From 4d416343fae4a9e0b1654b12bd476017be63a7e9 Mon Sep 17 00:00:00 2001 From: rinpatch Date: Fri, 28 Feb 2020 17:35:01 +0300 Subject: [PATCH] rate limiter: Fix a race condition When multiple requests are processed by rate limiter plug at the same time and the bucket is not yet initialized, both would try to initialize the bucket resulting in an internal server error. --- .../plugs/rate_limiter/limiter_supervisor.ex | 10 ++++-- .../plugs/rate_limiter/rate_limiter.ex | 15 ++++++--- test/plugs/rate_limiter_test.exs | 31 +++++++++++++++++++ 3 files changed, 49 insertions(+), 7 deletions(-) diff --git a/lib/pleroma/plugs/rate_limiter/limiter_supervisor.ex b/lib/pleroma/plugs/rate_limiter/limiter_supervisor.ex index 187582ede..884268d96 100644 --- a/lib/pleroma/plugs/rate_limiter/limiter_supervisor.ex +++ b/lib/pleroma/plugs/rate_limiter/limiter_supervisor.ex @@ -7,8 +7,8 @@ defmodule Pleroma.Plugs.RateLimiter.LimiterSupervisor do DynamicSupervisor.start_link(__MODULE__, init_arg, name: __MODULE__) end - def add_limiter(limiter_name, expiration) do - {:ok, _pid} = + def add_or_return_limiter(limiter_name, expiration) do + result = DynamicSupervisor.start_child( __MODULE__, %{ @@ -28,6 +28,12 @@ defmodule Pleroma.Plugs.RateLimiter.LimiterSupervisor do ]} } ) + + case result do + {:ok, _pid} = result -> result + {:error, {:already_started, pid}} -> {:ok, pid} + _ -> result + end end @impl true diff --git a/lib/pleroma/plugs/rate_limiter/rate_limiter.ex b/lib/pleroma/plugs/rate_limiter/rate_limiter.ex index 9c362a392..b9cbe9716 100644 --- a/lib/pleroma/plugs/rate_limiter/rate_limiter.ex +++ b/lib/pleroma/plugs/rate_limiter/rate_limiter.ex @@ -171,7 +171,7 @@ defmodule Pleroma.Plugs.RateLimiter do {:error, value} {:error, :no_cache} -> - initialize_buckets(action_settings) + initialize_buckets!(action_settings) check_rate(action_settings) end end @@ -250,11 +250,16 @@ defmodule Pleroma.Plugs.RateLimiter do |> String.replace_leading(":", "") end - defp initialize_buckets(%{name: _name, limits: nil}), do: :ok + defp initialize_buckets!(%{name: _name, limits: nil}), do: :ok - defp initialize_buckets(%{name: name, limits: limits}) do - LimiterSupervisor.add_limiter(anon_bucket_name(name), get_scale(:anon, limits)) - LimiterSupervisor.add_limiter(user_bucket_name(name), get_scale(:user, limits)) + defp initialize_buckets!(%{name: name, limits: limits}) do + {:ok, _pid} = + LimiterSupervisor.add_or_return_limiter(anon_bucket_name(name), get_scale(:anon, limits)) + + {:ok, _pid} = + LimiterSupervisor.add_or_return_limiter(user_bucket_name(name), get_scale(:user, limits)) + + :ok end defp attach_identity(base, %{mode: :user, conn_info: conn_info}), diff --git a/test/plugs/rate_limiter_test.exs b/test/plugs/rate_limiter_test.exs index 104d67611..8cdc8d1a2 100644 --- a/test/plugs/rate_limiter_test.exs +++ b/test/plugs/rate_limiter_test.exs @@ -242,4 +242,35 @@ defmodule Pleroma.Plugs.RateLimiterTest do refute conn_2.halted end end + + test "doesn't crash due to a race condition when multiple requests are made at the same time and the bucket is not yet initialized" do + limiter_name = :test_race_condition + Pleroma.Config.put([:rate_limit, limiter_name], {1000, 5}) + Pleroma.Config.put([Pleroma.Web.Endpoint, :http, :ip], {8, 8, 8, 8}) + + opts = RateLimiter.init(name: limiter_name) + + conn = conn(:get, "/") + conn_2 = conn(:get, "/") + + %Task{pid: pid1} = + task1 = + Task.async(fn -> + receive do + :process2_up -> + RateLimiter.call(conn, opts) + end + end) + + task2 = + Task.async(fn -> + send(pid1, :process2_up) + RateLimiter.call(conn_2, opts) + end) + + Task.await(task1) + Task.await(task2) + + refute {:err, :not_found} == RateLimiter.inspect_bucket(conn, limiter_name, opts) + end end