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Correct the prior documented TOCTOU

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Now, if a malicious validator set publishes a malicious `Batch` at the last
moment, it'll cause all future `Batch`s signed by the next validator set to
require a bool being set (yet they never will set it).

This will prevent the handover.

The only overhead is having two distinct `batch_message` calls on-chain.
This commit is contained in:
Luke Parker
2023-10-13 04:40:59 -04:00
parent e6aa9df428
commit d50fe87801
8 changed files with 45 additions and 21 deletions
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24
processor/src/substrate_signer.rs
View File

@@ -52,6 +52,18 @@ impl<D: Db> SubstrateSignerDb<D> {
D::key(b"SUBSTRATE_SIGNER", dst, key)
}
fn first_batch_key(key: [u8; 32]) -> Vec<u8> {
Self::sign_key(b"first_batch", key)
}
fn save_first_batch(txn: &mut D::Transaction<'_>, key: [u8; 32], id: u32) {
txn.put(Self::first_batch_key(key), id.to_le_bytes());
}
fn first_batch<G: Get>(getter: &G, key: [u8; 32]) -> Option<u32> {
getter
.get(Self::first_batch_key(key))
.map(|bytes| u32::from_le_bytes(bytes.try_into().unwrap()))
}
fn completed_key(id: [u8; 32]) -> Vec<u8> {
Self::sign_key(b"completed", id)
}
@@ -229,6 +241,11 @@ impl<D: Db> SubstrateSigner<D> {
return;
}
let group_key = self.keys.group_key().to_bytes();
if SubstrateSignerDb::<D>::first_batch(txn, group_key).is_none() {
SubstrateSignerDb::<D>::save_first_batch(txn, group_key, batch.id);
}
self.signable.insert(id, batch);
self.attempt(txn, id, 0).await;
}
@@ -270,8 +287,13 @@ impl<D: Db> SubstrateSigner<D> {
Err(e) => todo!("malicious signer: {:?}", e),
};
let batch = &self.signable[&id.id];
let is_first_batch =
SubstrateSignerDb::<D>::first_batch(txn, self.keys.group_key().to_bytes()).unwrap() ==
batch.id;
let (machine, share) =
match machine.sign(preprocesses, &batch_message(&self.signable[&id.id])) {
match machine.sign(preprocesses, &batch_message(is_first_batch, batch)) {
Ok(res) => res,
Err(e) => todo!("malicious signer: {:?}", e),
};

3
processor/src/tests/substrate_signer.rs
View File

@@ -146,8 +146,9 @@ async fn test_substrate_signer() {
signers.get_mut(i).unwrap().events.pop_front().unwrap()
{
assert_eq!(signed_batch.batch, batch);
// SubstrateSigner will believe this is the first batch for this set, hence `true`
assert!(Public::from_raw(keys[&participant_one].group_key().to_bytes())
.verify(&batch_message(&batch), &signed_batch.signature));
.verify(&batch_message(true, &batch), &signed_batch.signature));
} else {
panic!("didn't get signed batch back");
}