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Prevent a malicious validator set from overwriting a notable cosign

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Also prevents panics from an invalid Serai node (removing the assumption of an
honest Serai node).
This commit is contained in:
Luke Parker
2024-12-25 02:11:05 -05:00
parent e119fb4c16
commit 5b337c3ce8
3 changed files with 40 additions and 34 deletions
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41
coordinator/cosign/src/lib.rs
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@@ -62,6 +62,8 @@ create_db! {
Cosign {
// A mapping from a global session's ID to its start block (number, hash).
GlobalSessions: (global_session: [u8; 32]) -> (u64, [u8; 32]),
// The last block to be cosigned by a global session.
GlobalSessionLastBlock: (global_session: [u8; 32]) -> u64,
// The latest global session intended.
//
// This is distinct from the latest global session for which we've evaluated the cosigns for.
@@ -295,7 +297,7 @@ impl<D: Db> Cosigning<D> {
/// cosigns, in case of a fault, to induce identification of the fault by others.
pub fn cosigns_to_rebroadcast(&self) -> Vec<SignedCosign> {
if let Some(faulted) = FaultedSession::get(&self.db) {
let mut cosigns = Faults::get(&self.db, faulted).unwrap();
let mut cosigns = Faults::get(&self.db, faulted).expect("faulted with no faults");
// Also include all of our recognized-as-honest cosigns in an attempt to induce fault
// identification in those who see the faulty cosigns as honest
for network in serai_client::primitives::NETWORKS {
@@ -345,19 +347,22 @@ impl<D: Db> Cosigning<D> {
return Ok(false);
};
// Check if we should even bother handling this cosign
let mut txn = self.db.txn();
// TODO: A malicious validator set can sign a block after their notable block to erase a
// notable cosign
if let Some(existing) = NetworksLatestCosignedBlock::get(&txn, cosign.global_session, network) {
// Check this isn't a dated cosign
if let Some(existing) =
NetworksLatestCosignedBlock::get(&self.db, cosign.global_session, network)
{
if existing.cosign.block_number >= cosign.block_number {
return Ok(true);
}
}
// Check we can verify this cosign's signature
// Check our finalized (and indexed by intend) blockchain exceeds this block number
if cosign.block_number >= intend::ScanCosignFrom::get(&self.db).unwrap_or(0) {
return Ok(true);
}
let Some((global_session_start_block_number, global_session_start_block_hash)) =
GlobalSessions::get(&txn, cosign.global_session)
GlobalSessions::get(&self.db, cosign.global_session)
else {
// Unrecognized global session
return Ok(true);
@@ -366,6 +371,10 @@ impl<D: Db> Cosigning<D> {
// Cosign is for a block predating the global session
return Ok(false);
}
if Some(cosign.block_number) > GlobalSessionLastBlock::get(&self.db, cosign.global_session) {
// Cosign is for a block after the last block this global session should have signed
return Ok(false);
}
// Check the cosign's signature
{
@@ -388,23 +397,17 @@ impl<D: Db> Cosigning<D> {
}
}
// Check our finalized blockchain exceeds this block number
if self.serai.latest_finalized_block().await.map_err(|e| format!("{e:?}"))?.number() <
cosign.block_number
{
// Unrecognized block number
return Ok(true);
}
// Since we verified this cosign's signature, and have a chain sufficiently long, handle the
// cosign
let mut txn = self.db.txn();
let our_block_hash = self
.serai
.block_hash(cosign.block_number)
.await
.map_err(|e| format!("{e:?}"))?
.expect("requested hash of a finalized block yet received None");
.ok_or_else(|| "requested hash of a finalized block yet received None".to_string())?;
if our_block_hash == cosign.block_hash {
// If this is for a future global session, we don't acknowledge this cosign at this time
if global_session_start_block_number > LatestCosignedBlockNumber::get(&txn).unwrap_or(0) {
@@ -445,10 +448,6 @@ impl<D: Db> Cosigning<D> {
}
// Check if the sum weight means a fault has occurred
assert!(
total_weight != 0,
"evaluating valid cosign when no stake was present in the system"
);
if weight_cosigned >= ((total_weight * 17) / 100) {
FaultedSession::set(&mut txn, &cosign.global_session);
}