net: ethernet: fix potential use-after-free in ec_bhf_remove

stable inclusion
from stable-v4.19.196
commit 0260916843cc74f3906acf8b6f256693e01530a2
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9R4HZ
CVE: CVE-2021-47235

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0260916843cc74f3906acf8b6f256693e01530a2



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

[ Upstream commit 9cca0c2d ]

static void ec_bhf_remove(struct pci_dev *dev)
{
...
	struct ec_bhf_priv *priv = netdev_priv(net_dev);

	unregister_netdev(net_dev);
	free_netdev(net_dev);

	pci_iounmap(dev, priv->dma_io);
	pci_iounmap(dev, priv->io);
...
}

priv is netdev private data, but it is used
after free_netdev(). It can cause use-after-free when accessing priv
pointer. So, fix it by moving free_netdev() after pci_iounmap()
calls.

Fixes: 6af55ff5 ("Driver for Beckhoff CX5020 EtherCAT master module.")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kaixiong Yu <yukaixiong@huawei.com>