netdev - [PATCH 5.4.y 1/1] net_sched: check error pointer in tcf_dump

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Message-Id: <1627574254-23665-2-git-send-email-george.kennedy@oracle.com>
Date:   Thu, 29 Jul 2021 10:57:34 -0500
From:   George Kennedy <george.kennedy@...cle.com>
To:     gregkh@...uxfoundation.org
Cc:     george.kennedy@...cle.com, xiyou.wangcong@...il.com,
        jhs@...atatu.com, jiri@...nulli.us, stable@...r.kernel.org,
        dhaval.giani@...cle.com, dan.carpenter@...cle.com,
        netdev@...r.kernel.org
Subject: [PATCH 5.4.y 1/1] net_sched: check error pointer in tcf_dump_walker()

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

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
(cherry picked from commit 580e4273d7a883ececfefa692c1f96bdbacb99b5)
Signed-off-by: George Kennedy <george.kennedy@...cle.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 17e5cd9..75132d0 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -231,6 +231,8 @@ 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,
-- 
1.8.3.1