[net,2/2] sh_eth: Fix ethtool operation crash when net device is down

The driver connects and disconnects the PHY device whenever the
net device is brought up and down.  The ethtool get_settings,
set_settings and nway_reset operations will dereference a null
or dangling pointer if called while it is down.

I think it would be preferable to keep the PHY connected, but there
may be good reasons not to.

As an immediate fix for this bug:
- Set the phydev pointer to NULL after disconnecting the PHY
- Change those three operations to return -ENODEV while the PHY is
  not connected

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
---
 drivers/net/ethernet/renesas/sh_eth.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

2015-01-16 9:51 GMT-08:00 Ben Hutchings <ben.hutchings@codethink.co.uk>:
> The driver connects and disconnects the PHY device whenever the
> net device is brought up and down.  The ethtool get_settings,
> set_settings and nway_reset operations will dereference a null
> or dangling pointer if called while it is down.
>
> I think it would be preferable to keep the PHY connected, but there
> may be good reasons not to.

phy_disconnect() is the canonical way to stop the PHY library state
machine, and avoid deferred work to be done and call the driver's
adjust_link function. This also boils down to calling phy_detach()
which can put the PHY in a low-power mode when implemented.

>
> As an immediate fix for this bug:
> - Set the phydev pointer to NULL after disconnecting the PHY
> - Change those three operations to return -ENODEV while the PHY is
>   not connected
>
> Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
> ---
>  drivers/net/ethernet/renesas/sh_eth.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
> index 0c4d5b5..28e3822 100644
> --- a/drivers/net/ethernet/renesas/sh_eth.c
> +++ b/drivers/net/ethernet/renesas/sh_eth.c
> @@ -1827,6 +1827,9 @@ static int sh_eth_get_settings(struct net_device *ndev,
>         unsigned long flags;
>         int ret;
>
> +       if (!mdp->phydev)
> +               return -ENODEV;

Since the PHY is disconnected, would not checking for netif_running()
make sense here, unless there is a good reason to still allow
phy_ethtool_gset() to be called?

> +
>         spin_lock_irqsave(&mdp->lock, flags);
>         ret = phy_ethtool_gset(mdp->phydev, ecmd);
>         spin_unlock_irqrestore(&mdp->lock, flags);
> @@ -1841,6 +1844,9 @@ static int sh_eth_set_settings(struct net_device *ndev,
>         unsigned long flags;
>         int ret;
>
> +       if (!mdp->phydev)
> +               return -ENODEV;
> +
>         spin_lock_irqsave(&mdp->lock, flags);
>
>         /* disable tx and rx */
> @@ -1875,6 +1881,9 @@ static int sh_eth_nway_reset(struct net_device *ndev)
>         unsigned long flags;
>         int ret;
>
> +       if (!mdp->phydev)
> +               return -ENODEV;
> +
>         spin_lock_irqsave(&mdp->lock, flags);
>         ret = phy_start_aneg(mdp->phydev);
>         spin_unlock_irqrestore(&mdp->lock, flags);
> @@ -2184,6 +2193,7 @@ static int sh_eth_close(struct net_device *ndev)
>         if (mdp->phydev) {
>                 phy_stop(mdp->phydev);
>                 phy_disconnect(mdp->phydev);
> +               mdp->phydev = NULL;
>         }
>
>         free_irq(ndev->irq, ndev);
> --
> 1.7.10.4
>
>
>
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On Fri, 2015-01-16 at 10:45 -0800, Florian Fainelli wrote:
> 2015-01-16 9:51 GMT-08:00 Ben Hutchings <ben.hutchings@codethink.co.uk>:
[...]
> > --- a/drivers/net/ethernet/renesas/sh_eth.c
> > +++ b/drivers/net/ethernet/renesas/sh_eth.c
> > @@ -1827,6 +1827,9 @@ static int sh_eth_get_settings(struct net_device *ndev,
> >         unsigned long flags;
> >         int ret;
> >
> > +       if (!mdp->phydev)
> > +               return -ENODEV;
> 
> Since the PHY is disconnected, would not checking for netif_running()
> make sense here, unless there is a good reason to still allow
> phy_ethtool_gset() to be called?
[...]

I think those two conditions will be equivalent, won't they?  Writing
the condition like this will also work if the driver later supports
PHY-less configurations.

Ben.


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On 19/01/15 02:41, Ben Hutchings wrote:
> On Fri, 2015-01-16 at 10:45 -0800, Florian Fainelli wrote:
>> 2015-01-16 9:51 GMT-08:00 Ben Hutchings <ben.hutchings@codethink.co.uk>:
> [...]
>>> --- a/drivers/net/ethernet/renesas/sh_eth.c
>>> +++ b/drivers/net/ethernet/renesas/sh_eth.c
>>> @@ -1827,6 +1827,9 @@ static int sh_eth_get_settings(struct net_device *ndev,
>>>         unsigned long flags;
>>>         int ret;
>>>
>>> +       if (!mdp->phydev)
>>> +               return -ENODEV;
>>
>> Since the PHY is disconnected, would not checking for netif_running()
>> make sense here, unless there is a good reason to still allow
>> phy_ethtool_gset() to be called?
> [...]
> 
> I think those two conditions will be equivalent, won't they?

They are indeed.

>  Writing the condition like this will also work if the driver later supports
> PHY-less configurations.

You could also represent a PHY-less configuration by using the emulated
fixed-PHY, such that the driver is effectively "driving" a PHY device,
even though this is not a real one, up to you.