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From:   Sun Ke <sunke32@huawei.com>
To:     <sunke32@huawei.com>, <josef@toxicpanda.com>, <axboe@kernel.dk>,
        <mchristi@redhat.com>
CC:     <linux-block@vger.kernel.org>, <nbd@other.debian.org>,
        <linux-kernel@vger.kernel.org>
Subject: [v2] nbd: fix potential NULL pointer fault in nbd_genl_disconnect
Date:   Mon, 20 Jan 2020 20:45:49 +0800
Message-ID: <20200120124549.27648-1-sunke32@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Open /dev/nbdX first, the config_refs will be 1 and
the pointers in nbd_device are still null. Disconnect
/dev/nbdX, then reference a null recv_workq. The
protection by config_refs in nbd_genl_disconnect is useless.

To fix it, just add a check for a non null task_recv in
nbd_genl_disconnect.

Signed-off-by: Sun Ke <sunke32@huawei.com>
---
v1 -> v2:

add an omitted mutex_unlock.
---
 drivers/block/nbd.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b4607dd96185..668bc9cb92ed 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -2008,6 +2008,10 @@ static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
 		       index);
 		return -EINVAL;
 	}
+	if (!nbd->task_recv) {
+		mutex_unlock(&nbd_index_mutex);
+		return -EINVAL;
+	}
 	if (!refcount_inc_not_zero(&nbd->refs)) {
 		mutex_unlock(&nbd_index_mutex);
 		printk(KERN_ERR "nbd: device at index %d is going down\n",
-- 
2.17.2