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From:   Xiyu Yang <xiyuyang19@fudan.edu.cn>
To:     Jon Maloy <jmaloy@redhat.com>, Ying Xue <ying.xue@windriver.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org,
        tipc-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org
Cc:     yuanxzhang@fudan.edu.cn, kjlu@umn.edu,
        Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>
Subject: [PATCH] tipc: Fix potential tipc_node refcnt leak in tipc_rcv
Date:   Wed, 15 Apr 2020 16:40:28 +0800
Message-Id: <1586940029-69994-1-git-send-email-xiyuyang19@fudan.edu.cn>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

tipc_rcv() invokes tipc_node_find() twice, which returns a reference of
the specified tipc_node object to "n" with increased refcnt.

When tipc_rcv() returns or a new object is assigned to "n", the original
local reference of "n" becomes invalid, so the refcount should be
decreased to keep refcount balanced.

The issue happens in some paths of tipc_rcv(), which forget to decrease
the refcnt increased by tipc_node_find() and will cause a refcnt leak.

Fix this issue by calling tipc_node_put() before the original object
pointed by "n" becomes invalid.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 net/tipc/node.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 0c88778c88b5..d50be9a3d479 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -2037,6 +2037,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 		n = tipc_node_find_by_id(net, ehdr->id);
 	}
 	tipc_crypto_rcv(net, (n) ? n->crypto_rx : NULL, &skb, b);
+	tipc_node_put(n);
 	if (!skb)
 		return;
 
@@ -2089,7 +2090,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 	/* Check/update node state before receiving */
 	if (unlikely(skb)) {
 		if (unlikely(skb_linearize(skb)))
-			goto discard;
+			goto out_node_put;
 		tipc_node_write_lock(n);
 		if (tipc_node_check_state(n, skb, bearer_id, &xmitq)) {
 			if (le->link) {
@@ -2118,6 +2119,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 	if (!skb_queue_empty(&xmitq))
 		tipc_bearer_xmit(net, bearer_id, &xmitq, &le->maddr, n);
 
+out_node_put:
 	tipc_node_put(n);
 discard:
 	kfree_skb(skb);
-- 
2.7.4