linux-kernel - [PATCH 4.17 39/70] nbd: fix nbd device deletion

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Date:   Sun, 24 Jun 2018 23:22:31 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Josef Bacik <jbacik@...com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.17 39/70] nbd: fix nbd device deletion

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josef Bacik <jbacik@...com>

commit 8364da4751cf22201d74933d5e634176f44ed407 upstream.

This fixes a use after free bug, we shouldn't be doing disk->queue right
after we do del_gendisk(disk).  Save the queue and do the cleanup after
the del_gendisk.

Fixes: c6a4759ea0c9 ("nbd: add device refcounting")
cc: stable@...r.kernel.org
Signed-off-by: Josef Bacik <jbacik@...com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/nbd.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -173,9 +173,12 @@ static const struct device_attribute pid
 static void nbd_dev_remove(struct nbd_device *nbd)
 {
 	struct gendisk *disk = nbd->disk;
+	struct request_queue *q;
+
 	if (disk) {
+		q = disk->queue;
 		del_gendisk(disk);
-		blk_cleanup_queue(disk->queue);
+		blk_cleanup_queue(q);
 		blk_mq_free_tag_set(&nbd->tag_set);
 		disk->private_data = NULL;
 		put_disk(disk);