From 1b795c7b17a527edea1b52550e482dd8ee6b8c8d Mon Sep 17 00:00:00 2001
From: Travis Ralston <travpc@gmail.com>
Date: Wed, 4 Dec 2019 19:07:04 -0700
Subject: [PATCH] Add basic flooding protection too

---
 src/protections/BasicFlooding.ts | 72 ++++++++++++++++++++++++++++++++
 src/protections/protections.ts   |  6 +++
 2 files changed, 78 insertions(+)
 create mode 100644 src/protections/BasicFlooding.ts

diff --git a/src/protections/BasicFlooding.ts b/src/protections/BasicFlooding.ts
new file mode 100644
index 0000000..fc44ad5
--- /dev/null
+++ b/src/protections/BasicFlooding.ts
@@ -0,0 +1,72 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { IProtection } from "./IProtection";
+import { Mjolnir } from "../Mjolnir";
+import { LogLevel, LogService } from "matrix-bot-sdk";
+import { logMessage } from "../LogProxy";
+
+export const MAX_PER_MINUTE = 10; // if this is exceeded, we'll ban the user for spam and redact their messages
+const TIMESTAMP_THRESHOLD = 30000; // 30s out of phase
+
+export class BasicFlooding implements IProtection {
+
+    public lastEvents: { [roomId: string]: {[userId: string]: {originServerTs: number, eventId: string}[]} } = {};
+
+    constructor() {
+    }
+
+    public get name(): string {
+        return 'BasicFloodingProtection';
+    }
+
+    public async handleEvent(mjolnir: Mjolnir, roomId: string, event: any): Promise<any> {
+        if (!this.lastEvents[roomId]) this.lastEvents[roomId] = {};
+
+        const forRoom = this.lastEvents[roomId];
+        if (!forRoom[event['sender']]) forRoom[event['sender']] = [];
+        let forUser = forRoom[event['sender']];
+
+        if ((new Date()).getTime() - event['origin_server_ts'] > TIMESTAMP_THRESHOLD) {
+            LogService.warn("BasicFlooding", `${event['event_id']} is more than ${TIMESTAMP_THRESHOLD}ms out of phase - rewriting event time to be 'now'`);
+            event['origin_server_ts'] = (new Date()).getTime();
+        }
+
+        forUser.push({originServerTs: event['origin_server_ts'], eventId: event['event_id']});
+
+        // Do some math to see if the user is spamming
+        let messageCount = 0;
+        for (const prevEvent of forUser) {
+            if ((new Date()).getTime() - prevEvent.originServerTs > 60000) continue; // not important
+            messageCount++;
+        }
+
+        if (messageCount >= MAX_PER_MINUTE) {
+            await logMessage(LogLevel.WARN, "BasicFlooding", `Banning ${event['sender']} in ${roomId} for flooding (${messageCount} messages in the last minute)`);
+            await mjolnir.client.banUser(event['sender'], roomId, "spam");
+            // Redact all the things the user said too
+            for (const eventId of forUser.map(e => e.eventId)) {
+                await mjolnir.client.redactEvent(roomId, eventId, "spam");
+            }
+            forUser = forRoom[event['sender']] = []; // reset the user's list
+        }
+
+        // Trim the oldest messages off the user's history if it's getting large
+        if (forUser.length > MAX_PER_MINUTE*2) {
+            forUser.splice(0, forUser.length - (MAX_PER_MINUTE*2) - 1);
+        }
+    }
+}
diff --git a/src/protections/protections.ts b/src/protections/protections.ts
index 89e2a31..894a221 100644
--- a/src/protections/protections.ts
+++ b/src/protections/protections.ts
@@ -16,6 +16,7 @@ limitations under the License.
 
 import { FirstMessageIsImage } from "./FirstMessageIsImage";
 import { IProtection } from "./IProtection";
+import { BasicFlooding, MAX_PER_MINUTE } from "./BasicFlooding";
 
 export const PROTECTIONS: PossibleProtections = {
     [new FirstMessageIsImage().name]: {
@@ -23,6 +24,11 @@ export const PROTECTIONS: PossibleProtections = {
             "they'll be banned for spam. This does not publish the ban to any of your ban lists.",
         factory: () => new FirstMessageIsImage(),
     },
+    [new BasicFlooding().name]: {
+        description: "If a user posts more than " + MAX_PER_MINUTE + " messages in 60s they'll be " +
+            "banned for spam. This does not publish the ban to any of your ban lists.",
+        factory: () => new BasicFlooding(),
+    }
 };
 
 export interface PossibleProtections {