netdev - [PATCH net v2] net: bridge: Fix locking in br_fdb_find

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Message-Id: <c41fffa00abb9a123039e5509886a0de85274291.1528450455.git.petrm@mellanox.com>
Date:   Fri, 08 Jun 2018 15:11:47 +0200
From:   Petr Machata <petrm@...lanox.com>
To:     bridge@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     stephen@...workplumber.org, davem@...emloft.net,
        stephen@...workplumber.org
Subject: [PATCH net v2] net: bridge: Fix locking in br_fdb_find_port()

Callers of br_fdb_find() need to hold the hash lock, which
br_fdb_find_port() doesn't do. However, since br_fdb_find_port() is not
doing any actual FDB manipulation, the hash lock is not really needed at
all. So convert to br_fdb_find_rcu(), surrounded by rcu_read_lock() /
_unlock() pair.

The device pointer copied from inside the FDB entry is then kept alive
by the RTNL lock, which br_fdb_find_port() asserts.

Fixes: 4d4fd36126d6 ("net: bridge: Publish bridge accessor functions")
Signed-off-by: Petr Machata <petrm@...lanox.com>
---

Notes:
    Changes from v1 to v2:
    
    - Instead of taking hash lock, take RCU lock and call br_fdb_find_rcu().

 net/bridge/br_fdb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index b19e310..502f663 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -135,9 +135,11 @@ struct net_device *br_fdb_find_port(const struct net_device *br_dev,
 		return NULL;
 
 	br = netdev_priv(br_dev);
-	f = br_fdb_find(br, addr, vid);
+	rcu_read_lock();
+	f = br_fdb_find_rcu(br, addr, vid);
 	if (f && f->dst)
 		dev = f->dst->dev;
+	rcu_read_unlock();
 
 	return dev;
 }
-- 
2.4.11