Reject blocks and transactions with the wrong number of authorizations

Author: 1440000bytes

lib/state/block.rs

@@ -84,6 +84,21 @@ pub fn validate(
         };
         return Err(err);
     }
+    // The authorization and address checks below pair authorizations with
+    // spent UTXOs positionally via `zip`, which silently ignores any trailing
+    // inputs when there are fewer authorizations than inputs requiring one.
+    // Require an exact count so that every input requiring authorization is
+    // covered by a provided authorization.
+    let n_authorizations_required: usize = filled_txs
+        .iter()
+        .map(|t| t.spent_utxos_requiring_auth().len())
+        .sum();
+    if body.authorizations.len() != n_authorizations_required {
+        return Err(Error::WrongNumberOfAuthorizations {
+            expected: n_authorizations_required,
+            received: body.authorizations.len(),
+        });
+    }
     let spent_utxos = filled_txs
         .iter()
         .flat_map(|t| t.spent_utxos_requiring_auth().into_iter());
@@ -168,6 +183,21 @@ pub fn prevalidate(
         };
         return Err(err);
     }
+    // The authorization and address checks below pair authorizations with
+    // spent UTXOs positionally via `zip`, which silently ignores any trailing
+    // inputs when there are fewer authorizations than inputs requiring one.
+    // Require an exact count so that every input requiring authorization is
+    // covered by a provided authorization.
+    let n_authorizations_required: usize = filled_transactions
+        .iter()
+        .map(|t| t.spent_utxos_requiring_auth().len())
+        .sum();
+    if body.authorizations.len() != n_authorizations_required {
+        return Err(Error::WrongNumberOfAuthorizations {
+            expected: n_authorizations_required,
+            received: body.authorizations.len(),
+        });
+    }
     let spent_utxos = filled_transactions
         .iter()
         .flat_map(|t| t.spent_utxos_requiring_auth().into_iter());

lib/state/error.rs

@@ -265,6 +265,10 @@ pub enum Error {
     UtxoDoubleSpent,
     #[error(transparent)]
     WithdrawalBundle(#[from] WithdrawalBundleError),
+    #[error(
+        "wrong number of authorizations: expected {expected}, but received {received}"
+    )]
+    WrongNumberOfAuthorizations { expected: usize, received: usize },
     #[error("wrong public key for address")]
     WrongPubKeyForAddress,
 }

lib/state/mod.rs

@@ -484,6 +484,17 @@ impl State {
     ) -> Result<bitcoin::Amount, Error> {
         let filled_transaction =
             self.fill_transaction(rotxn, &transaction.transaction)?;
+        // Pairing authorizations with spent UTXOs via `zip` silently ignores
+        // trailing inputs when there are too few authorizations. Require an
+        // exact count so that every input requiring authorization is covered.
+        let n_authorizations_required =
+            filled_transaction.spent_utxos_requiring_auth().len();
+        if transaction.authorizations.len() != n_authorizations_required {
+            return Err(Error::WrongNumberOfAuthorizations {
+                expected: n_authorizations_required,
+                received: transaction.authorizations.len(),
+            });
+        }
         for (authorization, spent_utxo) in transaction
             .authorizations
             .iter()