[PATCH 4.4 16/38] net:tipc: Fix a double free in tipc_sk_mcast_rcv - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Lv Yunlong <lyl2019@mail.ustc.edu.cn>,
	"David S. Miller" <davem@davemloft.net>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.4 16/38] net:tipc: Fix a double free in tipc_sk_mcast_rcv
Date: Thu, 15 Apr 2021 16:47:10 +0200	[thread overview]
Message-ID: <20210415144413.867962999@linuxfoundation.org> (raw)
In-Reply-To: <20210415144413.352638802@linuxfoundation.org>

From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>

[ Upstream commit 6bf24dc0cc0cc43b29ba344b66d78590e687e046 ]

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 65171f8e8c45..0e5bb03c6425 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -763,7 +763,7 @@ 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);
-- 
2.30.2



