From 1a97d0a2f5f9b51478204346dbd2400e2ae71f51 Mon Sep 17 00:00:00 2001
From: Tanguy <tanguy@status.im>
Date: Fri, 14 Jan 2022 19:40:30 +0100
Subject: [PATCH] Validate pubsub subscriptions (#627)

* Check topic before subscribing
* Block subscribe to invalid topics
---
 libp2p/protocols/pubsub/pubsub.nim | 5 +++++
 tests/pubsub/testgossipsub2.nim    | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/libp2p/protocols/pubsub/pubsub.nim b/libp2p/protocols/pubsub/pubsub.nim
index 4c119ca97..30a30ed68 100644
--- a/libp2p/protocols/pubsub/pubsub.nim
+++ b/libp2p/protocols/pubsub/pubsub.nim
@@ -452,6 +452,11 @@ proc subscribe*(p: PubSub,
   ##               on every received message
   ##
 
+  # Check that this is an allowed topic
+  if p.subscriptionValidator != nil and p.subscriptionValidator(topic) == false:
+    warn "Trying to subscribe to a topic not passing validation!", topic
+    return
+
   p.topics.withValue(topic, handlers) do:
     # Already subscribed, just adding another handler
     handlers[].add(handler)
diff --git a/tests/pubsub/testgossipsub2.nim b/tests/pubsub/testgossipsub2.nim
index 62562c340..6e9c8913d 100644
--- a/tests/pubsub/testgossipsub2.nim
+++ b/tests/pubsub/testgossipsub2.nim
@@ -147,6 +147,9 @@ suite "GossipSub":
         nodes[1].start(),
     ))
 
+    # We must subscribe before setting the validator
+    nodes[0].subscribe("foobar", handler)
+
     var gossip = GossipSub(nodes[0])
     let invalidDetected = newFuture[void]()
     gossip.subscriptionValidator =
@@ -162,7 +165,6 @@ suite "GossipSub":
 
     await subscribeNodes(nodes)
 
-    nodes[0].subscribe("foobar", handler)
     nodes[1].subscribe("foobar", handler)
 
     await invalidDetected.wait(10.seconds)