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Subject[PATCH 3.16 222/346] batman-adv: Add missing refcnt for last_candidate
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Sven Eckelmann <sven@narfation.org>

commit 936523441bb64cdc9a5b263e8fd2782e70313a57 upstream.

batadv_find_router dereferences last_bonding_candidate from
orig_node without making sure that it has a valid reference. This reference
has to be retrieved by increasing the reference counter while holding
neigh_list_lock. The lock is required to avoid that
batadv_last_bonding_replace removes the current last_bonding_candidate,
reduces the reference counter and maybe destroys the object in this
process.

Fixes: f3b3d9018975 ("batman-adv: add bonding again")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16:
- s/kref_get/atomic_inc/
- s/_put/_free_ref/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/batman-adv/routing.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -425,6 +425,29 @@ static int batadv_check_unicast_packet(s
}

/**
+ * batadv_last_bonding_get - Get last_bonding_candidate of orig_node
+ * @orig_node: originator node whose last bonding candidate should be retrieved
+ *
+ * Return: last bonding candidate of router or NULL if not found
+ *
+ * The object is returned with refcounter increased by 1.
+ */
+static struct batadv_orig_ifinfo *
+batadv_last_bonding_get(struct batadv_orig_node *orig_node)
+{
+ struct batadv_orig_ifinfo *last_bonding_candidate;
+
+ spin_lock_bh(&orig_node->neigh_list_lock);
+ last_bonding_candidate = orig_node->last_bonding_candidate;
+
+ if (last_bonding_candidate)
+ atomic_inc(&last_bonding_candidate->refcount);
+ spin_unlock_bh(&orig_node->neigh_list_lock);
+
+ return last_bonding_candidate;
+}
+
+/**
* batadv_last_bonding_replace - Replace last_bonding_candidate of orig_node
* @orig_node: originator node whose bonding candidates should be replaced
* @new_candidate: new bonding candidate or NULL
@@ -492,7 +515,7 @@ batadv_find_router(struct batadv_priv *b
* router - obviously there are no other candidates.
*/
rcu_read_lock();
- last_candidate = orig_node->last_bonding_candidate;
+ last_candidate = batadv_last_bonding_get(orig_node);
if (last_candidate)
last_cand_router = rcu_dereference(last_candidate->router);

@@ -584,6 +607,9 @@ next:
batadv_orig_ifinfo_free_ref(next_candidate);
}

+ if (last_candidate)
+ batadv_orig_ifinfo_free_ref(last_candidate);
+
return router;
}

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