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From:   Lv Yunlong <lyl2019@mail.ustc.edu.cn>
To:     jmaloy@redhat.com, ying.xue@windriver.com, davem@davemloft.net,
        kuba@kernel.org
Cc:     netdev@vger.kernel.org, tipc-discussion@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Subject: [PATCH] net:tipc: Fix a double free in tipc_sk_mcast_rcv
Date:   Sun, 28 Mar 2021 00:30:29 -0700
Message-Id: <20210328073029.4325-1-lyl2019@mail.ustc.edu.cn>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In the if(skb_peek(arrvq) == skb) branch, it calls __skb_dequeue(arrvq) to get
the skb by skb = skb_peek(arrvq). Then __skb_dequeue() unlinks the skb from arrvq
and returns the skb which equals to skb_peek(arrvq). After __skb_dequeue(arrvq)
finished, the skb is freed by kfree_skb(__skb_dequeue(arrvq)) in the first time.

Unfortunately, the same skb is freed in the second time by kfree_skb(skb) after
the branch completed.

My patch removes kfree_skb() in the if(skb_peek(arrvq) == skb) branch, because
this skb will be freed by kfree_skb(skb) finally.

Fixes: cb1b728096f54 ("tipc: eliminate race condition at multicast reception")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
---
 net/tipc/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index cebcc104dc70..022999e0202d 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1265,7 +1265,7 @@ void tipc_sk_mcast_rcv(struct net *net, struct sk_buff_head *arrvq,
 		spin_lock_bh(&inputq->lock);
 		if (skb_peek(arrvq) == skb) {
 			skb_queue_splice_tail_init(&tmpq, inputq);
-			kfree_skb(__skb_dequeue(arrvq));
+			__skb_dequeue(arrvq);
 		}
 		spin_unlock_bh(&inputq->lock);
 		__skb_queue_purge(&tmpq);
-- 
2.25.1