sdk: Check owner when verifying nonce accounts

sdk/src/nonce_account.rs

@@ -20,6 +20,9 @@ pub fn create_account(lamports: u64) -> RefCell<Account> {
 }
 
 pub fn verify_nonce_account(acc: &Account, hash: &Hash) -> bool {
+    if acc.owner != crate::system_program::id() {
+        return false;
+    }
     match StateMut::<Versions>::state(acc).map(|v| v.convert_to_current()) {
         Ok(State::Initialized(ref data)) => *hash == data.blockhash,
         _ => false,
@@ -35,3 +38,23 @@ pub fn fee_calculator_of(account: &Account) -> Option<FeeCalculator> {
         _ => None,
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::pubkey::Pubkey;
+
+    #[test]
+    fn test_verify_bad_account_owner_fails() {
+        let program_id = Pubkey::new_unique();
+        assert_ne!(program_id, crate::system_program::id());
+        let account = Account::new_data_with_space(
+            42,
+            &Versions::new_current(State::Uninitialized),
+            State::size(),
+            &program_id,
+        )
+        .expect("nonce_account");
+        assert!(!verify_nonce_account(&account, &Hash::default()));
+    }
+}