reject MLS messages while in epoch 0

changelog.d/3-bug-fixes/mls-message-epoch-0

@@ -0,0 +1 @@
+Reject messages in MLS groups while in epoch 0.

integration/test/MLS/Util.hs

@@ -1015,16 +1015,17 @@ removeMemberFromChannel user channel userToBeRemoved = do
       }
 
 resetMLSConversation ::
-  (HasCallStack, MakesValue cid, MakesValue conv) =>
-  cid ->
+  (HasCallStack, MakesValue user, MakesValue conv) =>
+  user ->
+  ClientIdentity ->
   conv ->
   App Value
-resetMLSConversation cid conv = do
+resetMLSConversation user cid conv = do
   convId <- objConvId conv
   mlsConv <- getMLSConv convId
-  resetConversation cid mlsConv.groupId mlsConv.epoch >>= assertStatus 200
+  resetConversation user mlsConv.groupId mlsConv.epoch >>= assertStatus 200
 
-  conv' <- getConversation cid convId >>= getJSON 200
+  conv' <- getConversation user convId >>= getJSON 200
   groupId <- conv' %. "group_id" & asString
   groupId `shouldNotMatch` (mlsConv.groupId :: String)
   conv' %. "epoch" `shouldMatchInt` 0
@@ -1043,4 +1044,8 @@ resetMLSConversation cid conv = do
             )
             $ Map.delete convId mls.convs
       }
+
+  mlsConv' <- getMLSConv convId'
+  keys <- getMLSPublicKeys user >>= getJSON 200
+  resetClientGroup mlsConv'.ciphersuite cid mlsConv'.groupId convId' keys
   pure conv'

integration/test/Test/MLS.hs

@@ -92,6 +92,28 @@ testPastStaleApplicationMessage otherDomain = do
   -- bob's application messages are now rejected
   void $ postMLSMessage bob1 msg2.message >>= getJSON 409
 
+testEpochZeroApplicationMessage :: (HasCallStack) => App ()
+testEpochZeroApplicationMessage = do
+  [alice] <- createAndConnectUsers [make OwnDomain]
+  alice1 <- createMLSClient def alice
+  conv <- createNewGroup def alice1
+  void $ createAddCommit alice1 conv [] >>= sendAndConsumeCommitBundle
+  mlsConv <- getMLSConv conv
+
+  -- send message, make sure that's succeeding
+  msg <- createApplicationMessage mlsConv.convId alice1 "group is initialised"
+  postMLSMessage alice1 msg.message >>= assertStatus 201
+
+  -- reset conversation, so it exists on server and client with epoch 0
+  convId' <- objConvId =<< resetMLSConversation alice alice1 conv
+
+  -- send message, make sure that's failing
+  msg' <- createApplicationMessage convId' alice1 "group not initialised"
+  postMLSMessage alice1 msg'.message >>= flip withResponse \resp -> do
+    j <- getJSON 400 resp
+    j %. "label" `shouldMatch` "mls-protocol-error"
+    j %. "message" `shouldMatch` "Application messages at epoch 0 are not supported"
+
 testFutureStaleApplicationMessage :: (HasCallStack) => App ()
 testFutureStaleApplicationMessage = do
   [alice, bob, charlie] <- createAndConnectUsers [OwnDomain, OwnDomain, OwnDomain]

integration/test/Test/MLS/Reset.hs

@@ -62,7 +62,7 @@ testResetSelfConversation = do
   void $ createAddCommit alice1 convId [alice] >>= sendAndConsumeCommitBundle
   mlsConv <- getMLSConv convId
 
-  conv' <- resetMLSConversation alice conv
+  conv' <- resetMLSConversation alice alice1 conv
   conv' %. "group_id" `shouldNotMatch` (mlsConv.groupId :: String)
   conv' %. "epoch" `shouldMatchInt` 0
   convId' <- objConvId conv'
@@ -83,15 +83,15 @@ testResetOne2OneConversation = do
   otherDomain <- asString OtherDomain
   conv <- getMLSOne2OneConversation alice bob >>= getJSON 200
   convOwnerDomain <- asString $ conv %. "conversation.qualified_id.domain"
-  let user = if convOwnerDomain == otherDomain then bob else alice
+  let (user, cid) = if convOwnerDomain == otherDomain then (bob, bob1) else (alice, alice1)
   convId <- objConvId (conv %. "conversation")
 
   resetOne2OneGroup def alice1 conv
   void $ createAddCommit alice1 convId [bob] >>= sendAndConsumeCommitBundle
   void $ createPendingProposalCommit convId alice1 >>= sendAndConsumeCommitBundle
   mlsConv <- getMLSConv convId
 
-  conv' <- resetMLSConversation user (conv %. "conversation")
+  conv' <- resetMLSConversation user cid (conv %. "conversation")
   conv' %. "group_id" `shouldNotMatch` (mlsConv.groupId :: String)
   conv' %. "epoch" `shouldMatchInt` 0
   convId' <- objConvId conv'

services/galley/src/Galley/API/MLS/Message.hs

@@ -506,10 +506,13 @@ postMLSMessageToLocalConv qusr c con msg ctype convOrSubId = do
       for_ convOrSub.ciphersuite $ \ciphersuite -> do
         checkConversationOutOfSync mempty lConvOrSub ciphersuite
 
-      -- reject application messages older than 2 epochs
-      -- FUTUREWORK: consider rejecting this message if the conversation epoch is 0
+      -- reject application messages for epoch 0
       let epochInt :: Epoch -> Integer
           epochInt = fromIntegral . epochNumber
+      when (epochInt msg.epoch == 0) . throw $
+        mlsProtocolError "Application messages at epoch 0 are not supported"
+
+      -- reject application messages older than 2 epochs
       case convOrSub.mlsMeta.cnvmlsActiveData of
         Nothing -> throw $ mlsProtocolError "Application messages at epoch 0 are not supported"
         Just activeData ->