From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Tue, 18 Sep 2018 21:55:36 +0200
Subject: net: linkwatch: add check for netdevice being present to
 linkwatch_do_dev
Patch-mainline: v4.20-rc1
Git-commit: 124eee3f6955f7aa19b9e6ff5c9b6d37cb3d1e2c
References: bsc#1109837

When bringing down the netdevice (incl. detaching it) and calling
netif_carrier_off directly or indirectly the latter triggers an
asynchronous linkwatch event.
This linkwatch event eventually may fail to access chip registers in
the ndo_get_stats/ndo_get_stats64 callback because the device isn't
accessible any longer, see call trace in [0].

To prevent this scenario don't check for IFF_UP only, but also make
sure that the netdevice is present.

[0] https://lists.openwall.net/netdev/2018/03/15/62

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/link_watch.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -155,7 +155,7 @@ static void linkwatch_do_dev(struct net_
 	clear_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state);
 
 	rfc2863_policy(dev);
-	if (dev->flags & IFF_UP) {
+	if (dev->flags & IFF_UP && netif_device_present(dev)) {
 		if (netif_carrier_ok(dev))
 			dev_activate(dev);
 		else