linux-kernel - [PATCH 3.16 214/328] batman-adv: Use kref_get for batadv_nc_get_nc

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Message-ID: <lsq.1544392233.925561656@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Sven Eckelmann" <sven@...fation.org>,
        "Antonio Quartulli" <a@...table.cc>,
        "Marek Lindner" <mareklindner@...mailbox.ch>
Subject: [PATCH 3.16 214/328] batman-adv: Use kref_get for batadv_nc_get_nc_node

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Sven Eckelmann <sven@...fation.org>

commit 0de32ceee156787429035c974316f4e5098cf722 upstream.

batadv_nc_get_nc_node requires that the caller already has a valid
reference for orig_neigh_node. It is therefore not possible that it has an
reference counter of 0 and was still given to this function

The kref_get function instead WARNs (with debug information) when the
reference counter would still be 0. This makes a bug in batman-adv better
visible because kref_get_unless_zero would have ignored this problem.

Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Antonio Quartulli <a@...table.cc>
[bwh: Backported to 3.16: Reference counts are not krefs here, so open-
 code the equivalent of kref_get()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/batman-adv/network-coding.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

--- a/net/batman-adv/network-coding.c
+++ b/net/batman-adv/network-coding.c
@@ -813,8 +813,7 @@ static struct batadv_nc_node
 	if (!nc_node)
 		return NULL;
 
-	if (!atomic_inc_not_zero(&orig_neigh_node->refcount))
-		goto free;
+	WARN_ON_ONCE(atomic_inc_return(&orig_neigh_node->refcount) < 2);
 
 	/* Initialize nc_node */
 	INIT_LIST_HEAD(&nc_node->list);
@@ -840,10 +839,6 @@ static struct batadv_nc_node
 	spin_unlock_bh(lock);
 
 	return nc_node;
-
-free:
-	kfree(nc_node);
-	return NULL;
 }
 
 /**