4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nikita Yushchenko <nikita.yo...@cogentembedded.com>


[ 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().

Fixes: 83c0afaec7b7 ("net: dsa: Add new binding implementation")
Signed-off-by: Nikita Yushchenko <nikita.yo...@cogentembedded.com>
Reviewed-by: Andrew Lunn <and...@lunn.ch>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/dsa/dsa2.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -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;
 }
 


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