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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Sven Eckelmann" <sven@narfation.org>,
        "Simon Wunderlich" <sw@simonwunderlich.de>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.880583766@decadent.org.uk>
Subject: [PATCH 3.16 220/328] batman-adv: Prevent duplicated tvlv handler
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
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3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Sven Eckelmann <sven@narfation.org>

commit ae3cdc97dc10c7a3b31f297dab429bfb774c9ccb upstream.

The function batadv_tvlv_handler_register is responsible for adding new
tvlv_handler to the handler_list. It first checks whether the entry
already is in the list or not. If it is, then the creation of a new entry
is aborted.

But the lock for the list is only held when the list is really modified.
This could lead to duplicated entries because another context could create
an entry with the same key between the check and the list manipulation.

The check and the manipulation of the list must therefore be in the same
locked code section.

Fixes: ef26157747d4 ("batman-adv: tvlv - basic infrastructure")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/batman-adv/main.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/batman-adv/main.c
+++ b/net/batman-adv/main.c
@@ -1058,15 +1058,20 @@ void batadv_tvlv_handler_register(struct
 {
 	struct batadv_tvlv_handler *tvlv_handler;
 
+	spin_lock_bh(&bat_priv->tvlv.handler_list_lock);
+
 	tvlv_handler = batadv_tvlv_handler_get(bat_priv, type, version);
 	if (tvlv_handler) {
+		spin_unlock_bh(&bat_priv->tvlv.handler_list_lock);
 		batadv_tvlv_handler_free_ref(tvlv_handler);
 		return;
 	}
 
 	tvlv_handler = kzalloc(sizeof(*tvlv_handler), GFP_ATOMIC);
-	if (!tvlv_handler)
+	if (!tvlv_handler) {
+		spin_unlock_bh(&bat_priv->tvlv.handler_list_lock);
 		return;
+	}
 
 	tvlv_handler->ogm_handler = optr;
 	tvlv_handler->unicast_handler = uptr;
@@ -1076,7 +1081,6 @@ void batadv_tvlv_handler_register(struct
 	atomic_set(&tvlv_handler->refcount, 1);
 	INIT_HLIST_NODE(&tvlv_handler->list);
 
-	spin_lock_bh(&bat_priv->tvlv.handler_list_lock);
 	hlist_add_head_rcu(&tvlv_handler->list, &bat_priv->tvlv.handler_list);
 	spin_unlock_bh(&bat_priv->tvlv.handler_list_lock);
 }