stake-pool: Improve error when overdrawing on decrease (#2522)

Author: joncinque

stake-pool/program/src/processor.rs

@@ -1019,7 +1019,7 @@ impl Processor {
             return Err(StakePoolError::InvalidState.into());
         }
 
-        let (_meta, stake) = get_stake_state(validator_stake_account_info)?;
+        let (meta, stake) = get_stake_state(validator_stake_account_info)?;
         let vote_account_address = stake.delegation.voter_pubkey;
         check_validator_stake_address(
             program_id,
@@ -1069,6 +1069,20 @@ impl Processor {
             return Err(ProgramError::AccountNotRentExempt);
         }
 
+        let remaining_lamports = validator_stake_account_info
+            .lamports()
+            .checked_sub(lamports)
+            .ok_or(ProgramError::InsufficientFunds)?;
+        let required_lamports = minimum_stake_lamports(&meta);
+        if remaining_lamports < required_lamports {
+            msg!("Need at least {} lamports in the stake account after decrease, {} requested, {} is the current possible maximum",
+                required_lamports,
+                lamports,
+                validator_stake_account_info.lamports().checked_sub(required_lamports).ok_or(StakePoolError::CalculationFailure)?
+            );
+            return Err(ProgramError::InsufficientFunds);
+        }
+
         create_transient_stake_account(
             transient_stake_account_info.clone(),
             transient_stake_account_signer_seeds,

stake-pool/program/tests/decrease.rs

@@ -367,7 +367,7 @@ async fn fail_with_small_lamport_amount() {
 }
 
 #[tokio::test]
-async fn fail_overdraw_validator() {
+async fn fail_big_overdraw() {
     let (
         mut banks_client,
         payer,
@@ -392,8 +392,43 @@ async fn fail_overdraw_validator() {
         .unwrap()
         .unwrap();
 
-    match error {
-        TransactionError::InstructionError(_, InstructionError::InsufficientFunds) => {}
-        _ => panic!("Wrong error occurs while overdrawing stake account on decrease"),
-    }
+    assert_eq!(
+        error,
+        TransactionError::InstructionError(0, InstructionError::InsufficientFunds)
+    );
+}
+
+#[tokio::test]
+async fn fail_overdraw() {
+    let (
+        mut banks_client,
+        payer,
+        recent_blockhash,
+        stake_pool_accounts,
+        validator_stake,
+        deposit_info,
+        _decrease_lamports,
+    ) = setup().await;
+
+    let rent = banks_client.get_rent().await.unwrap();
+    let stake_rent = rent.minimum_balance(std::mem::size_of::<stake_program::StakeState>());
+
+    let error = stake_pool_accounts
+        .decrease_validator_stake(
+            &mut banks_client,
+            &payer,
+            &recent_blockhash,
+            &validator_stake.stake_account,
+            &validator_stake.transient_stake_account,
+            deposit_info.stake_lamports + stake_rent + 1,
+            validator_stake.transient_stake_seed,
+        )
+        .await
+        .unwrap()
+        .unwrap();
+
+    assert_eq!(
+        error,
+        TransactionError::InstructionError(0, InstructionError::InsufficientFunds)
+    );
 }