linux-kernel - [PATCH 4.15 182/202] pktcdvd: Fix a recently introduced NULL pointer dereference

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Date:   Thu, 15 Feb 2018 16:18:02 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        Bart Van Assche <bart.vanassche@....com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.15 182/202] pktcdvd: Fix a recently introduced NULL pointer dereference

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

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

From: Bart Van Assche <bart.vanassche@....com>

commit 882d4171a8950646413b1a3cbe0e4a6a612fe82e upstream.

Call bdev_get_queue(bdev) after bdev->bd_disk has been initialized
instead of just before that pointer has been initialized. This patch
avoids that the following command

pktsetup 1 /dev/sr0

triggers the following kernel crash:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000548
IP: pkt_setup_dev+0x2db/0x670 [pktcdvd]
CPU: 2 PID: 724 Comm: pktsetup Not tainted 4.15.0-rc4-dbg+ #1
Call Trace:
 pkt_ctl_ioctl+0xce/0x1c0 [pktcdvd]
 do_vfs_ioctl+0x8e/0x670
 SyS_ioctl+0x3c/0x70
 entry_SYSCALL_64_fastpath+0x23/0x9a

Reported-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
Fixes: commit ca18d6f769d2 ("block: Make most scsi_req_init() calls implicit")
Signed-off-by: Bart Van Assche <bart.vanassche@....com>
Tested-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
Cc: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/pktcdvd.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -2579,14 +2579,14 @@ static int pkt_new_dev(struct pktcdvd_de
 	bdev = bdget(dev);
 	if (!bdev)
 		return -ENOMEM;
+	ret = blkdev_get(bdev, FMODE_READ | FMODE_NDELAY, NULL);
+	if (ret)
+		return ret;
 	if (!blk_queue_scsi_passthrough(bdev_get_queue(bdev))) {
 		WARN_ONCE(true, "Attempt to register a non-SCSI queue\n");
-		bdput(bdev);
+		blkdev_put(bdev, FMODE_READ | FMODE_NDELAY);
 		return -EINVAL;
 	}
-	ret = blkdev_get(bdev, FMODE_READ | FMODE_NDELAY, NULL);
-	if (ret)
-		return ret;

 	/* This is safe, since we have a reference from open(). */
 	__module_get(THIS_MODULE);