Add ID checks to packet handling to reduce replay attack surface

usdpl-back/src/instance.rs

@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::sync::atomic::{AtomicU64, Ordering};
 
 use warp::Filter;
 
@@ -7,6 +8,9 @@ use usdpl_core::{socket, RemoteCallResponse};
 
 use super::{Callable, MutCallable, AsyncCallable, WrappedCallable};
 
+static LAST_ID: AtomicU64 = AtomicU64::new(0);
+const MAX_ID_DIFFERENCE: u64 = 5;
+
 //type WrappedCallable = Arc<Mutex<Box<dyn Callable>>>; // thread-safe, cloneable Callable
 
 #[cfg(feature = "encrypt")]
@@ -88,7 +92,22 @@ impl Instance {
     ) -> socket::Packet {
         match packet {
             socket::Packet::Call(call) => {
-                log::info!("Got USDPL call {} (`{}`, params: {})", call.id, call.function, call.parameters.len());
+                log::debug!("Got USDPL call {} (`{}`, params: {})", call.id, call.function, call.parameters.len());
+                let last_id = LAST_ID.load(Ordering::SeqCst);
+                if call.id == 0 {
+                    log::info!("Call ID is 0, assuming new connection (resetting last id)");
+                    LAST_ID.store(0, Ordering::SeqCst);
+                } else if call.id > last_id && call.id - last_id < MAX_ID_DIFFERENCE {
+                    LAST_ID.store(call.id, Ordering::SeqCst);
+                } else {
+                    #[cfg(not(debug_assertions))]
+                    {
+                        log::error!("Got USDPL call with strange ID! got:{} last id:{} (rejecting packet)", call.id, last_id);
+                        return socket::Packet::Invalid
+                    }
+                    #[cfg(debug_assertions)]
+                    log::warn!("Got USDPL call with strange ID! got:{} last id:{} (in release mode this packet will be rejected)", call.id, last_id);
+                }
                 //let handlers = CALLS.lock().expect("Failed to acquire CALLS lock");
                 if let Some(target) = handlers.get(&call.function) {
                     let result = target.call(call.parameters).await;