netdev - [PATCH] net: rtnetlink: Fix rtnl_dereference return value is NULL

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Date:   Thu,  8 Jul 2021 15:37:45 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     davem@...emloft.net, kuba@...nel.org, ryazanov.s.a@...il.com,
        johannes.berg@...el.com, avagin@...il.com, vladimir.oltean@....com,
        cong.wang@...edance.com, roopa@...ulusnetworks.com,
        yajun.deng@...ux.dev, zhudi21@...wei.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] net: rtnetlink: Fix rtnl_dereference return value is NULL

rtnl_dereference() may be return NULL in rtnl_unregister(),
so add this case handling.

Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 net/core/rtnetlink.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index f6af3e74fc44..57ce22669b06 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -289,24 +289,27 @@ int rtnl_unregister(int protocol, int msgtype)
 	struct rtnl_link __rcu **tab;
 	struct rtnl_link *link;
 	int msgindex;
+	int ret = -ENOENT;
 
 	BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
 	msgindex = rtm_msgindex(msgtype);
 
 	rtnl_lock();
 	tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
-	if (!tab) {
-		rtnl_unlock();
-		return -ENOENT;
-	}
+	if (!tab)
+		goto unlock;
 
 	link = rtnl_dereference(tab[msgindex]);
-	rcu_assign_pointer(tab[msgindex], NULL);
-	rtnl_unlock();
+	if (!link)
+		goto unlock;
 
+	rcu_assign_pointer(tab[msgindex], NULL);
 	kfree_rcu(link, rcu);
+	ret = 0;
 
-	return 0;
+unlock:
+	rtnl_unlock();
+	return ret;
 }
 EXPORT_SYMBOL_GPL(rtnl_unregister);
 
-- 
2.32.0