Reject transactions with extra signatures (#18306)

* Reject transactions with extra signatures

* fix tests

* fix check

* fix check

* tx method

* fix checks

sdk/src/feature_set.rs

@@ -147,6 +147,10 @@ pub mod dedupe_config_program_signers {
     solana_sdk::declare_id!("8kEuAshXLsgkUEdcFVLqrjCGGHVWFW99ZZpxvAzzMtBp");
 }
 
+pub mod verify_tx_signatures_len {
+    solana_sdk::declare_id!("EVW9B5xD9FFK7vw1SBARwMA4s5eRo5eKJdKpsBikzKBz");
+}
+
 lazy_static! {
     /// Map of feature identifiers to user-visible description
     pub static ref FEATURE_NAMES: HashMap<Pubkey, &'static str> = [

sdk/src/transaction.rs

@@ -361,6 +361,11 @@ impl Transaction {
         }
     }
 
+    /// Verify the length of signatures matches the value in the message header
+    pub fn verify_signatures_len(&self) -> bool {
+        self.signatures.len() == self.message.header.num_required_signatures as usize
+    }
+
     /// Verify the transaction and hash its message
     pub fn verify_and_hash_message(&self) -> Result<Hash> {
         let message_bytes = self.message_data();