fix(confidential): reject set_spender with a past live_until_ledger

packages/confidential/src/lib.rs

@@ -596,6 +596,10 @@ pub enum ConfidentialTokenError {
     /// boundary to keep stored state and emitted events byte-unique per
     /// logical value.
     NonCanonicalEncoding = 3514,
+    /// Indicates `live_until_ledger` is already in the past
+    /// (`live_until_ledger < ledger.sequence()`), so the delegation would be
+    /// expired on arrival.
+    InvalidLiveUntilLedger = 3515,
 }
 
 // ################## CONSTANTS ##################

packages/confidential/src/storage.rs

@@ -846,6 +846,8 @@ pub fn confidential_transfer_from(
 ///
 /// # Errors
 ///
+/// * [`ConfidentialTokenError::InvalidLiveUntilLedger`] - When
+///   `live_until_ledger` is less than the current ledger number.
 /// * [`ConfidentialTokenError::AccountNotRegistered`] - When `account` or
 ///   `spender` is not registered.
 /// * [`ConfidentialTokenError::DelegationAlreadyExists`] - When a delegation
@@ -874,6 +876,13 @@ pub fn set_spender(
     payload: &SetSpenderPayload,
     proof: &Bytes,
 ) {
+    // Reject a delegation that would be expired on arrival before paying for
+    // the auditor lookup and proof verification. The bound is inclusive to
+    // match the liveness check (`ledger.sequence() <= live_until_ledger`).
+    if live_until_ledger < e.ledger().sequence() {
+        panic_with_error!(e, ConfidentialTokenError::InvalidLiveUntilLedger);
+    }
+
     let owner = get_account(e, account);
     let spender_account = get_account(e, spender);
     let auditor = ConfidentialAuditorClient::new(e, &get_auditor(e));

packages/confidential/src/test.rs

@@ -713,6 +713,36 @@ fn set_spender_twice_panics() {
     h.token.set_spender(&alice, &spender, &1_000u32, &set_spender_data(&h.e));
 }
 
+#[test]
+#[should_panic(expected = "Error(Contract, #3515)")]
+fn set_spender_with_past_live_until_ledger_panics() {
+    let h = setup();
+    let alice = Address::generate(&h.e);
+    let spender = Address::generate(&h.e);
+
+    h.token.register(&alice, &1u32, &register_data(&h.e));
+    h.token.register(&spender, &1u32, &register_data(&h.e));
+
+    h.e.ledger().set_sequence_number(100);
+    h.token.set_spender(&alice, &spender, &99u32, &set_spender_data(&h.e));
+}
+
+#[test]
+fn set_spender_with_current_ledger_is_live() {
+    let h = setup();
+    let alice = Address::generate(&h.e);
+    let spender = Address::generate(&h.e);
+
+    h.token.register(&alice, &1u32, &register_data(&h.e));
+    h.token.register(&spender, &1u32, &register_data(&h.e));
+
+    h.e.ledger().set_sequence_number(100);
+    h.token.set_spender(&alice, &spender, &100u32, &set_spender_data(&h.e));
+
+    assert_eq!(h.token.get_spender_delegation(&alice, &spender).live_until_ledger, 100);
+    assert!(h.token.is_spender(&alice, &spender));
+}
+
 #[test]
 fn revoke_spender_deletes_delegation() {
     let h = setup();