netdev - [PATCH net v3 2/4] vxlan: Fix error path in __vxlan_dev

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Date:   Tue, 18 Dec 2018 13:16:00 +0000
From:   Petr Machata <petrm@...lanox.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        Ido Schimmel <idosch@...lanox.com>,
        "roopa@...ulusnetworks.com" <roopa@...ulusnetworks.com>
Subject: [PATCH net v3 2/4] vxlan: Fix error path in __vxlan_dev_create()

When a failure occurs in rtnl_configure_link(), the current code
calls unregister_netdevice() to roll back the earlier call to
register_netdevice(), and jumps to errout, which calls
vxlan_fdb_destroy().

However unregister_netdevice() calls transitively ndo_uninit, which is
vxlan_uninit(), and that already takes care of deleting the default FDB
entry by calling vxlan_fdb_delete_default(). Since the entry added
earlier in __vxlan_dev_create() is exactly the default entry, the
cleanup code in the errout block always leads to double free and thus a
panic.

Besides, since vxlan_fdb_delete_default() always destroys the FDB entry
with notification enabled, the deletion of the default entry is notified
even before the addition was notified.

Instead, move the unregister_netdevice() call after the manual destroy,
which solves both problems.

Fixes: 0241b836732f ("vxlan: fix default fdb entry netlink notify ordering during netdev create")
Signed-off-by: Petr Machata <petrm@...lanox.com>
---

Notes:
    v3:
    - Reuse the same errout block for both cleanup paths. Use a bool to
      decide whether the unregister_netdevice() call should be made.
    
    v2:
    - Delete the default entry before calling unregister_netdevice(). That
      takes care of former patch #3, hence tweak the commit message to
      mention that problem as well.

 drivers/net/vxlan.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index c9956c08edf5..82e78d6fd9ae 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -3259,6 +3259,7 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
 	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	struct vxlan_fdb *f = NULL;
+	bool unregister = false;
 	int err;
 
 	err = vxlan_dev_configure(net, dev, conf, false, extack);
@@ -3284,12 +3285,11 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
 	err = register_netdevice(dev);
 	if (err)
 		goto errout;
+	unregister = true;
 
 	err = rtnl_configure_link(dev, NULL);
-	if (err) {
-		unregister_netdevice(dev);
+	if (err)
 		goto errout;
-	}
 
 	/* notify default fdb entry */
 	if (f)
@@ -3297,9 +3297,16 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
 
 	list_add(&vxlan->next, &vn->vxlan_list);
 	return 0;
+
 errout:
+	/* unregister_netdevice() destroys the default FDB entry with deletion
+	 * notification. But the addition notification was not sent yet, so
+	 * destroy the entry by hand here.
+	 */
 	if (f)
 		vxlan_fdb_destroy(vxlan, f, false);
+	if (unregister)
+		unregister_netdevice(dev);
 	return err;
 }
 
-- 
2.4.11