netdev - [PATCH] net/x25: Fix x25_neigh refcnt leak when reveiving frame

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Message-Id: <1587618786-13481-1-git-send-email-xiyuyang19@fudan.edu.cn>
Date:   Thu, 23 Apr 2020 13:13:03 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Andrew Hendry <andrew.hendry@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Allison Randal <allison@...utok.net>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] net/x25: Fix x25_neigh refcnt leak when reveiving frame

x25_lapb_receive_frame() invokes x25_get_neigh(), which returns a
reference of the specified x25_neigh object to "nb" with increased
refcnt.

When x25_lapb_receive_frame() returns, local variable "nb" becomes
invalid, so the refcount should be decreased to keep refcount balanced.

The reference counting issue happens in one path of
x25_lapb_receive_frame(). When pskb_may_pull() returns false, the
function forgets to decrease the refcnt increased by x25_get_neigh(),
causing a refcnt leak.

Fix this issue by calling x25_neigh_put() when pskb_may_pull() returns
false.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 net/x25/x25_dev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/x25/x25_dev.c b/net/x25/x25_dev.c
index 00e782335cb0..25bf72ee6cad 100644
--- a/net/x25/x25_dev.c
+++ b/net/x25/x25_dev.c
@@ -115,8 +115,10 @@ int x25_lapb_receive_frame(struct sk_buff *skb, struct net_device *dev,
 		goto drop;
 	}
 
-	if (!pskb_may_pull(skb, 1))
+	if (!pskb_may_pull(skb, 1)) {
+		x25_neigh_put(nb);
 		return 0;
+	}
 
 	switch (skb->data[0]) {
 
-- 
2.7.4