netdev - [patch -next] ipip: potential race in ip_tunnel_init

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Message-ID: <20130823081537.GB31293@elgon.mountain>
Date:	Fri, 23 Aug 2013 11:15:37 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: [patch -next] ipip: potential race in ip_tunnel_init_net()

Eric Dumazet says that my previous fix for an ERR_PTR dereference
(ea857f28ab 'ipip: dereferencing an ERR_PTR in ip_tunnel_init_net()')
could be racy and suggests the following fix instead.

Reported-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 24549b4..830de3f 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -854,16 +854,14 @@ int ip_tunnel_init_net(struct net *net, int ip_tnl_net_id,
 
 	rtnl_lock();
 	itn->fb_tunnel_dev = __ip_tunnel_create(net, ops, &parms);
-	rtnl_unlock();
-
-	if (IS_ERR(itn->fb_tunnel_dev))
-		return PTR_ERR(itn->fb_tunnel_dev);
 	/* FB netdevice is special: we have one, and only one per netns.
 	 * Allowing to move it to another netns is clearly unsafe.
 	 */
-	itn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL;
+	if (!IS_ERR(itn->fb_tunnel_dev))
+		itn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL;
+	rtnl_unlock();
 
-	return 0;
+	return PTR_RET(itn->fb_tunnel_dev);
 }
 EXPORT_SYMBOL_GPL(ip_tunnel_init_net);
 
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