[PATCH v2 02/16] device-dax: fix cdev leak

Logan Gunthorpe
2017-02-26T06:38:03Z

From: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Cc: Logan Gunthorpe <logang-OTvnGxWRz7hWk0Htik3J/w@public.gmane.org>
Reported-by: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
Signed-off-by: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
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 ed758b7..b62a52f 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -630,13 +630,10 @@ 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
@@ -648,6 +645,15 @@ 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);
}

@@ -724,6 +730,7 @@ 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