linux-kernel - [PATCH 3.16 299/305] vxlan: Fix error path in __vxlan_dev

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Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Petr Machata" <petrm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 299/305] vxlan: Fix error path in __vxlan_dev_create()

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

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

From: Petr Machata <petrm@...lanox.com>

commit 6db9246871394b3a136cd52001a0763676563840 upstream.

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/vxlan.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2615,6 +2615,7 @@ static int vxlan_newlink(struct net *net
 	struct vxlan_dev *vxlan = netdev_priv(dev), *tmp;
 	struct vxlan_rdst *dst = &vxlan->default_dst;
 	struct vxlan_fdb *f = NULL;
+	bool unregister = false;
 	__u32 vni;
 	int err;
 	bool use_ipv6 = false;
@@ -2766,12 +2767,11 @@ static int vxlan_newlink(struct net *net
 	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)
@@ -2780,9 +2780,16 @@ static int vxlan_newlink(struct net *net
 	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);
+	if (unregister)
+		unregister_netdevice(dev);
 	return err;
 }