Token deposit: Require valid oracle for new token positions (#722)

This avoids making an account accidentally or intentionally unusable
(except for deposits/withdraws) by depositing a token with a stale
oracle.

programs/mango-v4/src/instructions/token_deposit.rs

@@ -179,7 +179,28 @@ pub fn token_deposit(ctx: Context<TokenDeposit>, amount: u64, reduce_only: bool)
     {
         let token_index = ctx.accounts.bank.load()?.token_index;
         let mut account = ctx.accounts.account.load_full_mut()?;
-        account.ensure_token_position(token_index)?;
+
+        let token_position_exists = account
+            .all_token_positions()
+            .any(|p| p.is_active_for_token(token_index));
+
+        // Activating a new token position requires that the oracle is in a good state.
+        // Otherwise users could abuse oracle staleness to delay liquidation.
+        if !token_position_exists {
+            let now_slot = Clock::get()?.slot;
+            let bank = ctx.accounts.bank.load()?;
+
+            let oracle_result = bank.oracle_price(
+                &AccountInfoRef::borrow(ctx.accounts.oracle.as_ref())?,
+                Some(now_slot),
+            );
+            if let Err(e) = oracle_result {
+                msg!("oracle must be valid when creating a new token position");
+                return Err(e);
+            }
+
+            account.ensure_token_position(token_index)?;
+        }
     }
 
     DepositCommon {

programs/mango-v4/tests/cases/test_stale_oracles.rs

@@ -67,7 +67,7 @@ async fn test_stale_oracle_deposit_withdraw() -> Result<(), TransportError> {
     .await
     .unwrap();
 
-    // Make both oracles invalid by increasing deviation
+    // Make oracles invalid by increasing deviation
     send_tx(
         solana,
         StubOracleSetTestInstruction {
@@ -94,6 +94,35 @@ async fn test_stale_oracle_deposit_withdraw() -> Result<(), TransportError> {
     )
     .await
     .unwrap();
+    send_tx(
+        solana,
+        StubOracleSetTestInstruction {
+            group,
+            mint: mints[2].pubkey,
+            admin,
+            price: 1.0,
+            last_update_slot: 0,
+            deviation: 100.0,
+        },
+    )
+    .await
+    .unwrap();
+
+    // Can't activate a token position for a bad oracle
+    assert!(send_tx(
+        solana,
+        TokenDepositInstruction {
+            amount: 11,
+            reduce_only: false,
+            account,
+            owner,
+            token_account: payer_token_accounts[2],
+            token_authority: payer.clone(),
+            bank_index: 0,
+        },
+    )
+    .await
+    .is_err());
 
     // Verify that creating a new borrow won't work
     assert!(send_tx(