linux-kernel - [PATCH v5 02/16] device-dax: fix cdev leak

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Date:   Fri, 17 Mar 2017 12:48:09 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:     linux-pci@...r.kernel.org, linux-scsi@...r.kernel.org,
        rtc-linux@...glegroups.com, linux-mtd@...ts.infradead.org,
        linux-media@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-input@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        <stable@...r.kernel.org>, Logan Gunthorpe <logang@...tatee.com>
Subject: [PATCH v5 02/16] device-dax: fix cdev leak

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

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")
Cc: <stable@...r.kernel.org>
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>
---
 drivers/dax/dax.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 8d9829f..a5ed59a 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -675,13 +675,10 @@ static void dax_dev_release(struct device *dev)
 	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
@@ -693,6 +690,15 @@ static void unregister_dax_dev(void *dev)
 	synchronize_rcu();
 	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);
 }
 
@@ -769,6 +775,7 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
 	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);
 	}
-- 
2.1.4