Re: [PATCH 4.19 06/21] i40e: fix use-after-free in i40e_sync_filters_subtask()

Hi!

commit 3116f59c12bd24c513194cd3acb3ec1f7d468954 upstream.

Using ifconfig command to delete the ipv6 address will cause the i40e network card driver to delete its internal mac_filter and i40e_service_task kernel thread will concurrently access the mac_filter. These two processes are not protected by lock so causing the following use-after-free problems.

Ok, but...

+static void netdev_hw_addr_refcnt(struct i40e_mac_filter *f,

• 		  struct net_device *netdev, int delta)
  

+{

• struct netdev_hw_addr *ha;
• if (!f || !netdev)

• return;
  

• netdev_for_each_mc_addr(ha, netdev) {

• if (ether_addr_equal(ha->addr, f->macaddr)) {
  

• 	ha->refcount += delta;
  

• 	if (ha->refcount <= 0)
  

• 		ha->refcount = 1;
  

• 	break;
  

• }
  

• }

+}

What is going on here? Is refcount expected to underflow under normal operation? Should we at least have WARN_ON there?

Best regards, Pavel