[checkpoints] Detect checkpoint hard fork early (MystenLabs#11003)

This PR detects checkpoints hard fork early in checkpoint builder and
panics validator. This is needed to prevent chain from signing
certificates on the fast path, reducing potential fork impact.

There is some discussion whether panic is the right response in this
case. This PR follows pattern established in the `CheckpointExecutor`
and panics on fork. We can revisit both places in a separate PR if we
want different response in case of a fork.

crates/sui-core/src/checkpoints/mod.rs

@@ -449,6 +449,7 @@ pub struct CheckpointSignatureAggregator {
     summary: CheckpointSummary,
     digest: CheckpointDigest,
     signatures: StakeAggregator<AuthoritySignInfo, true>,
+    failures: StakeAggregator<AuthoritySignInfo, false>,
 }
 
 impl CheckpointBuilder {
@@ -1005,6 +1006,7 @@ impl CheckpointAggregator {
                     digest: summary.digest(),
                     summary,
                     signatures: StakeAggregator::new(self.epoch_store.committee().clone()),
+                    failures: StakeAggregator::new(self.epoch_store.committee().clone()),
                 });
                 self.current.as_mut().unwrap()
             };
@@ -1080,6 +1082,15 @@ impl CheckpointSignatureAggregator {
         let author = signature.authority;
         // consensus ensures that authority == narwhal_cert.author
         if their_digest != self.digest {
+            if let InsertResult::QuorumReached(data) =
+                self.failures.insert_generic(author, signature)
+            {
+                panic!("Checkpoint fork detected - f+1 validators submitted checkpoint digest at seq {} different from our digest {}. Validators with different digests: {:?}",
+                       self.summary.sequence_number,
+                       self.digest,
+                        data.keys()
+                );
+            }
             warn!(
                 "Validator {:?} has mismatching checkpoint digest {} at seq {}, we have digest {}",
                 author.concise(),

crates/sui-core/src/stake_aggregator.rs

@@ -51,7 +51,13 @@ impl<S: Clone + Eq, const STRENGTH: bool> StakeAggregator<S, STRENGTH> {
     /// A generic version of inserting arbitrary type of V (e.g. void type).
     /// If V is AuthoritySignInfo, the `insert` function should be used instead since it does extra
     /// checks and aggregations in the end.
-    pub fn insert_generic(&mut self, authority: AuthorityName, s: S) -> InsertResult<()> {
+    /// Returns Map authority -> S, without aggregating it.
+    /// If you want to get an aggregated signature instead, use `StakeAggregator::insert`
+    pub fn insert_generic(
+        &mut self,
+        authority: AuthorityName,
+        s: S,
+    ) -> InsertResult<&HashMap<AuthorityName, S>> {
         match self.data.entry(authority) {
             Entry::Occupied(oc) => {
                 return InsertResult::Failed {
@@ -69,7 +75,7 @@ impl<S: Clone + Eq, const STRENGTH: bool> StakeAggregator<S, STRENGTH> {
         if votes > 0 {
             self.total_votes += votes;
             if self.total_votes >= self.committee.threshold::<STRENGTH>() {
-                InsertResult::QuorumReached(())
+                InsertResult::QuorumReached(&self.data)
             } else {
                 InsertResult::NotEnoughVotes {
                     bad_votes: 0,