Patch "net: dsa: fix unbalanced dsa_switch_tree reference counting" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

net: dsa: fix unbalanced dsa_switch_tree reference counting

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-dsa-fix-unbalanced-dsa_switch_tree-reference-counting.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nikita Yushchenko <[email protected]>
Date: Mon, 28 Nov 2016 09:48:48 +0300
Subject: net: dsa: fix unbalanced dsa_switch_tree reference counting

From: Nikita Yushchenko <[email protected]>

[ Upstream commit 7a99cd6e213685b78118382e6a8fed506c82ccb2 ]

_dsa_register_switch() gets a dsa_switch_tree object either via dsa_get_dst() or via dsa_add_dst(). Former path does not increase kref in returned object (resulting into caller not owning a reference), while later path does create a new object (resulting into caller owning a reference).

The rest of _dsa_register_switch() assumes that it owns a reference, and calls dsa_put_dst().

This causes a memory breakage if first switch in the tree initialized successfully, but second failed to initialize. In particular, freed dsa_swith_tree object is left referenced by switch that was initialized, and later access to sysfs attributes of that switch cause OOPS.

To fix, need to add kref_get() call to dsa_get_dst().

---
 net/dsa/dsa2.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -28,8 +28,10 @@ static struct dsa_switch_tree *dsa_get_d
 	struct dsa_switch_tree *dst;
 
 	list_for_each_entry(dst, &dsa_switch_trees, list)
-		if (dst->tree == tree)
+		if (dst->tree == tree) {
+			kref_get(&dst->refcount);
 			return dst;
+		}
 	return NULL;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/net-dsa-fix-unbalanced-dsa_switch_tree-reference-counting.patch