[B.A.T.M.A.N.] [PATCH maint] batman-adv: Add missing refcnt for last_candidate

[B.A.T.M.A.N.] [PATCH maint] batman-adv: Add missing refcnt for last_candidate

[Sven Eckelmann]

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: 797edd9e87ac ("batman-adv: add bonding again")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
This patch was only build tested.
---
 net/batman-adv/routing.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index bfac086..69d425d 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -456,6 +456,29 @@ static int batadv_check_unicast_packet(struct batadv_priv *bat_priv,
 }
 
 /**
+ * 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)
+		kref_get(&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
@@ -525,7 +548,7 @@ batadv_find_router(struct batadv_priv *bat_priv,
 	 * 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);
 
@@ -617,6 +640,9 @@ next:
 		batadv_orig_ifinfo_put(next_candidate);
 	}
 
+	if (last_candidate)
+		batadv_orig_ifinfo_put(last_candidate);
+
 	return router;
 }
 
-- 
2.8.1

Re: [B.A.T.M.A.N.] [PATCH maint] batman-adv: Add missing refcnt for last_candidate

[Marek Lindner]

[-- Attachment #1: Type: text/plain, Size: 805 bytes --]

On Saturday, August 6, 2016 3:50:52 PM HKT Sven Eckelmann wrote:
> 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: 797edd9e87ac ("batman-adv: add bonding again")
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> ---
> This patch was only build tested.
> ---
>  net/batman-adv/routing.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)

Applied in revision 008afae.

Thanks,
Marek


[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 455 bytes --]