From d0760c918ab75c837548ca27f19a46d387f77004 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Fri, 6 Nov 2026 04:31:04 +0100
Subject: strangers messages small

---
 src/transport/mycelium/mod.rs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'src/transport/mycelium/mod.rs')

diff --git a/src/transport/mycelium/mod.rs b/src/transport/mycelium/mod.rs
index 7bae0a7..369d683 100644
--- a/src/transport/mycelium/mod.rs
+++ b/src/transport/mycelium/mod.rs
@@ -89,6 +89,8 @@ pub(crate) struct MyceliumTransport {
     messages_endpoint: Url,
     pubkey_basepath: Url,
     local_id: String,
+    /// Whose messages may be large (`transport::Admission`).
+    admission: std::sync::OnceLock<crate::transport::Admission>,
 }
 
 /// This transport's options, checked when the configuration is loaded
@@ -247,6 +249,7 @@ impl MyceliumTransport {
             messages_endpoint: rest_url.join("/api/v1/messages")?,
             pubkey_basepath: rest_url.join("/api/v1/pubkey/")?,
             local_id: admin.node_pubkey,
+            admission: std::sync::OnceLock::new(),
         };
         transport.discard_backlog().await;
         Ok(transport)
@@ -317,6 +320,10 @@ impl MyceliumTransport {
 
 #[async_trait]
 impl Transport for MyceliumTransport {
+    fn set_admission(&self, admission: crate::transport::Admission) {
+        let _ = self.admission.set(admission);
+    }
+
     fn local_id(&self) -> &str {
         &self.local_id
     }
@@ -413,6 +420,21 @@ impl Transport for MyceliumTransport {
         // PINGs and PONGs aren't handled after the message before them (`is_probe`).
         let handler: std::sync::Arc<HandlerFn> = std::sync::Arc::from(handler);
         while let Some(inbound_message) = rx.recv().await {
+            // Mycelium has taken it whole already; a stranger's large one isn't decoded.
+            let limit = crate::transport::Admission::limit(
+                self.admission.get(),
+                SCHEME,
+                &inbound_message.src_pk,
+                MAX_INBOUND_BYTES,
+            );
+            if base64_decoded_len(&inbound_message.payload) > limit {
+                tracing::debug!(
+                    from = %Addressed(SCHEME, &inbound_message.src_pk),
+                    limit,
+                    "Dropping a large message from a peer not admitted"
+                );
+                continue;
+            }
             match parse_message(&inbound_message) {
                 Ok((sender, parsed)) => {
                     // The message itself is logged above, in the paths layer.
-- 
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