netdev - [net 4/5] can: j1939: j1939_sk_init(): set SOCK_RCU_FREE to call sk

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Message-Id: <20210619220115.2830761-5-mkl@pengutronix.de>
Date:   Sun, 20 Jun 2021 00:01:14 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, Oleksij Rempel <o.rempel@...gutronix.de>,
        linux-stable <stable@...r.kernel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        syzbot+bdf710cfc41c186fdff3@...kaller.appspotmail.com,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [net 4/5] can: j1939: j1939_sk_init(): set SOCK_RCU_FREE to call sk_destruct() after RCU is done

From: Oleksij Rempel <o.rempel@...gutronix.de>

Set SOCK_RCU_FREE to let RCU to call sk_destruct() on completion.
Without this patch, we will run in to j1939_can_recv() after priv was
freed by j1939_sk_release()->j1939_sk_sock_destruct()

Fixes: 25fe97cb7620 ("can: j1939: move j1939_priv_put() into sk_destruct callback")
Link: https://lore.kernel.org/r/20210617130623.12705-1-o.rempel@pengutronix.de
Cc: linux-stable <stable@...r.kernel.org>
Reported-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Reported-by: syzbot+bdf710cfc41c186fdff3@...kaller.appspotmail.com
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 net/can/j1939/main.c   | 4 ++++
 net/can/j1939/socket.c | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
index da3a7a7bcff2..08c8606cfd9c 100644
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -193,6 +193,10 @@ static void j1939_can_rx_unregister(struct j1939_priv *priv)
 	can_rx_unregister(dev_net(ndev), ndev, J1939_CAN_ID, J1939_CAN_MASK,
 			  j1939_can_recv, priv);
 
+	/* The last reference of priv is dropped by the RCU deferred
+	 * j1939_sk_sock_destruct() of the last socket, so we can
+	 * safely drop this reference here.
+	 */
 	j1939_priv_put(priv);
 }
 
diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 56aa66147d5a..fce8bc8afeb7 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -398,6 +398,9 @@ static int j1939_sk_init(struct sock *sk)
 	atomic_set(&jsk->skb_pending, 0);
 	spin_lock_init(&jsk->sk_session_queue_lock);
 	INIT_LIST_HEAD(&jsk->sk_session_queue);
+
+	/* j1939_sk_sock_destruct() depends on SOCK_RCU_FREE flag */
+	sock_set_flag(sk, SOCK_RCU_FREE);
 	sk->sk_destruct = j1939_sk_sock_destruct;
 	sk->sk_protocol = CAN_J1939;
 
-- 
2.30.2