[PATCH v2] lan78xx: Connect phy early

From: Alexander Graf
Date: Tue Apr 03 2018 - 18:19:43 EST

When using wicked with a lan78xx device attached to the system, we
end up with ethtool commands issued on the device before an ifup
got issued. That lead to the following crash:

Unable to handle kernel NULL pointer dereference at virtual address 0000039c
pgd = ffff800035b30000
[0000039c] *pgd=0000000000000000
Internal error: Oops: 96000004 [#1] SMP
Modules linked in: [...]
Supported: Yes
CPU: 3 PID: 638 Comm: wickedd Tainted: G E 4.12.14-0-default #1
Hardware name: raspberrypi rpi/rpi, BIOS 2018.03-rc2 02/21/2018
task: ffff800035e74180 task.stack: ffff800036718000
PC is at phy_ethtool_ksettings_get+0x20/0x98
LR is at lan78xx_get_link_ksettings+0x44/0x60 [lan78xx]
pc : [<ffff0000086f7f30>] lr : [<ffff000000dcca84>] pstate: 20000005
sp : ffff80003671bb20
x29: ffff80003671bb20 x28: ffff800035e74180
x27: ffff000008912000 x26: 000000000000001d
x25: 0000000000000124 x24: ffff000008f74d00
x23: 0000004000114809 x22: 0000000000000000
x21: ffff80003671bbd0 x20: 0000000000000000
x19: ffff80003671bbd0 x18: 000000000000040d
x17: 0000000000000001 x16: 0000000000000000
x15: 0000000000000000 x14: ffffffffffffffff
x13: 0000000000000000 x12: 0000000000000020
x11: 0101010101010101 x10: fefefefefefefeff
x9 : 7f7f7f7f7f7f7f7f x8 : fefefeff31677364
x7 : 0000000080808080 x6 : ffff80003671bc9c
x5 : ffff80003671b9f8 x4 : ffff80002c296190
x3 : 0000000000000000 x2 : 0000000000000000
x1 : ffff80003671bbd0 x0 : ffff80003671bc00
Process wickedd (pid: 638, stack limit = 0xffff800036718000)
Call trace:
Exception stack(0xffff80003671b9e0 to 0xffff80003671bb20)
b9e0: ffff80003671bc00 ffff80003671bbd0 0000000000000000 0000000000000000
ba00: ffff80002c296190 ffff80003671b9f8 ffff80003671bc9c 0000000080808080
ba20: fefefeff31677364 7f7f7f7f7f7f7f7f fefefefefefefeff 0101010101010101
ba40: 0000000000000020 0000000000000000 ffffffffffffffff 0000000000000000
ba60: 0000000000000000 0000000000000001 000000000000040d ffff80003671bbd0
ba80: 0000000000000000 ffff80003671bbd0 0000000000000000 0000004000114809
baa0: ffff000008f74d00 0000000000000124 000000000000001d ffff000008912000
bac0: ffff800035e74180 ffff80003671bb20 ffff000000dcca84 ffff80003671bb20
bae0: ffff0000086f7f30 0000000020000005 ffff80002c296000 ffff800035223900
bb00: 0000ffffffffffff 0000000000000000 ffff80003671bb20 ffff0000086f7f30
[<ffff0000086f7f30>] phy_ethtool_ksettings_get+0x20/0x98
[<ffff000000dcca84>] lan78xx_get_link_ksettings+0x44/0x60 [lan78xx]
[<ffff0000087cbc40>] ethtool_get_settings+0x68/0x210
[<ffff0000087cc0d4>] dev_ethtool+0x214/0x2180
[<ffff0000087e5008>] dev_ioctl+0x400/0x630
[<ffff00000879dd00>] sock_do_ioctl+0x70/0x88
[<ffff00000879f5f8>] sock_ioctl+0x208/0x368
[<ffff0000082cde10>] do_vfs_ioctl+0xb0/0x848
[<ffff0000082ce634>] SyS_ioctl+0x8c/0xa8
Exception stack(0xffff80003671bec0 to 0xffff80003671c000)
bec0: 0000000000000009 0000000000008946 0000fffff4e841d0 0000aa0032687465
bee0: 0000aaaafa2319d4 0000fffff4e841d4 0000000032687465 0000000032687465
bf00: 000000000000001d 7f7fff7f7f7f7f7f 72606b622e71ff4c 7f7f7f7f7f7f7f7f
bf20: 0101010101010101 0000000000000020 ffffffffffffffff 0000ffff7f510c68
bf40: 0000ffff7f6a9d18 0000ffff7f44ce30 000000000000040d 0000ffff7f6f98f0
bf60: 0000fffff4e842c0 0000000000000001 0000aaaafa2c2e00 0000ffff7f6ab000
bf80: 0000fffff4e842c0 0000ffff7f62a000 0000aaaafa2b9f20 0000aaaafa2c2e00
bfa0: 0000fffff4e84818 0000fffff4e841a0 0000ffff7f5ad0cc 0000fffff4e841a0
bfc0: 0000ffff7f44ce3c 0000000080000000 0000000000000009 000000000000001d
bfe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000

