linux-kernel - [PATCH 3.16 222/346] batman-adv: Add missing refcnt for last

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Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Simon Wunderlich" <sw@...onwunderlich.de>,
        "Marek Lindner" <mareklindner@...mailbox.ch>,
        "Sven Eckelmann" <sven@...fation.org>
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@...fation.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@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
[bwh: Backported to 3.16:
 - s/kref_get/atomic_inc/
 - s/_put/_free_ref/]
Signed-off-by: Ben Hutchings <ben@...adent.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;
 }