[PATCH 4.1 39/86] rbd: dont leak parent_spec in rbd_dev_probe_parent()

Greg Kroah-Hartman
2015-11-06T19:32:43Z

From: Ilya Dryomov <idryomov@gmail.com>

commit 1f2c6651f69c14d0d3a9cfbda44ea101b02160ba upstream.

Currently we leak parent_spec and trigger a "parent reference
underflow" warning if rbd_dev_create() in rbd_dev_probe_parent() fails.
The problem is we take the !parent out_err branch and that only drops
refcounts; parent_spec that would've been freed had we called
rbd_dev_unparent() remains and triggers rbd_warn() in
rbd_dev_parent_put() - at that point we have parent_spec != NULL and
parent_ref == 0, so counter ends up being -1 after the decrement.

Redo rbd_dev_probe_parent() to fix this.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
[idryomov@gmail.com: backport to < 4.2: rbd_dev->opts]
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/rbd.c | 35 +++++++++++++++--------------------
1 file changed, 15 insertions(+), 20 deletions(-)

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5148,41 +5148,36 @@ out_err:
static int rbd_dev_probe_parent(struct rbd_device *rbd_dev)
{
struct rbd_device *parent = NULL;
- struct rbd_spec *parent_spec;
- struct rbd_client *rbdc;
int ret;

if (!rbd_dev->parent_spec)
return 0;
- /*
- * We need to pass a reference to the client and the parent
- * spec when creating the parent rbd_dev. Images related by
- * parent/child relationships always share both.
- */
- parent_spec = rbd_spec_get(rbd_dev->parent_spec);
- rbdc = __rbd_get_client(rbd_dev->rbd_client);

- ret = -ENOMEM;
- parent = rbd_dev_create(rbdc, parent_spec);
- if (!parent)
+ parent = rbd_dev_create(rbd_dev->rbd_client, rbd_dev->parent_spec);
+ if (!parent) {
+ ret = -ENOMEM;
goto out_err;
+ }
+
+ /*
+ * 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);

ret = rbd_dev_image_probe(parent, false);
if (ret < 0)
goto out_err;
+
rbd_dev->parent = parent;
atomic_set(&rbd_dev->parent_ref, 1);
-
return 0;
+
out_err:
- if (parent) {
- rbd_dev_unparent(rbd_dev);
+ rbd_dev_unparent(rbd_dev);
+ if (parent)
rbd_dev_destroy(parent);
- } else {
- rbd_put_client(rbdc);
- rbd_spec_put(parent_spec);
- }
-
return ret;
}