[PATCH 4.9 22/31] vxlan: Fix GRO cells race condition between receive and link delete

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Stefano Brivio <sbrivio@redhat.com>

[ Upstream commit ad6c9986bcb627c7c22b8f9e9a934becc27df87c ]

If we receive a packet while deleting a VXLAN device, there's a chance
vxlan_rcv() is called at the same time as vxlan_dellink(). This is fine,
except that vxlan_dellink() should never ever touch stuff that's still in
use, such as the GRO cells list.

Otherwise, vxlan_rcv() crashes while queueing packets via
gro_cells_receive().

Move the gro_cells_destroy() to vxlan_uninit(), which runs after the RCU
grace period is elapsed and nothing needs the gro_cells anymore.

This is now done in the same way as commit 8e816df87997 ("geneve: Use GRO
cells infrastructure.") originally implemented for GENEVE.

Reported-by: Jianlin Shi <jishi@redhat.com>
Fixes: 58ce31cca1ff ("vxlan: GRO support at tunnel layer")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/vxlan.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2373,6 +2373,8 @@ static void vxlan_uninit(struct net_devi
 {
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 
+	gro_cells_destroy(&vxlan->gro_cells);
+
 	vxlan_fdb_delete_default(vxlan);
 
 	free_percpu(dev->tstats);
@@ -3123,7 +3125,6 @@ static void vxlan_dellink(struct net_dev
 {
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 
-	gro_cells_destroy(&vxlan->gro_cells);
 	list_del(&vxlan->next);
 	unregister_netdevice_queue(dev, head);
 }