From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: [Patch net 00/16] net_sched: fix races with RCU callbacks Date: Thu, 26 Oct 2017 18:24:27 -0700 Message-ID: <20171027012443.3306-1-xiyou.wangcong@gmail.com> Cc: Chris Mi , Cong Wang , Daniel Borkmann , Jiri Pirko , John Fastabend , Jamal Hadi Salim , "Paul E. McKenney" To: netdev@vger.kernel.org Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:46864 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751932AbdJ0BY6 (ORCPT ); Thu, 26 Oct 2017 21:24:58 -0400 Received: by mail-pf0-f193.google.com with SMTP id p87so3778772pfj.3 for ; Thu, 26 Oct 2017 18:24:57 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Recently, the RCU callbacks used in TC filters and TC actions keep drawing my attention, they introduce at least 4 race condition bugs: 1. A simple one fixed by Daniel: commit c78e1746d3ad7d548bdf3fe491898cc453911a49 Author: Daniel Borkmann Date: Wed May 20 17:13:33 2015 +0200 net: sched: fix call_rcu() race on classifier module unloads 2. A very nasty one fixed by me: commit 1697c4bb5245649a23f06a144cc38c06715e1b65 Author: Cong Wang Date: Mon Sep 11 16:33:32 2017 -0700 net_sched: carefully handle tcf_block_put() 3. Two more bugs found by Chris: https://patchwork.ozlabs.org/patch/826696/ https://patchwork.ozlabs.org/patch/826695/ Usually RCU callbacks are simple, however for TC filters and actions, they are complex because at least TC actions could be destroyed together with the TC filter in one callback. And RCU callbacks are invoked in BH context, without locking they are parallel too. All of these contribute to the cause of these nasty bugs. Alternatively, we could also: a) Introduce a spinlock to serialize these RCU callbacks. But as I said in commit 1697c4bb5245 ("net_sched: carefully handle tcf_block_put()"), it is very hard to do because of tcf_chain_dump(). Potentially we need to do a lot of work to make it possible (if not impossible). b) Just get rid of these RCU callbacks, because they are not necessary at all, callers of these call_rcu() are all on slow paths and holding RTNL lock, so blocking is allowed in their contexts. However, David and Eric dislike adding synchronize_rcu() here. As suggested by Paul, we could defer the work to a workqueue and gain the permission of holding RTNL again without any performance impact, however, in tcf_block_put() we could have a deadlock when flushing workqueue while hodling RTNL lock, the trick here is to defer the work itself in workqueue and make it queued after all other works so that we keep the same ordering to avoid any use-after-free. Please see the first patch for details. Patch 1 introduces the infrastructure, patch 2~12 move each tc filter to the new tc filter workqueue, patch 13 adds an assertion to catch potential bugs like this, patch 14 closes another rcu callback race, patch 15 and patch 16 add new test cases. Reported-by: Chris Mi Cc: Daniel Borkmann Cc: Jiri Pirko Cc: John Fastabend Cc: Jamal Hadi Salim Cc: "Paul E. McKenney" Signed-off-by: Cong Wang Chris Mi (2): selftests: Introduce a new script to generate tc batch file selftests: Introduce a new test case to tc testsuite Cong Wang (14): net_sched: introduce a workqueue for RCU callbacks of tc filter net_sched: use tcf_queue_work() in basic filter net_sched: use tcf_queue_work() in bpf filter net_sched: use tcf_queue_work() in cgroup filter net_sched: use tcf_queue_work() in flow filter net_sched: use tcf_queue_work() in flower filter net_sched: use tcf_queue_work() in fw filter net_sched: use tcf_queue_work() in matchall filter net_sched: use tcf_queue_work() in u32 filter net_sched: use tcf_queue_work() in route filter net_sched: use tcf_queue_work() in rsvp filter net_sched: use tcf_queue_work() in tcindex filter net_sched: add rtnl assertion to tcf_exts_destroy() net_sched: fix call_rcu() race on act_sample module removal include/net/pkt_cls.h | 3 + include/net/sch_generic.h | 2 + net/sched/act_sample.c | 1 + net/sched/cls_api.c | 69 ++++++++++++++++------ net/sched/cls_basic.c | 20 ++++++- net/sched/cls_bpf.c | 19 +++++- net/sched/cls_cgroup.c | 22 +++++-- net/sched/cls_flow.c | 19 +++++- net/sched/cls_flower.c | 19 +++++- net/sched/cls_fw.c | 19 +++++- net/sched/cls_matchall.c | 19 +++++- net/sched/cls_route.c | 19 +++++- net/sched/cls_rsvp.h | 19 +++++- net/sched/cls_tcindex.c | 38 ++++++++++-- net/sched/cls_u32.c | 29 ++++++++- .../tc-testing/tc-tests/filters/tests.json | 23 +++++++- tools/testing/selftests/tc-testing/tdc.py | 20 +++++-- tools/testing/selftests/tc-testing/tdc_batch.py | 62 +++++++++++++++++++ tools/testing/selftests/tc-testing/tdc_config.py | 2 + 19 files changed, 367 insertions(+), 57 deletions(-) create mode 100755 tools/testing/selftests/tc-testing/tdc_batch.py -- 2.13.0