netdev - [Patch net] net_sched: hold rtnl lock in tcindex_partial_destroy

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Date:   Wed, 11 Mar 2020 22:42:27 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+653090db2562495901dc@...kaller.appspotmail.com,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: [Patch net] net_sched: hold rtnl lock in tcindex_partial_destroy_work()

syzbot reported a use-after-free in tcindex_dump(). This is due to
the lack of RTNL in the deferred rcu work. We queue this work with
RTNL in tcindex_change(), later, tcindex_dump() is called:

        fh = tp->ops->get(tp, t->tcm_handle);
	...
        err = tp->ops->change(..., &fh, ...);
        tfilter_notify(..., fh, ...);

but there is nothing to serialize the pending
tcindex_partial_destroy_work() with tcindex_dump().

Fix this by simply holding RTNL in tcindex_partial_destroy_work(),
so that it won't be called until RTNL is released after
tc_new_tfilter() is completed.

Reported-and-tested-by: syzbot+653090db2562495901dc@...kaller.appspotmail.com
Fixes: 3d210534cc93 ("net_sched: fix a race condition in tcindex_destroy()")
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/cls_tcindex.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 09b7dc5fe7e0..f2cb24b6f0cf 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -261,8 +261,10 @@ static void tcindex_partial_destroy_work(struct work_struct *work)
 					      struct tcindex_data,
 					      rwork);
 
+	rtnl_lock();
 	kfree(p->perfect);
 	kfree(p);
+	rtnl_unlock();
 }
 
 static void tcindex_free_perfect_hash(struct tcindex_data *cp)
-- 
2.21.1