[PATCH 5.4 029/155] net_sched: hold rtnl lock in tcindex_partial_destroy_work()

Greg Kroah-Hartman
2020-03-31T09:11:52Z

From: Cong Wang <xiyou.wangcong@gmail.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@syzkaller.appspotmail.com
Fixes: 3d210534cc93 ("net_sched: fix a race condition in tcindex_destroy()")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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)