Send the membership id when kicking a remote user and drop KICKs with mismatching membership ids

This fixes the desync happening when a PART+JOIN crosses a KICK targetting
the same user.

2 files changed, 14 insertions, 0 deletions

diff --git a/src/coremods/core_channel/cmd_kick.cpp b/src/coremods/core_channel/cmd_kick.cpp
index dfa9bf217..051cc2678 100644
--- a/src/coremods/core_channel/cmd_kick.cpp
+++ b/src/coremods/core_channel/cmd_kick.cpp
@@ -73,6 +73,17 @@ CmdResult CommandKick::Handle (const std::vector<std::string>& parameters, User
 	}
 	Membership* const memb = victimiter->second;
 
+	// KICKs coming from servers can carry a membership id
+	if ((!IS_LOCAL(user)) && (parameters.size() > 3))
+	{
+		// If the current membership id is not equal to the one in the message then the user rejoined
+		if (memb->id != Membership::IdFromString(parameters[2]))
+		{
+			ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Dropped KICK due to membership id mismatch: " + ConvToStr(memb->id) + " != " + parameters[2]);
+			return CMD_FAILURE;
+		}
+	}
+
 	const bool has_reason = (parameters.size() > 2);
 	const std::string reason((has_reason ? parameters.back() : user->nick), 0, ServerInstance->Config->Limits.MaxKick);
 
diff --git a/src/modules/m_spanningtree/main.cpp b/src/modules/m_spanningtree/main.cpp
index 8154016e7..45f219286 100644
--- a/src/modules/m_spanningtree/main.cpp
+++ b/src/modules/m_spanningtree/main.cpp
@@ -624,6 +624,9 @@ void ModuleSpanningTree::OnUserKick(User* source, Membership* memb, const std::s
 	CmdBuilder params(source, "KICK");
 	params.push_back(memb->chan->name);
 	params.push_back(memb->user->uuid);
+	// If a remote user is being kicked by us then send the membership id in the kick too
+	if (!IS_LOCAL(memb->user))
+		params.push_int(memb->id);
 	params.push_last(reason);
 	params.Broadcast();
 }