netdev - [Patch net-next] l2tp: avoid overriding sk->sk_user

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Message-Id: <20240822182544.378169-1-xiyou.wangcong@gmail.com>
Date: Thu, 22 Aug 2024 11:25:44 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: netdev@...r.kernel.org
Cc: Cong Wang <cong.wang@...edance.com>,
	syzbot+8dbe3133b840c470da0e@...kaller.appspotmail.com,
	James Chapman <jchapman@...alix.com>,
	Tom Parkin <tparkin@...alix.com>
Subject: [Patch net-next] l2tp: avoid overriding sk->sk_user_data

From: Cong Wang <cong.wang@...edance.com>

Although commit 4a4cd70369f1 ("l2tp: don't set sk_user_data in tunnel socket")
removed sk->sk_user_data usage, setup_udp_tunnel_sock() still touches
sk->sk_user_data, this conflicts with sockmap which also leverages
sk->sk_user_data to save psock.

Restore this sk->sk_user_data check to avoid such conflicts.

Fixes: 4a4cd70369f1 ("l2tp: don't set sk_user_data in tunnel socket")
Reported-by: syzbot+8dbe3133b840c470da0e@...kaller.appspotmail.com
Cc: James Chapman <jchapman@...alix.com>
Cc: Tom Parkin <tparkin@...alix.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/l2tp/l2tp_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index af87c781d6a6..df73c35363cb 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1620,6 +1620,9 @@ static int l2tp_validate_socket(const struct sock *sk, const struct net *net,
 	    (encap == L2TP_ENCAPTYPE_IP && sk->sk_protocol != IPPROTO_L2TP))
 		return -EPROTONOSUPPORT;
 
+	if (encap == L2TP_ENCAPTYPE_UDP && sk->sk_user_data)
+		return -EBUSY;
+
 	tunnel = l2tp_sk_to_tunnel(sk);
 	if (tunnel) {
 		l2tp_tunnel_put(tunnel);
-- 
2.34.1