Prevent block times from ever going backward

core/src/rpc.rs

@@ -2703,7 +2703,6 @@ pub mod tests {
         message::Message,
         nonce, rpc_port,
         signature::{Keypair, Signer},
-        stake_weighted_timestamp::EstimateType,
         system_program, system_transaction,
         timing::slot_duration_from_slots_per_year,
         transaction::{self, TransactionError},

runtime/src/bank.rs

@@ -1114,7 +1114,16 @@ impl Bank {
                         ("from_genesis", unix_timestamp, i64),
                         ("corrected", timestamp_estimate, i64),
                     );
-                    unix_timestamp = timestamp_estimate
+                    unix_timestamp = timestamp_estimate;
+
+                    let ancestor_timestamp = self.clock().unix_timestamp;
+                    if self
+                        .feature_set
+                        .is_active(&feature_set::timestamp_bounding::id())
+                        && timestamp_estimate < ancestor_timestamp
+                    {
+                        unix_timestamp = ancestor_timestamp;
+                    }
                 }
             }
         }
@@ -9924,7 +9933,7 @@ mod tests {
             voting_keypair,
             ..
         } = create_genesis_config_with_leader(5, &leader_pubkey, 3);
-        let bank = Bank::new(&genesis_config);
+        let mut bank = Bank::new(&genesis_config);
         assert_eq!(
             bank.clock().unix_timestamp,
             bank.unix_timestamp_from_genesis()
@@ -9977,6 +9986,22 @@ mod tests {
             bank.clock().unix_timestamp,
             bank.unix_timestamp_from_genesis() + 1
         );
+
+        // Timestamp cannot go backward from ancestor Bank to child
+        bank = new_from_parent(&Arc::new(bank));
+        update_vote_account_timestamp(
+            BlockTimestamp {
+                slot: bank.slot(),
+                timestamp: bank.unix_timestamp_from_genesis() - 1,
+            },
+            &bank,
+            &voting_keypair.pubkey(),
+        );
+        bank.update_clock(None);
+        assert_eq!(
+            bank.clock().unix_timestamp,
+            bank.unix_timestamp_from_genesis()
+        );
     }
 
     fn setup_bank_with_removable_zero_lamport_account() -> Arc<Bank> {