netdev - [PATCH net-next] tuntap: fix possible deadlock when fail to register netdev

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Message-Id: <1512701655-18751-1-git-send-email-jasowang@redhat.com>
Date:   Fri,  8 Dec 2017 10:54:15 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     mst@...hat.com, Jason Wang <jasowang@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] tuntap: fix possible deadlock when fail to register netdev

Private destructor could be called when register_netdev() fail with
rtnl lock held. This will lead deadlock in tun_free_netdev() who tries
to hold rtnl_lock. Fixing this by switching to use spinlock to
synchronize.

Fixes: 96f84061620c ("tun: add eBPF based queue selection method")
Reported-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/tun.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 787cc35..f7ccd79 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2050,8 +2050,11 @@ static int __tun_set_steering_ebpf(struct tun_struct *tun,
 		new->prog = prog;
 	}
 
-	old = rtnl_dereference(tun->steering_prog);
+	spin_lock(&tun->lock);
+	old = rcu_dereference_protected(tun->steering_prog,
+					lock_is_held(&tun->lock));
 	rcu_assign_pointer(tun->steering_prog, new);
+	spin_unlock(&tun->lock);
 
 	if (old)
 		call_rcu(&old->rcu, tun_steering_prog_free);
@@ -2067,9 +2070,7 @@ static void tun_free_netdev(struct net_device *dev)
 	free_percpu(tun->pcpu_stats);
 	tun_flow_uninit(tun);
 	security_tun_dev_free_security(tun->security);
-	rtnl_lock();
 	__tun_set_steering_ebpf(tun, NULL);
-	rtnl_unlock();
 }
 
 static void tun_setup(struct net_device *dev)
-- 
2.7.4