netdev - [Patch net] net_sched: check error pointer in tcf_dump

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Message-Id: <20201002191334.14135-1-xiyou.wangcong@gmail.com>
Date:   Fri,  2 Oct 2020 12:13:34 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+b47bc4f247856fb4d9e1@...kaller.appspotmail.com,
        Vlad Buslov <vladbu@...lanox.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: [Patch net] net_sched: check error pointer in tcf_dump_walker()

Although we take RTNL on dump path, it is possible to
skip RTNL on insertion path. So the following race condition
is possible:

rtnl_lock()		// no rtnl lock
			mutex_lock(&idrinfo->lock);
			// insert ERR_PTR(-EBUSY)
			mutex_unlock(&idrinfo->lock);
tc_dump_action()
rtnl_unlock()

So we have to skip those temporary -EBUSY entries on dump path
too.

Reported-and-tested-by: syzbot+b47bc4f247856fb4d9e1@...kaller.appspotmail.com
Fixes: 0fedc63fadf0 ("net_sched: commit action insertions together")
Cc: Vlad Buslov <vladbu@...lanox.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>
Cc: Jiri Pirko <jiri@...nulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/act_api.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 5612b336e18e..798430e1a79f 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -235,6 +235,8 @@ static int tcf_dump_walker(struct tcf_idrinfo *idrinfo, struct sk_buff *skb,
 		index++;
 		if (index < s_i)
 			continue;
+		if (IS_ERR(p))
+			continue;
 
 		if (jiffy_since &&
 		    time_after(jiffy_since,
-- 
2.28.0