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From:   Xiyu Yang <xiyuyang19@fudan.edu.cn>
To:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Cong Wang <cong.wang@bytedance.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Tom Parkin <tparkin@katalix.com>,
        Xin Xiong <xiongx18@fudan.edu.cn>,
        "Gong, Sishuai" <sishuai@purdue.edu>,
        Matthias Schiffer <mschiffer@universe-factory.net>,
        Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Bhaskar Chowdhury <unixbhaskar@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     yuanxzhang@fudan.edu.cn, Xin Tan <tanxin.ctf@gmail.com>
Subject: [PATCH] net/l2tp: Fix reference count leak in l2tp_udp_recv_core
Date:   Thu,  9 Sep 2021 12:32:00 +0800
Message-Id: <1631161930-77772-1-git-send-email-xiyuyang19@fudan.edu.cn>
Precedence: bulk

The reference count leak issue may take place in an error handling
path. If both conditions of tunnel->version == L2TP_HDR_VER_3 and the
return value of l2tp_v3_ensure_opt_in_linear is nonzero, the function
would directly jump to label invalid, without decrementing the reference
count of the l2tp_session object session increased earlier by
l2tp_tunnel_get_session(). This may result in refcount leaks.

Fix this issue by decrease the reference count before jumping to the
label invalid.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Xiong <xiongx18@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 net/l2tp/l2tp_core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 53486b162f01..93271a2632b8 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -869,8 +869,10 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb)
 	}
 
 	if (tunnel->version == L2TP_HDR_VER_3 &&
-	    l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr))
+	    l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr)) {
+		l2tp_session_dec_refcount(session);
 		goto invalid;
+	}
 
 	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length);
 	l2tp_session_dec_refcount(session);
-- 
2.7.4