linux-kernel - [PATCH 4.9 66/80] device-dax: fix cdev leak

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Date:   Thu, 18 May 2017 12:48:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Johannes Thumshirn <jthumshirn@...e.de>
Subject: [PATCH 4.9 66/80] device-dax: fix cdev leak

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

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

From: Dan Williams <dan.j.williams@...el.com>

commit ed01e50acdd3e4a640cf9ebd28a7e810c3ceca97 upstream.

If device_add() fails, cleanup the cdev. Otherwise, we leak a kobj_map()
with a stale device number.

As Jason points out, there is a small possibility that userspace has
opened and mapped the device in the time between cdev_add() and the
device_add() failure. We need a new kill_dax_dev() helper to invalidate
any established mappings.

Fixes: ba09c01d2fa8 ("dax: convert to the cdev api")
Reported-by: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/dax/dax.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -553,13 +553,10 @@ static void dax_dev_release(struct devic
 	kfree(dax_dev);
 }
 
-static void unregister_dax_dev(void *dev)
+static void kill_dax_dev(struct dax_dev *dax_dev)
 {
-	struct dax_dev *dax_dev = to_dax_dev(dev);
 	struct cdev *cdev = &dax_dev->cdev;
 
-	dev_dbg(dev, "%s\n", __func__);
-
 	/*
 	 * Note, rcu is not protecting the liveness of dax_dev, rcu is
 	 * ensuring that any fault handlers that might have seen
@@ -571,6 +568,15 @@ static void unregister_dax_dev(void *dev
 	synchronize_srcu(&dax_srcu);
 	unmap_mapping_range(dax_dev->inode->i_mapping, 0, 0, 1);
 	cdev_del(cdev);
+}
+
+static void unregister_dax_dev(void *dev)
+{
+	struct dax_dev *dax_dev = to_dax_dev(dev);
+
+	dev_dbg(dev, "%s\n", __func__);
+
+	kill_dax_dev(dax_dev);
 	device_unregister(dev);
 }
 
@@ -647,6 +653,7 @@ struct dax_dev *devm_create_dax_dev(stru
 	dev_set_name(dev, "dax%d.%d", dax_region->id, dax_dev->id);
 	rc = device_add(dev);
 	if (rc) {
+		kill_dax_dev(dax_dev);
 		put_device(dev);
 		return ERR_PTR(rc);
 	}