Rehashing is not allowed to change accounts (#3180)

runtime/src/bank.rs

@@ -2869,11 +2869,34 @@ impl Bank {
         stake_weighted_timestamp
     }
 
+    /// Recalculates the bank hash
+    ///
+    /// This is used by ledger-tool when creating a snapshot, which
+    /// recalcuates the bank hash.
+    ///
+    /// Note that the account state is *not* allowed to change by rehashing.
+    /// If it does, this function will panic.
+    /// If modifying accounts in ledger-tool is needed, create a new bank.
     pub fn rehash(&self) {
+        let get_delta_hash = || {
+            self.rc
+                .accounts
+                .accounts_db
+                .get_accounts_delta_hash(self.slot())
+        };
+
         let mut hash = self.hash.write().unwrap();
+        let curr_accounts_delta_hash = get_delta_hash();
         let new = self.hash_internal_state();
+        if let Some(curr_accounts_delta_hash) = curr_accounts_delta_hash {
+            let new_accounts_delta_hash = get_delta_hash().unwrap();
+            assert_eq!(
+                new_accounts_delta_hash, curr_accounts_delta_hash,
+                "rehashing is not allowed to change the account state",
+            );
+        }
         if new != *hash {
-            warn!("Updating bank hash to {}", new);
+            warn!("Updating bank hash to {new}");
             *hash = new;
         }
     }

runtime/src/bank/tests.rs

@@ -13252,3 +13252,48 @@ fn test_bank_epoch_stakes() {
         );
     }
 }
+
+#[test]
+fn test_rehash_good() {
+    let ten_sol = 10 * LAMPORTS_PER_SOL;
+    let (genesis_config, _mint) = create_genesis_config(ten_sol);
+    let bank = Bank::new_for_tests(&genesis_config);
+
+    let lamports = 123_456_789;
+    let account = AccountSharedData::new(lamports, 0, &Pubkey::default());
+    let pubkey = Pubkey::new_unique();
+    bank.store_account_and_update_capitalization(&pubkey, &account);
+
+    // freeze the bank to trigger hash calculation
+    bank.freeze();
+
+    // ensure the bank hash is the same before and after rehashing
+    let prev_bank_hash = bank.hash();
+    bank.rehash();
+    let post_bank_hash = bank.hash();
+    assert_eq!(post_bank_hash, prev_bank_hash);
+}
+
+#[test]
+#[should_panic(expected = "rehashing is not allowed to change the account state")]
+fn test_rehash_bad() {
+    let ten_sol = 10 * LAMPORTS_PER_SOL;
+    let (genesis_config, _mint) = create_genesis_config(ten_sol);
+    let bank = Bank::new_for_tests(&genesis_config);
+
+    let mut account = AccountSharedData::new(ten_sol, 0, &Pubkey::default());
+    let pubkey = Pubkey::new_unique();
+    bank.store_account_and_update_capitalization(&pubkey, &account);
+
+    // freeze the bank to trigger hash calculation
+    bank.freeze();
+
+    // change an account, which will cause rehashing to panic
+    account.checked_add_lamports(ten_sol).unwrap();
+    bank.rc
+        .accounts
+        .store_accounts_cached((bank.slot(), [(&pubkey, &account)].as_slice()));
+
+    // let the show begin
+    bank.rehash();
+}