[PATCH 3.16 029/328] vxlan: fix default fdb entry netlink notify ordering during netdev create

Ben Hutchings
2018-12-09T22:28:38Z

From: Roopa Prabhu <roopa@cumulusnetworks.com>

commit 0241b836732f5f43c3f0fd9e9073c1fb24ea6757 upstream.

Problem:
In vxlan_newlink, a default fdb entry is added before register_netdev.
The default fdb creation function also notifies user-space of the
fdb entry on the vxlan device which user-space does not know about yet.
(RTM_NEWNEIGH goes before RTM_NEWLINK for the same ifindex).

This patch fixes the user-space netlink notification ordering issue
with the following changes:
- decouple fdb notify from fdb create.
- Move fdb notify after register_netdev.
- Call rtnl_configure_link in vxlan newlink handler to notify
userspace about the newlink before fdb notify and
hence avoiding the user-space race.

Fixes: afbd8bae9c79 ("vxlan: add implicit fdb entry for default destination")
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
- Drop changes to vxlan_changelink()
- Drop last argument to vxlan_fdb_destroy()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2614,6 +2614,7 @@ static int vxlan_newlink(struct net *net
struct vxlan_net *vn = net_generic(net, vxlan_net_id);
struct vxlan_dev *vxlan = netdev_priv(dev), *tmp;
struct vxlan_rdst *dst = &vxlan->default_dst;
+ struct vxlan_fdb *f = NULL;
__u32 vni;
int err;
bool use_ipv6 = false;
@@ -2751,27 +2752,38 @@ static int vxlan_newlink(struct net *net

/* create an fdb entry for a valid default destination */
if (!vxlan_addr_any(&vxlan->default_dst.remote_ip)) {
- err = vxlan_fdb_update(vxlan, all_zeros_mac,
+ err = vxlan_fdb_create(vxlan, all_zeros_mac,
&vxlan->default_dst.remote_ip,
NUD_REACHABLE|NUD_PERMANENT,
- NLM_F_EXCL|NLM_F_CREATE,
vxlan->dst_port,
vxlan->default_dst.remote_vni,
vxlan->default_dst.remote_ifindex,
- NTF_SELF);
+ NTF_SELF, &f);
if (err)
return err;
}

err = register_netdevice(dev);
+ if (err)
+ goto errout;
+
+ err = rtnl_configure_link(dev, NULL);
if (err) {
- vxlan_fdb_delete_default(vxlan);
- return err;
+ unregister_netdevice(dev);
+ goto errout;
}

+ /* notify default fdb entry */
+ if (f)
+ vxlan_fdb_notify(vxlan, f, first_remote_rtnl(f), RTM_NEWNEIGH);
+
list_add(&vxlan->next, &vn->vxlan_list);

return 0;
+errout:
+ if (f)
+ vxlan_fdb_destroy(vxlan, f);
+ return err;
}

static void vxlan_dellink(struct net_device *dev, struct list_head *head)