linux-kernel - [PATCH 5.5 030/170] net_sched: hold rtnl lock in tcindex_partial_destroy

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Message-Id: <20200331085427.277734183@linuxfoundation.org>
Date:   Tue, 31 Mar 2020 10:57:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        syzbot+653090db2562495901dc@...kaller.appspotmail.com
Subject: [PATCH 5.5 030/170] net_sched: hold rtnl lock in tcindex_partial_destroy_work()

From: Cong Wang <xiyou.wangcong@...il.com>

[ Upstream commit b1be2e8cd290f620777bfdb8aa00890cd2fa02b5 ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sched/cls_tcindex.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -261,8 +261,10 @@ static void tcindex_partial_destroy_work
 					      struct tcindex_data,
 					      rwork);
 
+	rtnl_lock();
 	kfree(p->perfect);
 	kfree(p);
+	rtnl_unlock();
 }
 
 static void tcindex_free_perfect_hash(struct tcindex_data *cp)