linux-kernel - [PATCH 4.8 15/45] net: dsa: fix unbalanced dsa_switch

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Message-Id: <20161209161755.541943202@linuxfoundation.org>
Date:   Fri,  9 Dec 2016 17:20:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.8 15/45] net: dsa: fix unbalanced dsa_switch_tree reference counting

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

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

From: Nikita Yushchenko <nikita.yoush@...entembedded.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.yoush@...entembedded.com>
Reviewed-by: Andrew Lunn <andrew@...n.ch>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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;
 }