rbd: don't leak parent_spec in rbd_dev_probe_parent()

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.

Cc: stable@vger.kernel.org # 3.10+, needs backporting for < 4.2
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>

1 files changed, 16 insertions, 20 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index f5e49b639818..028db28cb8a0 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5134,41 +5134,37 @@ 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, NULL);
-        if (!parent)
+        parent = rbd_dev_create(rbd_dev->rbd_client, rbd_dev->parent_spec,
+                                NULL);
+        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;
 }