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@syzkaller.appspotmail.com
Fixes: c0ba7bbd3e74 ("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>

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 09b7dc5fe7e0a022e46947d18280901e37f40cf6..f2cb24b6f0cf54d9cc4ac2b81cc38f6f464fb6d9 100644 (file)
--- 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)