[3.16.y-ckt stable] Patch "rbd: don't leak parent_spec in rbd_dev_probe_parent()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    rbd: don't leak parent_spec in rbd_dev_probe_parent()

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt20.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 823a843a31fdbdca6133e6c49a72c5367f342e77 Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov at gmail.com>
Date: Sun, 11 Oct 2015 19:38:00 +0200
Subject: rbd: don't leak parent_spec in rbd_dev_probe_parent()

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 at gmail.com>
Reviewed-by: Alex Elder <elder at linaro.org>
[idryomov at gmail.com: backport to < 4.2: rbd_dev->opts]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/block/rbd.c | 35 +++++++++++++++--------------------
 1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 59584862a01b..5990cb7fb2fa 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5029,41 +5029,36 @@ 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;
 }