[PATCH 4.18 046/135] sfp: fix oops with ethtool -m

[Greg Kroah-Hartman]

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

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

From: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>

[ Upstream commit 126d6848ef13958e1cb959e96c21d19bc498ade9 ]

If a network interface is created prior to the SFP socket being
available, ethtool can request module information.  This unfortunately
leads to an oops:

Unable to handle kernel NULL pointer dereference at virtual address 00000008
pgd = (ptrval)
[00000008] *pgd=7c400831, *pte=00000000, *ppte=00000000
Internal error: Oops: 17 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 1480 Comm: ethtool Not tainted 4.19.0-rc3 #138
Hardware name: Broadcom Northstar Plus SoC
PC is at sfp_get_module_info+0x8/0x10
LR is at dev_ethtool+0x218c/0x2afc

Fix this by not filling in the network device's SFP bus pointer until
SFP is fully bound, thereby avoiding the core calling into the SFP bus
code.

Fixes: ce0aa27ff3f6 ("sfp: add sfp-bus to bridge between network devices and sfp cages")
Reported-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
Tested-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/phy/sfp-bus.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/phy/sfp-bus.c
+++ b/drivers/net/phy/sfp-bus.c
@@ -349,6 +349,7 @@ static int sfp_register_bus(struct sfp_b
 	}
 	if (bus->started)
 		bus->socket_ops->start(bus->sfp);
+	bus->netdev->sfp_bus = bus;
 	bus->registered = true;
 	return 0;
 }
@@ -357,6 +358,7 @@ static void sfp_unregister_bus(struct sf
 {
 	const struct sfp_upstream_ops *ops = bus->upstream_ops;
 
+	bus->netdev->sfp_bus = NULL;
 	if (bus->registered) {
 		if (bus->started)
 			bus->socket_ops->stop(bus->sfp);
@@ -438,7 +440,6 @@ static void sfp_upstream_clear(struct sf
 {
 	bus->upstream_ops = NULL;
 	bus->upstream = NULL;
-	bus->netdev->sfp_bus = NULL;
 	bus->netdev = NULL;
 }
 
@@ -467,7 +468,6 @@ struct sfp_bus *sfp_register_upstream(st
 		bus->upstream_ops = ops;
 		bus->upstream = upstream;
 		bus->netdev = ndev;
-		ndev->sfp_bus = bus;
 
 		if (bus->sfp) {
 			ret = sfp_register_bus(bus);