valid() => {},
			_ => {
				let msg = "invalid commit in grandpa justification".to_string();
				return Err(ClientError::BadJustification(msg))
			},
		}

		// we pick the precommit for the lowest block as the base that
		// should serve as the root block for populating ancestry (i.e.
		// collect all headers from all precommit blocks to the base)
		let base_hash = self
			.justification
			.commit
			.precommits
			.iter()
			.map(|signed| &signed.precommit)
			.min_by_key(|precommit| precommit.target_number)
			.map(|precommit| precommit.target_hash)
			.expect(
				"can only fail if precommits is empty; \
				 commit has been validated above; \
				 valid commits must include precommits; \
				 qed.",
			);

		let mut buf = Vec::new();
		let mut visited_hashes = HashSet::new();
		for signed in self.justification.commit.precommits.iter() {
			if !sp_consensus_grandpa::check_message_signature_with_buffer(
				&finality_grandpa::Message::Precommit(signed.precommit.clone()),
				&signed.id,
				&signed.signature,
				self.justification.round,
				set_id,
				&mut buf,
			) {
				return Err(ClientError::BadJustification(
					"invalid signature for precommit in grandpa justification".to_string(),
				))
			}

			if base_hash == signed.precommit.target_hash {
				continue
			}

			match ancestry_chain.ancestry(base_hash, signed.precommit.target_hash) {
				Ok(route) => {
					// ancestry starts from parent hash but the precommit target hash has been
					// visited
					visited_hashes.insert(signed.precommit.target_hash);
					for hash in route {
						visited_hashes.insert(hash);
					}
				},
				_ =>
					return Err(ClientError::BadJustification(
						"invalid precommit ancestry proof in grandpa justification".to_string(),
					)),
			}
		}

		let ancestry_hashes: HashSet<_> = self
			.justification
			.votes_ancestries
			.iter()
			.map(|h: &Block::Header| h.hash())
			.collect();

		if visited_hashes != ancestry_hashes {
			return Err(ClientError::BadJustification(
				"invalid precommit ancestries in grandpa justification with unused headers"
					.to_string(),
			))
		}

		Ok(())
	}

	/// The target block number and hash that this justifications proves finality for.
	pub fn target(&self) -> (NumberFor<Block>, Block::Hash) {
		(self.justification.commit.target_number, self.justification.commit.target_hash)
	}
}

/// A utility trait implementing `finality_grandpa::Chain` using a given set of headers.
/// This is useful when validating commits, using the given set of headers to
/// verify a valid ancestry route to the target commit block.
struct AncestryChain<Block: BlockT> {
	ancestry: HashMap<Block::Hash, Block::Header>,
}

impl<Block: BlockT> AncestryChain<Block> {
	fn new(ancestry: &[Block::Header]) -> AncestryChain<Block> {
		let ancestry: HashMap<_, _> =
			ancestry.iter().cloned().map(|h: Block::Header| (h.hash(), h)).collect();

		AncestryChain { ancestry }
	}
}

impl<Block: BlockT> finality_grandpa::Chain<Block::Hash, NumberFor<Block>> for AncestryChain<Block>
where
	NumberFor<Block>: finality_grandpa::BlockNumberOps,
{
	fn ancestry(
		&self,
		base: Block::Hash,
		block: Block::Hash,
	) -> Result<Vec<Block::Hash>, GrandpaError> {
		let mut route = Vec::new();
		let mut current_hash = block;
		loop {
			if current_hash == base {
				break
			}
			match self.ancestry.get(&current_hash) {
				Some(current_header) => {
					current_hash = *current_header.parent_hash();
					route.push(current_hash);
				},
				_ => return Err(GrandpaError::NotDescendent),
			}
		}
		route.pop(); // remove the base

		Ok(route)
	}
}