The culprit is quite simple: The driver tries to access the phy left and right,
but only actually has a working reference to it when the device is up.

The fix thus is quite simple too: Get a reference to the phy on probe already
and keep it even when the device is going down.

With this patch applied, I can successfully run wicked on my system and bring
the interface up and down as many times as I want, without getting NULL pointer
dereferences in between.

Signed-off-by: Alexander Graf <agraf@xxxxxxx>

---

v1 -> v2:

- move debug message (Andrew Lunn)
- check for phydev != NULL before phy_stop (Sayed Nisar)
- move phy_disconnect before unregister_netdev (Sayed Nisar)
- properly unroll failing probe phy_init (Sayed Nisar)
- change phy_init to phy_start in reset_resume (Sayed Nisar)
---
drivers/net/usb/lan78xx.c | 34 ++++++++++++++++++----------------
1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index 60a604cc7647..6986f53fe967 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -2082,10 +2082,6 @@ static int lan78xx_phy_init(struct lan78xx_net *dev)

dev->fc_autoneg = phydev->autoneg;

- phy_start(phydev);
-
- netif_dbg(dev, ifup, dev->net, "phy initialised successfully");
-
return 0;

error:
@@ -2512,9 +2508,9 @@ static int lan78xx_open(struct net_device *net)
if (ret < 0)
goto done;

- ret = lan78xx_phy_init(dev);
- if (ret < 0)
- goto done;
+ phy_start(net->phydev);
+
+ netif_dbg(dev, ifup, dev->net, "phy initialised successfully");

/* for Link Check */
if (dev->urb_intr) {
@@ -2575,13 +2571,8 @@ static int lan78xx_stop(struct net_device *net)
if (timer_pending(&dev->stat_monitor))
del_timer_sync(&dev->stat_monitor);

- phy_unregister_fixup_for_uid(PHY_KSZ9031RNX, 0xfffffff0);
- phy_unregister_fixup_for_uid(PHY_LAN8835, 0xfffffff0);
-
- phy_stop(net->phydev);
- phy_disconnect(net->phydev);
-
- net->phydev = NULL;
+ if (net->phydev)
+ phy_stop(net->phydev);

clear_bit(EVENT_DEV_OPEN, &dev->flags);
netif_stop_queue(net);
@@ -3477,8 +3468,13 @@ static void lan78xx_disconnect(struct usb_interface *intf)
return;

udev = interface_to_usbdev(intf);
-
net = dev->net;
+
+ phy_unregister_fixup_for_uid(PHY_KSZ9031RNX, 0xfffffff0);
+ phy_unregister_fixup_for_uid(PHY_LAN8835, 0xfffffff0);
+
+ phy_disconnect(net->phydev);
+
unregister_netdev(net);

cancel_delayed_work_sync(&dev->wq);
@@ -3634,8 +3630,14 @@ static int lan78xx_probe(struct usb_interface *intf,
pm_runtime_set_autosuspend_delay(&udev->dev,
DEFAULT_AUTOSUSPEND_DELAY);

+ ret = lan78xx_phy_init(dev);
+ if (ret < 0)
+ goto out4;
+
return 0;

+out4:
+ unregister_netdev(netdev);
out3:
lan78xx_unbind(dev, intf);
out2:
@@ -3983,7 +3985,7 @@ static int lan78xx_reset_resume(struct usb_interface *intf)

lan78xx_reset(dev);

- lan78xx_phy_init(dev);
+ phy_start(dev->net->phydev);

return lan78xx_resume(intf);
}
--
2.12.3