fix(p2p): include previous block hash when calculating signatures (#1336)

* Fix

* Empty

* Remove default value

* No optional values

* style: resolve style guide violations [ci-lint-fix]

Author: sebastijankuzner

packages/consensus/source/processors/commit-processor.ts

@@ -37,7 +37,7 @@ export class CommitProcessor extends AbstractProcessor implements Contracts.Cons
 			: Enums.Consensus.ProcessorResult.Invalid;
 	}
 
-	async hasValidSignature(commit: Contracts.Crypto.Commit): Promise<boolean> {
+	async hasValidSignature(commit: Contracts.Crypto.Commit, previousBlockHash: string): Promise<boolean> {
 		const { block, proof } = commit;
 
 		const publicKeys: Buffer[] = [];
@@ -64,7 +64,7 @@ export class CommitProcessor extends AbstractProcessor implements Contracts.Cons
 			},
 			{
 				genesisBlockHash: this.stateStore.getGenesisCommit().block.hash,
-				previousBlockHash: this.stateStore.getLastBlock().hash,
+				previousBlockHash,
 			},
 		);
 

packages/contracts/source/contracts/consensus/processor.ts

@@ -12,5 +12,5 @@ export interface MessageProcessor {
 
 export interface CommitProcessor {
 	process(commit: Commit, broadcast?: boolean): Promise<ProcessorResult>;
-	hasValidSignature(commit: Commit): Promise<boolean>;
+	hasValidSignature(commit: Commit, previousBlockHash: string): Promise<boolean>;
 }

packages/p2p/source/downloader/block-downloader.ts

@@ -159,8 +159,15 @@ export class BlockDownloader implements Contracts.P2P.Downloader {
 					}
 				}
 
+				// Each commit's precommit signature covers the previous block hash, so verify
+				// against the actual predecessor in the chain instead of the store's last block
+				// (which is stale for every commit but the first until the batch is processed).
 				const hasValidSignatures = await Promise.all(
-					commits.map(async (commit) => await this.commitProcessor.hasValidSignature(commit)),
+					commits.map(async (commit, index) =>
+						index === 0
+							? await this.commitProcessor.hasValidSignature(commit, this.stateStore.getLastBlock().hash)
+							: await this.commitProcessor.hasValidSignature(commit, commits[index - 1].block.hash),
+					),
 				);
 
 				if (!hasValidSignatures.every(Boolean)) {