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From:   Zhang Changzhong <zhangchangzhong@huawei.com>
To:     <robin@protonic.nl>, <linux@rempel-privat.de>,
        <kernel@pengutronix.de>, <socketcan@hartkopp.net>,
        <mkl@pengutronix.de>, <davem@davemloft.net>, <kuba@kernel.org>
CC:     <linux-can@vger.kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH net] can: j1939: j1939_sk_bind(): return failure if netdev is down
Date:   Mon, 7 Sep 2020 14:31:48 +0800
Message-ID: <1599460308-18770-1-git-send-email-zhangchangzhong@huawei.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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When a netdev down event occurs after a successful call to
j1939_sk_bind(), j1939_netdev_notify() can handle it correctly.

But if the netdev already in down state before calling j1939_sk_bind(),
j1939_sk_release() will stay in wait_event_interruptible() blocked
forever. Because in this case, j1939_netdev_notify() won't be called and
j1939_tp_txtimer() won't call j1939_session_cancel() or other function
to clear session for ENETDOWN error, this lead to mismatch of
j1939_session_get/put() and jsk->skb_pending will never decrease to
zero.

To reproduce it use following commands:
1. ip link add dev vcan0 type vcan
2. j1939acd -r 100,80-120 1122334455667788 vcan0
3. presses ctrl-c and thread will be blocked forever

This patch adds check for ndev->flags in j1939_sk_bind() to avoid this
kind of situation and return with -ENETDOWN.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
---
 net/can/j1939/socket.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 1be4c89..f239665 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -475,6 +475,12 @@ static int j1939_sk_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 			goto out_release_sock;
 		}
 
+		if (!(ndev->flags & IFF_UP)) {
+			dev_put(ndev);
+			ret = -ENETDOWN;
+			goto out_release_sock;
+		}
+
 		priv = j1939_netdev_start(ndev);
 		dev_put(ndev);
 		if (IS_ERR(priv)) {
-- 
2.9.5