rbd: avoid use-after-free in do_rbd_add() when rbd_dev_create() fails

If getting an ID or setting up a work queue in rbd_dev_create() fails,
use-after-free on rbd_dev->rbd_client, rbd_dev->spec and rbd_dev->opts
is triggered in do_rbd_add().  The root cause is that the ownership of
these structures is transfered to rbd_dev prematurely and they all end
up getting freed when rbd_dev_create() calls rbd_dev_free() prior to
returning to do_rbd_add().

Found by Linux Verification Center (linuxtesting.org) with SVACE, an
incomplete patch submitted by Natalia Petrova <n.petrova@fintech.ru>.

Cc: stable@vger.kernel.org
Fixes: 1643dfa4 ("rbd: introduce a per-device ordered workqueue")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

drivers/block/rbd.c

@@ -5292,8 +5292,7 @@ static void rbd_dev_release(struct device *dev)
 		module_put(THIS_MODULE);
 }
 
-static struct rbd_device *__rbd_dev_create(struct rbd_client *rbdc,
-					   struct rbd_spec *spec)
+static struct rbd_device *__rbd_dev_create(struct rbd_spec *spec)
 {
 	struct rbd_device *rbd_dev;
 
@@ -5338,9 +5337,6 @@ static struct rbd_device *__rbd_dev_create(struct rbd_client *rbdc,
 	rbd_dev->dev.parent = &rbd_root_dev;
 	device_initialize(&rbd_dev->dev);
 
-	rbd_dev->rbd_client = rbdc;
-	rbd_dev->spec = spec;
-
 	return rbd_dev;
 }
 
@@ -5353,12 +5349,10 @@ static struct rbd_device *rbd_dev_create(struct rbd_client *rbdc,
 {
 	struct rbd_device *rbd_dev;
 
-	rbd_dev = __rbd_dev_create(rbdc, spec);
+	rbd_dev = __rbd_dev_create(spec);
 	if (!rbd_dev)
 		return NULL;
 
-	rbd_dev->opts = opts;
-
 	/* get an id and fill in device name */
 	rbd_dev->dev_id = ida_simple_get(&rbd_dev_id_ida, 0,
 					 minor_to_rbd_dev_id(1 << MINORBITS),
@@ -5375,6 +5369,10 @@ static struct rbd_device *rbd_dev_create(struct rbd_client *rbdc,
 	/* we have a ref from do_rbd_add() */
 	__module_get(THIS_MODULE);
 
+	rbd_dev->rbd_client = rbdc;
+	rbd_dev->spec = spec;
+	rbd_dev->opts = opts;
+
 	dout("%s rbd_dev %p dev_id %d\n", __func__, rbd_dev, rbd_dev->dev_id);
 	return rbd_dev;
 
@@ -6736,7 +6734,7 @@ static int rbd_dev_probe_parent(struct rbd_device *rbd_dev, int depth)
 		goto out_err;
 	}
 
-	parent = __rbd_dev_create(rbd_dev->rbd_client, rbd_dev->parent_spec);
+	parent = __rbd_dev_create(rbd_dev->parent_spec);
 	if (!parent) {
 		ret = -ENOMEM;
 		goto out_err;
@@ -6746,8 +6744,8 @@ static int rbd_dev_probe_parent(struct rbd_device *rbd_dev, int depth)
 	 * Images related by parent/child relationships always share
 	 * rbd_client and spec/parent_spec, so bump their refcounts.
 	 */
-	__rbd_get_client(rbd_dev->rbd_client);
-	rbd_spec_get(rbd_dev->parent_spec);
+	parent->rbd_client = __rbd_get_client(rbd_dev->rbd_client);
+	parent->spec = rbd_spec_get(rbd_dev->parent_spec);
 
 	__set_bit(RBD_DEV_FLAG_READONLY, &parent->flags);