Detect invalid proposer signature on RPC block processing (#6519)

Complements
- https://github.com/sigp/lighthouse/pull/6321

by detecting if the proposer signature is valid or not during RPC block processing. In lookup sync, if the invalid signature signature is the proposer signature, it's not deterministic on the block root. So we should only penalize the sending peer and retry. Otherwise, if it's on the body we should drop the lookup and penalize all peers that claim to have imported the block

beacon_node/beacon_chain/src/block_verification.rs

@@ -208,24 +208,18 @@ pub enum BlockError {
     ///
     /// The block is invalid and the peer is faulty.
     IncorrectBlockProposer { block: u64, local_shuffling: u64 },
-    /// The proposal signature in invalid.
-    ///
-    /// ## Peer scoring
-    ///
-    /// The block is invalid and the peer is faulty.
-    ProposalSignatureInvalid,
     /// The `block.proposal_index` is not known.
     ///
     /// ## Peer scoring
     ///
     /// The block is invalid and the peer is faulty.
     UnknownValidator(u64),
-    /// A signature in the block is invalid (exactly which is unknown).
+    /// A signature in the block is invalid
     ///
     /// ## Peer scoring
     ///
     /// The block is invalid and the peer is faulty.
-    InvalidSignature,
+    InvalidSignature(InvalidSignature),
     /// The provided block is not from a later slot than its parent.
     ///
     /// ## Peer scoring
@@ -329,6 +323,17 @@ pub enum BlockError {
     InternalError(String),
 }
 
+/// Which specific signature(s) are invalid in a SignedBeaconBlock
+#[derive(Debug)]
+pub enum InvalidSignature {
+    // The outer signature in a SignedBeaconBlock
+    ProposerSignature,
+    // One or more signatures in BeaconBlockBody
+    BlockBodySignatures,
+    // One or more signatures in SignedBeaconBlock
+    Unknown,
+}
+
 impl From<AvailabilityCheckError> for BlockError {
     fn from(e: AvailabilityCheckError) -> Self {
         Self::AvailabilityCheck(e)
@@ -523,7 +528,9 @@ pub enum BlockSlashInfo<TErr> {
 impl BlockSlashInfo<BlockError> {
     pub fn from_early_error_block(header: SignedBeaconBlockHeader, e: BlockError) -> Self {
         match e {
-            BlockError::ProposalSignatureInvalid => BlockSlashInfo::SignatureInvalid(e),
+            BlockError::InvalidSignature(InvalidSignature::ProposerSignature) => {
+                BlockSlashInfo::SignatureInvalid(e)
+            }
             // `InvalidSignature` could indicate any signature in the block, so we want
             // to recheck the proposer signature alone.
             _ => BlockSlashInfo::SignatureNotChecked(header, e),
@@ -652,7 +659,7 @@ pub fn signature_verify_chain_segment<T: BeaconChainTypes>(
     }
 
     if signature_verifier.verify().is_err() {
-        return Err(BlockError::InvalidSignature);
+        return Err(BlockError::InvalidSignature(InvalidSignature::Unknown));
     }
 
     drop(pubkey_cache);
@@ -964,7 +971,9 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
         };
 
         if !signature_is_valid {
-            return Err(BlockError::ProposalSignatureInvalid);
+            return Err(BlockError::InvalidSignature(
+                InvalidSignature::ProposerSignature,
+            ));
         }
 
         chain
@@ -1098,7 +1107,26 @@ impl<T: BeaconChainTypes> SignatureVerifiedBlock<T> {
                 parent: Some(parent),
             })
         } else {
-            Err(BlockError::InvalidSignature)
+            // Re-verify the proposer signature in isolation to attribute fault
+            let pubkey = pubkey_cache
+                .get(block.message().proposer_index() as usize)
+                .ok_or_else(|| BlockError::UnknownValidator(block.message().proposer_index()))?;
+            if block.as_block().verify_signature(
+                Some(block_root),
+                pubkey,
+                &state.fork(),
+                chain.genesis_validators_root,
+                &chain.spec,
+            ) {
+                // Proposer signature is valid, the invalid signature must be in the body
+                Err(BlockError::InvalidSignature(
+                    InvalidSignature::BlockBodySignatures,
+                ))
+            } else {
+                Err(BlockError::InvalidSignature(
+                    InvalidSignature::ProposerSignature,
+                ))
+            }
         }
     }
 
@@ -1153,7 +1181,9 @@ impl<T: BeaconChainTypes> SignatureVerifiedBlock<T> {
                 consensus_context,
             })
         } else {
-            Err(BlockError::InvalidSignature)
+            Err(BlockError::InvalidSignature(
+                InvalidSignature::BlockBodySignatures,
+            ))
         }
     }
 
@@ -1981,7 +2011,7 @@ impl BlockBlobError for BlockError {
     }
 
     fn proposer_signature_invalid() -> Self {
-        BlockError::ProposalSignatureInvalid
+        BlockError::InvalidSignature(InvalidSignature::ProposerSignature)
     }
 }
 

beacon_node/beacon_chain/src/lib.rs

@@ -78,7 +78,7 @@ pub use beacon_fork_choice_store::{BeaconForkChoiceStore, Error as ForkChoiceSto
 pub use block_verification::{
     build_blob_data_column_sidecars, get_block_root, BlockError, ExecutionPayloadError,
     ExecutionPendingBlock, GossipVerifiedBlock, IntoExecutionPendingBlock, IntoGossipVerifiedBlock,
-    PayloadVerificationOutcome, PayloadVerificationStatus,
+    InvalidSignature, PayloadVerificationOutcome, PayloadVerificationStatus,
 };
 pub use block_verification_types::AvailabilityPendingExecutedBlock;
 pub use block_verification_types::ExecutedBlock;