net:tipc: Fix a double free in tipc_sk_mcast_rcv

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>

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index cebcc104dc70ae6313278e2958e51a04909b956f..022999e0202d71d46b39b6d4785a4aca6a48731a 100644 (file)
--- 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);